Dissertations / Theses on the topic 'Wet and Dry cycles'
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Olshansky, Yaniv, Robert A. Root, and Jon Chorover. "Wet–dry cycles impact DOM retention in subsurface soils." COPERNICUS GESELLSCHAFT MBH, 2018. http://hdl.handle.net/10150/627113.
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Transport and reactivity of carbon in the critical zone are highly controlled by reactions of dissolved organic matter (DOM) with subsurface soils, including adsorption, transformation and exchange. These reactions are dependent on frequent wet–dry cycles common to the unsaturated zone, particularly in semi-arid regions. To test for an effect of wet–dry cycles on DOM interaction and stabilization in subsoils, samples were collected from subsurface (Bw) horizons of an Entisol and an Alfisol from the Catalina-Jemez Critical Zone Observatory and sequentially reacted (four batch steps) with DOM extracted from the corresponding soil litter layers. Between each reaction step, soils either were allowed to air dry (wet–drytreatment) before introduction of the following DOM solution or were maintained under constant wetness (
continually wettreatment). Microbial degradation was the dominant mechanism of DOM loss from solution for the Entisol subsoil, which had higher initial organic C content, whereas sorptive retention predominated in the lower C Alfisol subsoil. For a given soil, bulk dissolved organic C losses from solution were similar across treatments. However, a combination of Fourier transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopic analyses revealed that wet–dry treatments enhanced the interactions between carboxyl functional groups and soil particle surfaces. Scanning transmission X-ray microscopy (STXM) data suggested that cation bridging by Ca2+ was the primary mechanism for carboxyl association with soil surfaces. STXM data also showed that spatial fractionation of adsorbed OM on soil organo-mineral surfaces was diminished relative to what might be inferred from previously published observations pertaining to DOM fractionation on reaction with specimen mineral phases. This study provides direct evidence of the role of wet–dry cycles in affecting sorption reactions of DOM to a complex soil matrix. In the soil environment, where wet–dry cycles occur at different frequencies from site to site and along the soil profile, different interactions between DOM and soil surfaces are expected and need to be considered for the overall assessment of carbon dynamics.
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Al-Hussaini, Osama. "Volume change behaviour of some geomaterials under combined influence of freeze-thaw and wet-dry cycles : an experimental investigation." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/110778/.
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Climate change has led to more extreme weather during the last decades. Seasonally hot weather regions have experienced harsh winters. Similarly, the global warming has contributed to raising the mean summer temperature in the cold regions. Geomaterials in various engineering applications are expected to experience such changes in the weather patterns and may undergo freezing, thawing, wetting and drying processes. This thesis presents an experimental study of the one-dimensional volume change behaviour of some geomaterials under the combined influence of freeze-thaw and wet-dry cycles. Laboratory tests were carried out on three selected materials (Speswhite kaolin, Pegwell Bay soil and cement kiln dust). A custom-made test set up was used to carry out the laboratory tests that enabled performing the required tests involving freezing, thawing, drying and wetting processes. Initially saturated slurried materials and compacted materials were subjected to freezing and thawing processes to study frost heave and thaw settlement. Compacted materials were taken through several wet-dry cycles and then exposed to freezing and thawing processes to study the impact of intermittent freeze-thaw cycles on the volume change behaviour of the materials. Similarly, compacted materials were subjected to an increasing number of freeze-thaw-wet-dry cycles to study the combined influence of various processes on the volume change behaviour of the materials. Compacted materials exhibited higher magnitudes of frost heave than initially saturated slurried materials. The swelling and shrinkage strains of compacted materials decreased with an increasing number of wet-dry cycles and attained an equilibrium at which the strains remained very similar. Intermittent freeze-thaw cycles were found to destabilize the equilibrium strain that was achieved during the previous wet-dry cycles; however, a new equilibrium in terms of the vertical strain was attained by the materials with an increasing number of wet-dry cycles. The materials having a history of being exposed to several wet-dry cycles exhibited a higher frost heave, a higher segregation potential and a greater magnitude of thaw settlement as compared to the same materials but without any cyclic wet-dry history. Upon subjected to an increasing number of wet-freeze-thaw-dry cycles, the materials exhibited uprising movement accompanied by strain accumulation prior to attaining an equilibrium at which the vertical strains associated with wetting, freezing, thawing and drying processes were found to be dissimilar; however, the sum of swelling deformation and frost heave was found to be equal to the sum of thaw settlement and shrinkage deformation.
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O'Keefe, Sorche. "The recovery of soils after compaction : a laboratory investigation into the effect of wet/dry cycles on bulk density and soil hydraulic functions." Thesis, Cranfield University, 2009. http://dspace.lib.cranfield.ac.uk/handle/1826/4493.
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Van den Akker et al. (2003) stated that “European subsoils are more threatened than ever in history” in an editorial referring to the results of the European Union concerted action “Experiences with the impact of subsoil compaction on soil crop growth and environment and ways to prevent subsoil compaction”. Compaction of agricultural soils not only reduces yields but can lead to pollution of surface waters and the release of greenhouse gases. Understanding, therefore, how, and to what extent, subsoil compaction may be reversed seems of vital importance. The literature suggests that soils with a range of textures could recover structural properties such as total and macro-porosity, infiltration rate and stability, although the extent and depth of these changes varies greatly. Factors affecting the extent and depth of changes are the rate of wetting and drying and the matric potentials achieved during drying (influenced by crop cover and irrigation practices as well as climate), organic matter content and tillage history. There is, however, a limited amount of information regarding changes to the pore-size distribution and unsaturated hydraulic conductivity of soils with wet/dry cycles. Although there are models able to predict the compaction that would occur for a given set of conditions, as well as the compactibility of soils and surface crack generation, there are no predictive models that describe structural changes due to wet/dry cycles. The aims of this study were to assess the changes in bulk density and hydrological parameters of a range of soils, of varying texture and other physical and chemical properties, with wet/dry cycles and to explore the relationships between any measured changes and the measured soil properties. A series of laboratory experiments were designed to measure changes to the total porosity and pore size distribution and hydraulic functions of soil samples. Changes to bulk density and moisture content of undisturbed soil cores at field capacity with wet/dry cycles were monitored. Changes to the moisture release curve and hydraulic conductivity curve (as well as bulk density) of remoulded clayey subsoil samples, with wet/dry cycles, were estimated using the multi-step outflow method. The surface cracking of the samples during the wetting and drying process was also explored. Changes to these parameters were statistically compared between soils and between initial bulk densities, and related to soil properties such as texture, organic matter content and Atterberg limits with a general linear model for repeated measures. Changes to the bulk density of the soils after three wet/dry cycles were found to be significantly different (at the 95 % probability level) between soils and between initial bulk densities. It was found that 90 % of the changes in bulk density could be predicted from the initial bulk density and the liquid limit of soils alone. The porosity gained or lost during wet/dry cycles was not confined to the macro-pore region, but included changes to pores that were undrained at pressures up to and including 100 m of water. Changes in the pore size distribution, as described by the parameters of the water release curve, modelled with the van Genuchten-Mualem equation, were found to be statistically related to soil texture and Atterberg limits. Changes to the hydraulic conductivity function of the soils were found to be affected by changes to the connectivity of the pore network, not just to changes in the volume of conducting pores. This was particularly true of the saturated hydraulic conductivity which was found to increase the most in soil samples that experienced a concomitant increase in bulk density and decrease in macro-porosity. Changes to the area of surface cracks were found to be significantly related to changes in the saturated hydraulic conductivity and to changes in the parameters of the van Genuchten-Mualem equation. It was also found that cracks did not close up entirely when the samples were saturated and there were many instances where wetting increased the area of surface cracks, relative to the preceding dry event, implying that the wetting phase was as important in structural formation as the drying phase. There is a strong suggestion that it would be possible to construct a relatively simple model, based on easily measurable parameters, which could be used to predict the changes to soil structure achievable with wet/dry cycles. Further research is needed, therefore, that extends the data set upon which the predictive model designed in this study was constructed. Refinement of the model to include information on the rates of wetting and drying would also contribute greatly to its applicability to the field situation. However, important steps have been made by this study towards a more comprehensive understanding of soil structural dynamics.
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Marchi, Fabio. "Effect of moisture susceptibility on different bituminous mastics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17619/.
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Moisture or water damage in asphalt mixtures can be defined as the loss of strength and durability, and an increase in stiffness leading to a more brittle behavior of materials and cause the adhesive failure at the binder-aggregate surface and/or cohesive failure within the binder or mastics. The performance and behaviour of asphalt mixtures are strictly dependent on the response of bituminous binders and mastics. The scope of this research is to acquire information on how moisture may affect rheological and chemical properties of different mastics made by different fillers. A neat bitumen and four mastics were prepared and tested, each of which combined with a specific filler. The conditioning procedure consisted in repeating wetting and drying cycles for three times. After each conditioning phase, couple of samples were tested by means of Dynamic Shear Rheometer (DSR) and Fourier Transfer Infrared spectrometer (FTIR). DSR was employed to determine the rheological properties of materials, such as the complex shear modulus (G*) and the phase angle (δ) at different temperatures and frequencies. FTIR has been used to investigate the chemical composition of bitumen and mastics after its reaction with water, in particular a specific range of wavelength was investigated to determine the absorption of the water and to combine data coming from rheological analysis. At high frequency and/or low temperature all materials behave as a solid; both rheological parameters (complex shear modulus and phase angle) tend to an asymptotic value throughout all the conditioning processes, whereas at low frequency and/or high temperatures is evident an increase of the complex shear modulus, due to water intrusion. Differences between mastics and neat bitumen are present in the intermediate frequency region. FTIR spectra for all mastics confirmed their rheological behavior.
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Foerster, Verena Elisabeth [Verfasser], Frank [Akademischer Betreuer] Schäbitz, and Olaf [Akademischer Betreuer] Bubenzer. "Late Quaternary climate variability in the source region of Homo sapiens. Dry-wet cycles in Chew Bahir, southern Ethiopia / Verena Elisabeth Foerster. Gutachter: Frank Schäbitz ; Olaf Bubenzer." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1071369873/34.
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Ji, Xiaoyan. "Thermodynamic properties of humid air and their application in advanced power generation cycles." Doctoral thesis, Stockholm : Department of Chemical and Engineering and Technology, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4129.
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BAJNI, GRETA. "STATISTICAL METHODS TO ASSESS ROCKFALL SUSCEPTIBILITY IN AN ALPINE ENVIRONMENT: A FOCUS ON CLIMATIC FORCING AND GEOMECHANICAL VARIABLES." Doctoral thesis, Università degli Studi di Milano, 2022. http://hdl.handle.net/2434/913511.
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The overarching goal of the doctoral thesis was thus the development of a systematic procedure capable to examine and enhance the role of geomechanical and climatic processes in rockfall susceptibility, performed with statistically based and Machine Learning techniques. To achieve this purpose, two case studies were analysed in the Italian Alps (Valchiavenna, Lombardy Region; Mountain Communities of Mont Cervin and Mont Emilius, Aosta Valley Region).
For both case studies, Generalized Additive Models (GAM) were used for rockfall susceptibility assessment; for the Valchiavenna case study, a Random Forest (RF) model was tested too. All models were validated through k-fold cross validation routines and their performance evaluated in terms of area under the receiver operating characteristic curve (AUROC). Predictors’ behaviour physical plausibility was verified through the analysis of the mathematical functions describing the predictors-susceptibility modelled relationships. Specific objectives of the two case studies differed.
The Valchiavenna case study was dedicated to testing the role of the outcrop-scale geomechanical properties in a rockfall susceptibility model. Specific objectives were: (i) the optimal selection of sampling points for the execution of geomechanical surveys to be integrated within an already available dataset; (ii) the regionalization over the study area of three geomechanical properties, namely Joint Volumetric Count (Jv), rock-mass weathering index (Wi) and rock-mass equivalent permeability (Keq); (iii) the implementation of the regionalized properties as predictors in a rockfall susceptibility model, along with the traditional morphometric variables; (iv) the investigation of prediction limitations related to inventory incompleteness; (v) the implementation of a methodology for the interpretation of predictors’ behaviour in the RF model, usually considered a black box algorithm; (vi) the integration of the RF and GAM outputs to furnish a spatially distributed measure of uncertainty; (vii) the exploitation of satellite-derived ground deformation data to verify susceptibility outputs and interpret them in an environmental management perspective.
The additional geomechanical sampling points were selected by means of the Spatial Simulated Annealing technique. Once collected the necessary geomechanical data, regionalization of the geomechanical target properties was carried out by comparing different deterministic, regressive and geostatistical techniques. The most suitable technique for each property was selected and geomechanical predictors were implemented in the susceptibility models. To verify rockfall inventory completeness related effects, the GAM model was performed both on rockfall data from the official landslide Italian inventory (IFFI) and on its updating with a field-mapped rockfall dataset. Regarding the RF model, the Shapely Additive exPlanations (SHAP) were employed for the interpretation of the predictors’ behaviour. A comparison between GAM and RF related outputs was carried out to verify their coherency, as well as a quantitative integration of the resulting susceptibility maps to reduce uncertainties. Finally, the rockfall susceptibility maps were coupled with Synthetic Aperture Radar (SAR) data from 2014 to 2021: a qualitative geomorphological verification of the outputs was performed, and composite maps were produced.
The key results were: (i) geomechanical predictor maps were obtained applying an ordinary kriging for Jv and Wi (NRMSE equal to 13.7% and 14.5%, respectively) and by means of Thin Plate Splines for Keq (NRMSE= 18.5%). (ii) Jv was the most important geomechanical predictor both in the GAM (witha deviance explained of 7.5%) and in the RF model, with a rockfall susceptibility increase in correspondence of the most fractured rock masses. (iii) Wi and Keq were penalized (i.e., they had low influence on rockfall susceptibility) in the GAM model, whereas Keq showed an importance comparable to Jv in the RF model. (iv) In a complex Machine Learning model (RF), the SHAPs allowed the interpretation of predictors’ behaviour, which demonstrated to be coherent with that shown in the GAM model. (v) The models including the geomechanical predictors resulted in acceptable rockfall discrimination capabilities (AUROC>0.7). (vi) The introduction of the geomechanical predictors led to a redistribution of the high-susceptibility areas in plausible geomorphological contexts, such as in correspondence of active slope deformations and structural lineaments, otherwise not revealed by the topographic predictors alone. (vii) Models built with solely the IFFI inventory, resulted in physically implausible susceptibility maps and predictor behaviour, highlighting a bias in the official inventory. (viii) The discordance in predicting rockfall susceptibility between the GAM and the RF models varied from 13% to 8% of the total study area. (ix) From the integration of InSAR data and susceptibility maps, a “SAR Integrated Susceptibility Map”, and an “Intervention Priority Map” were developed as operational products potentially exploitable in environmental planning activities.
The Aosta Valley case study was dedicated to challenge the concept of “susceptibility stationarity” by including the climate component in the rockfall susceptibility model. The availability of a large historical rockfall inventory and an extensive, multi-variable meteorological dataset for the period 1990-2020 were crucial input for the analysis. Specific objectives were: (i) the identification of climate conditions related to rockfall occurrence (ii) the summary of the identified relationships in variables to be used in a susceptibility model; (iii) the optimization of a rockfall susceptibility model, including both topographic, climatic and additional snow-related predictors (from a SWE weekly gridded dataset).
Starting from an hourly meteorological dataset, climate conditions were summarized in indices related to short-term rainfall (STR), effective water inputs (EWI, including rainfall and snow melting), wet-dry cycles (WD) and freeze-thaw cycles (FT). Climate indices and rockfall occurrence time series were paired. Critical thresholds relating rockfall occurrence to climate indices not-ordinary values (>75th percentile) were derived through a statistical analysis. As summary variables for the susceptibility analysis, the mean annual threshold exceedance frequency for each index was calculated. Model optimization consisted in stepwise modifications of the model settings in order to handle issues related to inventory bias, physical significance of climatic predictors and concurvity (i.e., predictors collinearity in GAMs). The starting point was a “blind model”, i.e., a susceptibility model created without awareness of the rockfall inventory characteristics and of the physical processes potentially influencing susceptibility. To reduce the inventory bias, “visibility” masks were produced so to limit the modelling domain according to the rockfall collection procedures adopted by administrations. Thirdly, models were optimized according to the physical plausibility of climatic predictors, analysed through the smooth functions relating them to susceptibility. Finally, to reduce concurvity, a Principal Component Analysis (PCA) including climatic and snow-related predictors was carried out. Subsequently, the obtained principal components were used to replace the climatic predictors in the susceptibility model.
The key results were: (i) the 95% of the rockfalls occurred in severe (or not ordinary) conditions for at least one among the EWI, WD and FT indices; (ii) ignoring inventory bias led to excellent model performance (0.80≤AUROC ≤0.90) but physically implausible outputs; (iii) the selection of non-rockfall points inside the “visibility mask” was a valuable approach to manage the inventory bias influence on outputs; (iv) the inclusion of climate predictors resulted in an improvement of the susceptibility model performance (AUROC up to 3%) in comparison to a topographic-based model; (v) the most important physically plausible climate predictors were EWI, WD, with a deviance explained varying from 5% to 10% each, followed by the maximum cumulated snow melting with a deviance explained varying from 3% to 5%. The effect of FT was masked by elevation. (vi) When the climate and snow related predictors were inserted in the susceptibility model as principal components, concurvity was efficiently reduced.
The inclusion of climate processes as non-stationary predictors (i.e., considering climate change) could be a valuable approach both to derive long-term rockfall susceptibility future scenarios and in combination with short-term weather forecasts to adapt susceptibility models to an early warning system for Civil Protection purpose.
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Thouin, Hugues. "Transfert de polluants inorganiques dans un technosol de brûlage d’armes organo-arséniées soumis à un apport de matière organique et à des cycles de saturation/désaturation : expérimentation en mésocosme." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2069/document.
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La destruction par brûlage de munitions chimiques de la Première Guerre Mondiale a provoqué une contamination importante de la partie supérieure du sol du site de la Place-à-Gaz par l’arsenic, le zinc, le cuivre et le plomb. Le traitement thermique a eu pour effet de minéraliser l’As des agents de guerre organoarséniés, et de former un assemblage minéral inattendu composé d’arséniates de Zn, Cu et Fe, et d’une phase amorphe riche en Fe, As, Zn, Cu et Pb. Ce matériel amorphe est la principale phase porteuse de l’As et des métaux dans la zone la plus polluée. Le site est sujet à des changements environnementaux pouvant affecter la stabilité des contaminants inorganiques. Afin d’évaluer l’impact d’épisodes de saturation en eau et de l’apport de matière organique sur les cycles biogéochimiques des métaux et de l’As, une étude en mésocosme a été menée. Les résultats montrent que la phase amorphe est instable en conditions saturées, et libère des contaminants dans l’eau interstitielle du sol. Comme sur le site, les contaminants les plus mobiles sont le Zn et l’As. L’addition de matière organique a induit une immobilisation de l’As, par piégeage de l’As V sur les oxyhydroxydes de fer, dans la partie saturée du sol. La caractérisation du compartiment microbien a été effectuée via des dénombrements, une analyse de la diversité bactérienne et des tests d’activités d’oxydation de l’As III et de respiration et. Les résultats montrent que les microorganismes ont contribué activement au métabolisme du C et de l’As. L’apport de matière organique a promu la croissance des microorganismes As III-oxydants et As Vréducteurs et modifié la structure des communautés bactériennes. Cependant, un effet négatif de la matière organique sur la vitesse d’oxydation de l’As III a été observé, entrainant une augmentation des concentrations d’As III en solution. Cette étude en mésocosme a montré que le dépôt naturel de litière organique a des conséquences antagonistes sur le transfert des contaminants inorganiques. Ces résultats fournissent de plus amples informations sur l’impact environnemental de la Grande Guerre et, de façon plus générale, sur les processus biogéochimiques contrôlant le comportement des métaux/métalloïdes sur les sites polluésThe thermal destruction of chemical munitions from World War I, on the site of “Place-à-Gaz”, induced intense local top soil contamination by arsenic and heavy metals. The heat treatment mineralized As from organoarsenic warfare agents, resulting in a singular mineral assemblage, composed of Zn, Cu and Fe arsenates and of an amorphous phase rich in Fe, As, Zn, Cu and Pb. The amorphous material was the principal carrier of As and metals in the central part of the site. The site undergoes environmental changes which may alter the stability of inorganic contaminants. To assess the impact of water saturation episodes and input of bioavailable organic matter on the biogeochemical cycles of metal(loid)s, a mesocosm study was conducted. Results showed that amorphous phase was instable in saturated conditions, and released contaminants in soil water. As previously observed on site, the most mobile contaminants were Zn and As. The addition of organic matter induced the immobilization of As by trapping of As V onto hydrous ferric oxides in the saturated soil. Microbial characterizations including counting, bacterial community structure, respiration, and determination of As IIIoxidizing activities were performed. Results showed that microorganisms actively contribute to the metabolisms of C and As.The addition of organic matter induced the increase of As III-oxidizing and As V-reducing microorganisms concentrations and modified the bacterial diversity. However, a negative effect of organic matter on the activity of As III oxidation was observed resulting in higher As III concentration in soil water. This study showed that the natural deposition of forest organic litter on the site, induced antagonist effects on the transfer of inorganic pollutants did not immobilize all the Zn and As and even contributed to As III transport to the surrounding environment. These results provide more information about the environmental impact of the Great War and more generally about the processes driving the behavior of metals/metalloids on polluted sites
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Cowan, Linda J. "The use of wet-to-dry dressings." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008780.
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Thesis (M.S.N.)--University of Florida, 2004.Typescript. Title from title page of source document. Document formatted into pages; contains 73 pages. Includes Vita. Includes bibliographical references.
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Susna, David. "Návrh chladícího okruhu pro odvod tepla z kondenzátoru parní turbíny." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378737.
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This thesis deals with the problems of wounding of low potential transferred from steam turbine condenser. First, in the theoretical part variations of steam condenser design are described. Then there is a description of variations of cooling cycles and possibilities of their operation range. In second part of the thesis there are two common cooler options chosen. Those are wet cooling tower with natural draft and dry chiller with forced draft. Two types of cooling liquid are chosen to be used for dry cooling. These are water and the other one is 50 % mixture of water and propylene glycol. Based on the calculation results of both cooling cycle variations appropriate pumps are chosen, fan for forced convection respectively. Parts of the thesis are also projection drawings for both calculated variations.
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Villa, Katherine. "The use of wet-to-dry dressings for mechanical debridement." Honors in the Major Thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/928.
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Clinical management of complex wounds is essential to promote wound healing. Prolonged healing time may lead to longer and more costly hospitalizations and poorer patient outcomes. The removal of nonviable, necrotic tissue via debridement is vital to the healing process. One of the most common debridement techniques, in the United States, is the use of wet-to-dry dressings. There are no defined guidelines or protocols for the timing of dressing changes and subsceequent debridement. The purpose of this study was to perform a review of literature to determine the rationale for the use of wet-to-dry dressings, explore alternative time sequences of treatment, and to identify the risks and benefits for this methodology of debridement in an adult population with acute traumas. Inclusion criteria consisted of peer reviewed, English Language, research articles published within the last 5 years (2007-2012), adults with acute wounds treated by wet-to-dry dressing debridement. This review of literature was conducted using CINAHL and MEDLINE databases using the following search terms: Wound debridement, wet-to-dry dressing', timing, sequencing, schedul', standard', debridement, acute wound', and mechanical debridement. The review of literature yielded zero results meeting the search criteria therefore, a second review of literature was performed using the same search criteria but expanded to include articles published within the past 15 years (1997 -2012). The second review of literature also yielded zero results that met the search criteria. A lack of evidence supporting the use of wet-to-dry dressings for the purpose of debridement suggests that healthcare providers are following tradition rather than evidence based practices. Nurses and healthcare providers need education on best practices in wound care to advocate for their patients to ensure the best possible outcome. Further research on wound care modalities that are clinically efficient is needed.B.S.N.
Bachelors
Nursing
Nursing
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Barclay, Jennifer Jayne. "Wet and dry troughs over Southern Africa during early summer." Master's thesis, University of Cape Town, 1992. http://hdl.handle.net/11427/21786.
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The synoptic scale structure of troughs transiting southern Africa in October and November is examined. Cases are chosen on the basis of an upper trough being present over southern Africa, and a minimum horizontal and vertical temperature change. Wet and dry troughs are differentiated by the extent and amount of interior rainfall produced. Once selected, a spatial and temporal framework was used on surface, upper-level synoptic maps and radiosonde sections. Individual and composite time-height and spatial sections are analysed for anomalies of temperature, geopotentials, kinematic, vorticity and divergence fields, dewpoint, dewpoint depression, mixing ratio, dry and total static energy and, equivalent potential temperature. European Centre for Medium Range Forecast (ECMWF) maps of vertical motion are analysed and ECMWF data were exclusively used in the wet and dry case study. The essential features of wet troughs include a large amplitude upper westerly wave with a diffluent and northward displaced sub-tropical jet stream, slow movement, westward tilted trough in the vertical and a negative - positive dipole where a high is located south of the low pressure system. In comparison dry troughs are characterised by a small amplitude upper wave, rapid movement, no tilted trough in the vertical, and a stationary high-pressure system over the western interior. Radiosonde moisture variables, circulation anomalies and ECMWF fields of moisture flux give evidence in the wet cases of inflow from the north-east, in conjunction with a ridging anticyclone south of the continent. In dry cases the trajectory of flow is north-westerly and the supply of moisture is limited. In the ECMWF composite maps of vertical motion, lift is weak over the interior in dry cases consistent with a gentle slope in the divergence profile. For wet cases upward motions are intense and widespread over the interior consistent with a steep slope in the divergence profile, and compensated by descending motions over the adjacent oceans along 30° S band. Precipitation in wet events is a combination of dynamical forcing, prefrontal moisture and unstable lower troposphere. In dry events, precursor moist inflow is limited, weak instability and, a gentle slope in the divergence/convergence fields are not conducive to sustain lift.
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Uren, Sally Clare. "The effects of wet and dry deposited ammonia on Calluna vulgaris." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/8895.
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Driejana, Ir. "Wet and dry deposition in the Derbyshire Peak District, Northern England." Thesis, Manchester Metropolitan University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390785.
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VILLELA, MARCOS JOSE REI. "TEMPERATURE BEHAVIOR ANALYSIS OF OIL PRODUCTION SYSTEMS: DRY AND WET COMPLETION COMPARISON." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6084@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCerca de 50 por cento das reservas brasileiras de hidrocarbonetos estão localizadas na plataforma continental em lâminas de água superiores a mil metros. As temperaturas congelantes do fundo do mar tornam os problemas inerentes ao escoamento da produção de petróleo, ainda mais críticos. Entretanto, os desafios da garantia de escoamento, não são os únicos obstáculos para a produção de petróleo em águas ultra-profundas. Além dos aspectos relacionados à geologia e fatores econômicos, a decisão de desenvolvimento de um campo de petróleo no mar, adotando completação submarina ou seca, precisa ser respaldada por uma análise criteriosa dos problemas relacionados com a garantia de escoamento, principalmente em locações de águas profundas e ultra- profundas. Nestes cenários, a maior variação da energia potencial e conseqüente intensificação do efeito Joule-Thomson, contribuem de uma forma bem mais significativa para a queda de temperatura e pressão. Este trabalho objetiva promover a comparação entre um sistema de produção usando poços direcionais de grande afastamento, produzindo para uma unidade de completação seca e um sistema adotando poços com completação submarina, a 850, 1.550 e 2.300m de lâmina de água, avaliando os efeitos das perdas de carga e calor em um fluxo multifásico. Com o uso de completação molhada, é avaliada a máxima distância viável entre a zona produtora e a plataforma de produção, de forma a permitir o fluxo de hidrocarbonetos sem formação de cristais de parafina. Com base nos resultados alcançados, podemos tirar algumas conclusões importantes quanto à tendência dos sistemas de produção em águas profundas e ultra- profundas, que nortearão no futuro próximo o desenvolvimento de campos de petróleo na plataforma continental brasileira.
Around 50 percent of the Brazilian reserves of hydrocarbons are located in the continental platform in water depths with more than one thousand meters. The freezing temperatures of the sea bottom make problems related to oil production, even more critical. However, the flow assurance challenges are not the only obstacles for the oil production in ultra-deep waters. Besides the aspects related to the geology and economical factors, the decision of development of an offshore oil field adopting a system with wet completion or with dry completion, needs to be supported by discerning analyses of the problems related to flow assurance aspects, mainly in deep and ultra-deep water locations. In these scenarios, a larger variation of the potential energy and consequent intensification of the Joule-Thomson effect, contribute in a much more significant way to the temperature and pressure drops. This work aims to promote the comparison between an oil production system using extended reach wells with a dry completion unit and another system with wet completion, at 850, 1.550 and 2.300m of water depth, evaluating the effects of pressure drop and heat loss in a multiphase flow. Using wet completion, it is evaluated the maximum feasible distances between the producing zone of the formation and the floating production unit, allowing the flow of hydrocarbons without interruption by the formation of paraffin crystals. Based on the reached results, we can reach some important conclusions regarding trend of production systems in deep and ultra-deep water, that will guide the development of oil fields in the near future in the Brazilian continental platform.
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Caldini, Nayara Nunes. "Use of bioflocs biomass wet and dry for feeding of Nile tilapia." Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=14408.
Full textAbstract:
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoThis study consisted of two experiments. The first objective was to demonstrate the technical feasibility of separate BFT tank technology in juvenile cultivation of Nile tilapia, for monitoring quality variables of water and productive performance. The fish were fed different combinations of artificial food (balanced diet) and natural food (bioflocs biomass). As the supply of food decreased the tanks increased the biomass supply bioflocs. Bioflocs biomass was produced in an external tank 500 L, separately from the cultivation system (separate tank BFT). You can reduce the regular feeding rates of juvenile Nile tilapia, with artificial diets, 25 %, without losses, if bioflocs to provide wet grown animals, as a food supplement, in equal proportion. The second objective was determine the effects of the provision of dried bioflocs biomass to Nile tilapia juveniles, stocked in experimental rearing tanks for 8 weeks, upon selected variables of water quality, growth performance and effluents quality. Fish was fed with different combinations of artificial diets and bioflocs biomass, in the wet form (in natura) or dried. As the supply of artificial diet was decreased, the provision of bioflocs biomass was increased in the same proportion. The bioflocs biomass was produced in two extra 500-L tanks. The growth performance of fish that were partially fed with dried bioflocs biomass has remained below what was observed in the tanks supplied with the wet bioflocs biomass. Due to the lacking of positive results, there is not any rationale to dry the bacterial bioflocs aiming at the delivery of it as a dried biomass to the cultured fish.
O presente estudo foi constituÃdo por dois experimentos completos e consecutivos. No primeiro, objetivou-se demonstrar a viabilidade tÃcnica da tecnologia do tanque BFT (c/bioflocos) avulso no cultivo de juvenis de tilÃpia do Nilo, pelo monitoramento de variÃveis de qualidade de Ãgua e de desempenho produtivo. Os peixes foram alimentados com diferentes combinaÃÃes de alimento artificial (raÃÃo balanceada) e de alimento natural (biomassa de bioflocos). à medida que diminuÃa o aporte de raÃÃo aos tanques, aumentava o fornecimento de biomassa de bioflocos. A biomassa de bioflocos foi produzida em um tanque externo de 500 L, em separado do sistema de cultivo (tanque BFT avulso). Os tanques de cultivo que receberam aplicaÃÃes diÃrias de bioflocos apresentaram concentraÃÃes de nitrito na Ãgua significativamente menores do que as observadas nos tanques nos quais a Ãnica fonte de alimentaÃÃo dos peixes foi a raÃÃo comercial. Concluiu-se que à possÃvel reduzir as taxas regulares de arraÃoamento de juvenis de tilÃpia do Nilo, com raÃÃes artificiais, em 25%, sem prejuÃzo zootÃcnico, caso se forneÃa bioflocos Ãmidos aos animais cultivados, como suplemento alimentar, em igual proporÃÃo. O segundo experimento teve como objetivo determinar os efeitos do fornecimento de biomassa seca de bioflocos a juvenis de tilÃpia do Nilo, mantidos em tanques experimentais de cultivo por oito semanas, sobre variÃveis selecionadas de qualidade de Ãgua, desempenho zootÃcnico e qualidade de efluentes. Os peixes foram alimentados com diferentes combinaÃÃes de raÃÃo balanceada e biomassa de bioflocos, na forma Ãmida (in natura) ou seca. à medida o aporte de raÃÃo aos tanques foi menor, o fornecimento de biomassa de bioflocos foi proporcionalmente maior. A biomassa de bioflocos foi produzida em dois tanques avulsos de 500 L. O desempenho zootÃcnico dos peixes nos tanques que receberam a suplementaÃÃo de biomassa seca de bioflocos ficou abaixo do observado nos tanques com biomassa Ãmida. Pela ausÃncia de resultados positivos, concluiu-se que nÃo hà justificativa tÃcnica para a secagem dos bioflocos bacterianos com o objetivo de fornecer a biomassa seca aos peixes cultivados
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Kerr, Kent. "Sampling for Beryllium Surface Contamination using Wet, Dry and Alcohol Wipe Sampling." Washington, D.C. : Oak Ridge, Tenn. : United States. National Nuclear Security Administration ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/837587-M4P95G/native/.
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Thesis (M.S.); Submitted to Central Missouri State University, Warrensburg, MO (US); 17 Dec 2004.Published through the Information Bridge: DOE Scientific and Technical Information. Kerr, Kent. NNSA Kansas City Site Office (US) NNSA Kansas City Site Office. 12/17/2004. Report is also available in paper and microfiche from NTIS.
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Goode, James Bruce. "Transitioning of spent advanced gas reactor fuel from wet to dry storage." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/20585/.
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Upon removal from a reactor spent nuclear fuel is placed into water storage for a period of time since water provides both a decay heat sink and radiation shielding. In the UK this fuel has traditionally been reprocessed however the decision has been made that this will cease in 2018 in favour of an open fuel cycle and direct disposal to a degological disposal facility, although this is not expected to be available until 2075. Current experience with pond storage has found that fuel can be safely stored in caustic dosed ponds for at least 25 years and therefore the current plan is to extend water storage until around 2040, however how the fuel will be stored for the remaining 35 years is yet to be decided. One option that is being considered is the use of dry storage which is being used successfully in the USA for the storage of fuel from Light Water Reactors. One of the most important factors when utilising dry stores is an effective drying step and this PhD is aiming to look at this area in particular. Commercial drying methods have been developed for use with Zircaloy and aluminium clad fuels however this PhD intends to develop a method that can be used to dry Stainless Steel clad fuels such as those used in the UK's Advanced Gas Reactors (AGR). Since intact AGR fuel has yet to be examined following storage the first part if this thesis looked at preparing samples for later macro scale testing. Samples were treated to induce defects known to be of concern and analysed with the conclusion being that bound water is of no concern for drying operations and can be disregarded when preparing samples. Since AGR is known to have failed by stress corrosion cracking water trapped within microcracked pins is a likely issue. A section of tube was prepared by compression and boiling in magnesium chloride which micro CT imaging found to have images of a similar size to known failures. This tube was prepared into a test piece for later testing. The second part of the thesis looks at macro scale testing using the test piece described above and a similar test piece with a 300 um pinhole. A multipurpose drying rig capable of vacuum drying and flowed gas drying was constructed. In the first phase of drying tests vacuum drying and flowed gas drying were compared using a test piece with a 300 um pinhole and the impact of different cover gas was assessed. vacuum drying was found to be significantly more effective than flowed gas drying with the type of cover gas having little impact. Most importantly this work guided further improvements to the rig. The second phase of this work carried out more detailed drying tests on vacuum drying and flowed gas drying and utilised the pinholed and cracked test piece. The greatest influencing factor on the drying rate (the rate at which water could be removed from inside the test piece) was found to be the water level inside the test piece with broadly similar rates being found in all conditions and with both test piece when the test piece was full. As the water level within the test piece dropped, vacuum drying quickly became more effective. This was not helped by considering energy usage. There was however a feeling that flowed gas drying was limited due to the pipework size. In the final phase of testing the ability to detect the point which all water was removed (the end point) from the test piece using online instrumentation was assessed. Currently a vacuum rebound test is used which is both time consuming and if flowed gas drying is being used requires additional plant equipment. It was found that dew point measurements appeared to give a relatively clear indication of the end point when for both vacuum drying and flowed gas drying. For vacuum drying only the measurement of mass flow and pressure also gave a reasonable indication of end point.
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Vaishampayan, Deep. "Dielectric Spectroscopy of Bisphenol A Epoxy Resin Aged in Wet and Dry Conditions." Thesis, Norwegian University of Science and Technology, Department of Electrical Power Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9932.
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This thesis presents the laboratory test data on Bisphenol A epoxy insulation.This thesis work deals with electrical, mechanical and thermal analysis of Bisphenol A epoxy resin. The main aim of this thesis work was to examine if dry and wet aging changes the glass transition temperature (Tg) of the epoxies and measure the impact on the complex permittivity under different ageing conditions namely dry and wet. During ageing the samples (epoxy discs and dog bones) were kept in water at 20°C, 45°C and 80°C both in dry and wet conditions for a period of one month. After the samples were removed from ageing they were conditioned in a vacuum oven for one week. The effect of temperature and relative humidity on unaged epoxy i.e. dry characterization was determined by keeping the samples in climate chamber with 15%RH (Relative Humidity) and temperatures 20°C, 45°C and 80°C. The wet characterization was carried out with 90%RH and temperatures 20°C, 45°C and 80°C. The surface of these samples was painted with silver paint (electrodes). Two circular discs were used for dielectric response measurement and 2 rectangular pieces for water sorption measurement. The dielectric response was measured when equilibrium/saturation condition was achieved. The dielectric response was measured in the frequency range from 0.01 Hz to 1000 Hz at 200 volts (peak). The wet characterization showed increases with aging temperature. The dielectric loss was also increasing with the temperature. It can be deduced that the water uptake by the epoxy increases with increase in humidity and temperature. The dry characterization showed and has steady growth with aging temperature. Therefore it can be deduced that characterization done in dry condition didnt significantly affect the complex permittivity as compared with wet characterization. The glass transition temperature (Tg) of the samples were found using DSC (Differential Scanning Calorimetry) with a heating rate 20°C/min. The Tg was measured in the samples in dry condition before the water absorption process, then in samples after the water absorption process with moisture in the sample, and then in sample after the desorption. The effect of water on the Tg of the epoxy polymer was studied. Tg was increasing with aging temperature, for both dry as well as wet samples. The increase in the value can be mainly attributed to post curing process of the epoxy. The mechanical strength of the epoxy was studied by applying a tensile force to the dog bone shaped samples till breakdown and the stress versus strain curve was detected. This test was also performed on the dry aged sample before water absorption, then in sample which was kept under water at 20°C ,45°C and 80°C for absorption, and in sample which has undergone absorption and desorption at 20°C ,45°C and 80°C. The difference between the stress-strain curves was documented and discussed. The ageing temperature plays a significant role in reducing the value of stress and percentage strain at max. For dry aged epoxy, stress reduces around 14% from 200C to 800C. However for wet aged epoxy samples tensile strength reduces around 25%. For dry aged samples % strain reduces around 0,3 %. and for wet aged samples it reduces around 0,5%.
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Lodhia, Prashant Twomey Janet. "A macro level environmental performance comparison dry machining process vs wet machining process /." Diss., A link to full text of this thesis in SOAR, 2007. http://soar.wichita.edu/dspace/handle/10057/1146.
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Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering."May 2007." Title from PDF title page (viewed on Dec. 27, 2007). Thesis adviser: Janet Twomey. Includes bibliographic references (leaves 52-54).
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Lineton, Warran Boyd. "An investigation into dry and wet textile friction and lubrication in practical applications." Thesis, De Montfort University, 1999. http://hdl.handle.net/2086/10707.
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The lubrication of dry viscose fibres by a two component finish, and the lubrication of wet Iyocell fabric against metal, with various aqueous lubricant systems, has been studied. Secondary ion mass spectrometry (SIMS) was investigated as a means of providing direct chemical information from finished fibre surfaces. The composition and distribution of a two component finish applied to viscose fibres was determined successfully. When applying finish from a bath, the surface composition of the finished fibres was not controlled by the bath conditions. Increasing the concentration of finish in the bath did, however, increase the total amount of finish deposited, and increasing the concentration of antistat relative to lubricant in the bath increased the amount of antistat relative to lubricant deposited on the finished fibres. Fibre friction was determined using the capstan method. The friction forces, measured for finished viscose fibres, were correlated with the finish application conditions. Increasing the emulsion concentration in the finish bath reduced fibre/metal friction, but finish component ratio, emulsion concentration, dip time and bath temperature did not affect fibre/fibre friction. Spray applying the finish resulted in unfinished regions on the fibre surfaces and the electrical resistance of fibre bundles was not reduced. Bath application of finish did lower electrical resistance in comparison with unfinished fibre, but none of the bath deposition variables had a significant effect on electrical resistance.
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Mahmoodabadi, Majid. "KOREAN ANTHRACITE COAL CLEANING BY MEANS OF DRY AND WET BASED SEPARATION TECHNOLOGIES." UKnowledge, 2015. http://uknowledge.uky.edu/mng_etds/18.
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Korean coals are typically high rank anthracite characterized by high ash content and difficult cleaning characteristics. The main objective of the study was to evaluate the feasibility of treating various size fractions within the coal using an assortment of physical coal cleaning technologies. Dry cleaning is preferred due to the friability of the coal. As such, three pneumatic processes were tested including Ore Sorting for the plus 10 mm material, Air Table Separation for 10 x 1 mm fraction and Tribo-electric Separator for - 1 mm fraction. The Dense Medium Cyclone is known to be one of the most efficient separation processes and thus was evaluated for the cleaning of 10 x 1 mm coal.
To realize the optimum performances from the Air Table and Rotary Tribo-electric Separator, their operational variables were systematically studied using a parametric experimental design. In addition, the dense medium cyclone and X-ray Transmission Sorting trials were performed under various medium densities and separation settings, respectively. A comparison of the cleaning performance revealed that the Dense Medium Cyclone and X-ray Transmission Sorting proved to provide the most effective results with maximum ash rejection and combustible recovery. The tribo-electric separation process was ineffective while the air table provided modest ash reduction potential.
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Anderson, Neil Raymond. "Evaluation of the performance characteristics of a hybrid (dry/wet) induced draft dephlegmator." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96105.
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Thesis (MEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: A novel induced draft hybrid (dry/wet) dephlegmator (HDWD) is introduced which can enhance the performance of dry air-cooled condenser systems and a model is developed to simulate its performance. The HDWD consists of two stages of cooling with the steam flow in series and the air flow in parallel through both stages. The first stage consists of downwardly inclined finned tube bundles, similar to conventional air-cooled condenser bundles, and the second stage comprises horizontal bare tube bundles of which the outer surface can selectively be operated dry or wet by spraying it with deluge water. A comparison of the HDWD with other existing and new concepts reveals the significant advantages that this technology has over other technologies. This thesis is a continuation of the work done by Heyns (2008), who introduced a forced draft HDWD and investigated its performance, and Owen (2013), who conducted a parametric investigation on the induced draft HDWD to improve the basic design proposed by Heyns (2008). In his thermo-flow model, Heyns (2008) conducted a thermal analysis assuming equal air flow through both stages and a constant vapor temperature inside the bundles, while Owen (2013) solved the thermal, steam-side pressure drop and draft equations. Both their models make use of empirical correlations by Gaddis & Gnielinski (1985), Zukauskas (1987), Mizushina et al. (1967) and Niitsu et al. (1967) for the performance characteristics. The current model solves the thermal, steam-side pressure drop and draft equations of the HDWD with better accuracy in the steam-side pressure drop calculation. The airside heat and mass transfer and loss coefficient correlations found in literature were found to deviate significantly from each other resulting in uncertainty regarding their suitability. Based on the recommendations by Owen (2013), a bare tube test bundle with 19 mm outer diameter tubes arranged with a triangular pitch of 38 mm is therefore designed, manufactured and tested to investigate the performance characteristics of the bundle experimentally under dry and wet operating conditions to evaluate the correlations from literature. The experimental data confirmed the applicability of the correlations of Gaddis & Gnielinski (1985) and Zukauskas (1987) to predict the dry HDWD performance, since they deviated by 7% and 5% respectively from the experimental data in die applicable range. The heat transfer during wet operation is slightly over estimated within 5% with the correlations of Mizushina et al. (1967) in the range of application. The air-side pressure drop during wet operation is underestimated by 29 to 39% by Niitsu et al. (1967) and the correlation obtained from the experimental results is therefore used in the current model. Using the current HDWD model indicates significant performance enhancement using tubes with a smaller diameter in the delugeable bundle compared to the larger tubes of Heyns (2008) and agrees very well with the model of Owen (2013).
AFRIKAANSE OPSOMMING: ‘n Hibriede geïnduseerde trek deflegmator is voorgestel wat die werksverrigting van huidige lugverkoelde kondenserstelsels kan verbeter en ‘n model is ontwikkel wat die werksverrigting simuleer. Die deflegmator bestaan uit twee stadiums van verkoeling met die stoomvloei in serie en die lugvloei in parallel deur beide stadia. Die eerste stadium bestaan uit skuins, afwaartse finbuisbundels, soortgelyk aan konvensionele lugverkoelde kondenser-finbuisbundels, en die tweede stadium bestaan uit horisontale kaalbuisbundels waarvan die buite-oppervlak selektief droog of nat bedryf kan word deur dit met verkoelingswater te benat. ‘n Vergelyking tussen die deflegmator en ander huidige en nuwe konsepte toon merkbare voordele wat die tegnologie bo die ander tegnologië het. Die tesis is ‘n voortsetting van die werk van Heyns (2008), wie ‘n hibriede geforseerde trek deflegmator voorgestel en die werksverrigting daarvan ondersoek het, en Owen (2013) wat ‘n parametriese studie op die hibriede geïnduseerde trek deflegmator gedoen het om die basiese ontwerp voorgestel deur Heyns (2008) te verbeter. In sy termovloei-model, het Heyns (2008) die termiese analise ondersoek met die aanname van gelyke hoeveelhede lugvloei deur beide stadia met ‘n konstante damp-temperatuur binne die bundels, terwyl Owen (2013) die termiese, stoomkant-drukval and trekvergelykings opgelos het. Beide hul modelle maak van die empiriese korrelasies van Gaddis & Gnielinski (1985), Zukauskas (1987), Mizushina et al. (1967) en Niitsu et al. (1967) gebruik vir die werkverrigtingskarakteristieke. Die huidige model los die termiese, die stoomkant-drukval asook die trekvergelykings van die deflegmator op met verbeterde akkuraatheid van die stoomkant-drukval berekeninge. Die lugkant warmte- en massaoordrag en verlieskoëffisiënt korrelasies wyk baie van mekaar af wat lei tot onsekerhede rakende hul toepasbaarheid. Gebaseer op die voorstelle van Owen (2013) is ‘n kaalbuisbundel met 19 mm buite-diameter buise met ‘n driehoekige steek van 38 mm dus ontwerp, vervaardig en getoets om die werksverrigtingskarakteristieke van die bundel eskperimenteel te ondersoek onder droë en nat toestande om die korrelasies van die literatuur te evalueer. Die eksperimentele data bevestig die toepaslikheid van die korrelasies van Gaddis & Gnielinski (1985) en Zukauskas (1987) om die droë werksverrigting van die deflegmator te voorspel, aangesien hul met 7% en 5% onderskeidelik afwyk van die eksperimentele data in die toepaslike bestek. Die warmteoordrag tydens natwerking is ietwat oorskat binne 5% met die korrelasies van Mizushina et al. (1967) in die bestek van toepassing. Die lugkant-drukval tydens natwerking is onderskat met 29 tot 39% deur Niitsu et al. (1967) en die korrelasie verkry vanaf die eksperimentele resultate is dus gebruik in die huidige model. Deur gebruik te maak van die huidige model van die deflegmator dui merkbare werksverrigting verbetering aan deur van buise met ‘n kleiner diameter in die benatbare bundel te gebruik in vergelyking met die groter buise van Heyns (2008) en stem baie goed ooreen met die model van Owen (2013).
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Wenzl, Jennifer [Verfasser]. "Wet and dry model granulates under mechanical load : a confocal microscopy study / Jennifer Wenzl." Mainz : Universitätsbibliothek Mainz, 2014. http://d-nb.info/1049672674/34.
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Young, Garth William II. "Evaluation of Friction Stir Processing of HY-80 Steel Under Wet and Dry Conditions." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/6892.
Full textAbstract:
This thesis describes the microstructural and mechanical property changes associated with Friction Stir Processing
(FSP) of HY-80 steel under dry and underwater conditions. HY-80 is a low-carbon alloy steel that is used in a
quenched and tempered condition and is highly susceptible to hydrogen assisted cracking associated with
conventional fusion welding. FSW/P (400 RPM/ 2 IPM) was conducted using a polycrystalline cubic boron nitride
tool having a pin length of 6.35 mm. Two sets of processing runs were completed on HY-80 plates, 6.35 mm in
thickness, one dry and the other under seawater. Analysis of the residual hydrogen content revealed little change in
hydrogen content associated with FSW/P. Detailed microstructural characterization (optical and scanning electron
microscopy) with emphasis on the differences in the distribution of constituent phases in the rolling, transverse and
normal planes was carried out. Microstructural analysis of the “plan-view” section at the tool extraction sites of
FSW/P samples was executed. Mechanical properties of these samples were evaluated by tensile, microhardness, and
Charpy V-notch impact resistance tests. The results indicated that austenitization occurred within the stir zones and
subsequent cooling influenced the final microstructure and properties. The thermomechanically affected zone
displayed a gradual change in near-equiaxed austenitic grain size towards both the tool axis as well as the base plate
with little grain shape change throughout. These results have been rationalized on the basis of expected temperature
and deformation fields generated setup in these steel samples and the nature of phase transformations occurring in low
carbon steels such as HY-80.
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CAC, FRANKY EDUARDO REYES. "METROLOGICAL ANALYSIS OF THE TRANSIENT BEHAVIOR OF A WET BULB AND DRY BULB PSYCHROMETER." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6718@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROEste trabalho apresenta um estudo do comportamento transiente de um medidor de umidade tipo bulbo úmido e bulbo seco, assim como a determinação da umidade do ar em diferentes condições ambientais, que foram simuladas em laboratório. O psicrômetro do tipo bulbo úmido e bulbo seco é amplamente utilizado na indústria de ar condicionado, na monitoração da umidade em ambientes fechados, nas estações de meteorologia para a monitoração da umidade da atmosfera, e na prevenção das condições climáticas. Para o desenvolvimento do presente trabalho, foi construído um psicrômetro do tipo bulbo úmido e bulbo seco de ar aspirado, utilizando dois termômetros separados por uma placa de acrílico. Os termômetros utilizados foram tipo PT-100 e tipo Termopar. Na avaliação do conteúdo de umidade do ar, foi utilizada a medição de temperatura registrada por dois termômetros que compõem o psicrômetro, onde um deles registra a temperatura do ar que incide sobre o psicrômetro e serve como referência; e o segundo termômetro, recoberto com uma mecha molhada com água destilada, registra uma temperatura mais baixa devido ao fenômeno de resfriamento evaporativo, o qual é conseqüência da transferência de calor e massa entre a mecha molhada e o ar forçado a passar através dela. Na avaliação do comportamento transiente do psicrômetro, foram aplicados diferentes modelos de ajuste aos dados experimentais, procurando aquele que melhor representasse o comportamento através do tempo do termômetro bulbo úmido. Entre os modelos de ajuste estão: o linear, o exponencial, a soma de dois exponenciais, o racional, o polinomial de grau 6 e o exponencial linear (soma de exponencial com linha reta). A cada um dos modelos foi aplicado o método dos mínimos quadrados, e foi determinado por meio do critério de Akaike que o modelo exponencial linear é o melhor modelo de ajuste. As incertezas das constantes dos diferentes modelos de ajuste foram calculadas através do método das diferenças finitas. São apresentados os valores das constantes de tempo para diferentes valores de velocidade do ar e diferentes graus de umidade, tanto para os termômetros PT-100 quanto para o tipo Termopar. Finalmente, são apresentados os resultados da aplicação da regressão linear múltipla entre as constantes de tempo, a velocidade e a umidade do ar, tanto para o psicrômetro baseado nos termômetros tipo PT-100 quanto nos termômetros tipo Termopar. A presente pesquisa de mestrado contribui para o desenvolvimento da metrologia térmica no Brasil.
This work presents a study of the transient behavior of a wet bulb and dry bulb psychrometer, as well as the determination of the humidity of air under different environment conditions. The wet bulb and dry bulb psychrometer are widely used in the air conditioning industry, for monitoring the humidity in closed environments, and in meteorology stations for the monitoring the atmosphere humidity and in the prevention of the climatic conditions. For the development of the present work, a wet bulb and dry bulb aspirated psychrometer was built, using two thermometers, which are physically separated by an acrylic plate. Two types of thermometers were used: PT-100 and Thermocouple. In the evaluation of the humidity content, the measurement of temperature was been registered by two thermometers (used as the psychrometer components), where one of them registers the temperature of the air that impacts the psychrometer and serves as reference; and the other one covered by a wick wet with distilled water, registers a lower temperature due to the phenomenon of evaporative cooling, which is a consequence of the mass transfer between the wet wick and the air that is forced to pass through it. In the evaluation of the transient behavior of the psychrometer different models of adjustment to the experimental data have been applied, seeking the best theoretical model that represented the behaviour through the time of the humid bulb thermometer. Among the adjustment models are: the linear one, the exponential one, the addition of two exponential ones, the rational one, polynomial of exponential degree 6 and the linear one (which adds the exponential curve and the straight line). For each of the models the method of the minimum square had been applied, and it was found by means of the of Aikaike´s criterion that the linear exponential model is the best one. The uncertainties of the constants of the different models of adjustment were calculated through the method of the finite differences. The values of the time constants of time for different values of air speed and different degrees of humidity for both thermometers PT-100 and Thermocouple type had been presented. Finally, the results of the application of the multiple linear regression are presented among the time constants, the speed, and the humidity of air for both psychrometer based on the thermometers PT- 100 type and the thermometers Thermocouple type. This MSc research contributes towards the development of the thermal metrology in Brazil.
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Ho, Genevieve Edine. "Analysis of wet & dry weather bacterial concentrations within Kranji & Marina Catchments, Singapore." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66833.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 75-79).
The Singaporean government's Public Utilities Board aims to open Kranji and Marina Reservoirs to the public for recreational use. Thus, the water bodies have to be safe from fecal contamination in order to protect the people's health during water-contact activities. Under the Singapore-MIT Alliance for Research and Technology (SMART) program, faculty and students from Nanyang Technological University and MIT have worked together to conduct bacteriological studies at both Kranji and Marina catchments and their reservoirs. Storm water, especially from urban landscapes, contains elevated concentrations of total coliform, . coli, and enterococci bacteria. The goal of this study was to review, classify, and evaluate wet- and dryweather bacteria samples dating back to 2005 with a focus on grab-samples collected by Nshimyimana (2010) in 2009 and samples collected during January 2011 field work at Choa Chu Kang Crescent, Bras Basah, and Verde. These bacteriological samples were collected from high density residential (HDR), low density residential, forested, and commercial areas. Evaluation of the relationship between concentration and flow showed a linear increase in bacteria concentrations with flow in storm water from mixed forested and HDR areas, a pattern that is consistent with nonpoint source runoff, while commercial areas exhibited peak concentrations during low and high, but not intermediate, flows indicating contributions from both nonpoint and point sources. Likely point sources are sanitary sewer leakage due to aging infrastructure in the commercial area. All measured concentrations exceeded Singapore and USEPA's recommended bacterial levels for recreational water. Hence, more wet-weather sampling is recommended in order to collect data on bacterial concentrations so that more robust statistical analyses can be performed in future studies. The elevated bacterial concentrations during wet weather from this study indicate that extra precaution should be taken to manage discharge of storm water into receiving waters before they are made accessible to the public.
by Genevieve Edine Ho.
M.Eng.
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Heyns, Johan Adam. "Performance characteristics of an air-cooled steam condenser incorporating a hybrid (dry/wet) dephlegmator." Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/350.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008.This study evaluates the performance characteristics of a power plant incorporating a steam turbine and a direct air-cooled dry/wet condenser operating at different ambient temperatures. The proposed cooling system uses existing A-frame air-cooled condenser (ACC) technology and through the introduction of a hybrid (dry/wet) dephiegmator achieves measurable enhancement in cooling performance when temperatures are high. In order to determine the thermal-flow performance characteristics of the wet section of the dephlegmator, tests are conducted on an evaporative cooler. From the experimental results, correlations for the water film heat transfer coefficient, air-water mass transfer coefficient and the air-side pressure drop over a deluged tube bundle are developed. During periods of high ambient temperatures the hybrid (dry/wet) condenser operating in a wet mode can achieve the same increased turbine performance as an oversized air-cooled condenser or an air-cooled condenser rith adiabatic cooling (spray cooling) of the inlet air at a considerably lower cost. For the same turbine power output the water consumed by an air-cooled condenser incorporating a hybrid (dry/wet) dephlegmator is at least 20% less than an air- cooled condenser with adiabatic cooling of the inlet air.
Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University
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Falloon, S. S. "An experimental study of friction between wet and dry human skin and nonwoven fabrics." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1458878/.
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Many people who have urinary incontinence manage it with the use of absorbent hygiene products, such as pads. Long-term use of these products can lead to abrasion by friction between the topsheet (a nonwoven fabric) and the skin, and is exacerbated when the skin is wet. However, the nature and mechanisms of friction between skin and nonwovens are poorly understood, hindering progress to improve products. Most work on skin friction to date has involved the use of skin surrogates or real skin in the dry state only. Moreover, only a narrow range of different nonwoven fabrics have been investigated. The work described in this thesis aimed to improve understanding of friction between nonwoven fabrics and human skin, and was divided into four main blocks. In the first, friction was measured between a skin surrogate (Lorica Soft) and 13 different nonwoven fabrics, varying in structure, fibre material and manufacturing techniques. Amontons’ law was closely obeyed for all nonwovens (that is, coefficients of friction were independent of normal force) and the data were used to select a representative subset of five nonwovens for subsequent work. In the second block of work, an in vivo study of friction was conducted between the subset of (five) nonwovens and the dry volar forearm skin of 19 female volunteers (aged 20-95 years). It was found that Amontons’ law also held for all of these measurements, despite the general viscoelastic nature of human skin, the range of skin types (from smooth and firm to wrinkled and flaccid) and the difference in ages. The coefficient of friction for a given fabric varied considerably between participants (an increase of up to 101% of the lowest coefficient value), but the fabrics were generally ranked in the same order for all volunteers. The third block of work involved the measurement of wet friction between the subset of five nonwovens and volar forearm skin of five of the study participants. In general, the coefficient of friction increased with skin wetness/hydration by up to a factor of thirteen until the skin was damp/moist. The relationship for very wet skin (with surface water) – thought to be lubricated – was unclear and varied between participants and between nonwovens. However, further work would be required to locate and quantify the excess water in and on the skin, in order to more accurately evaluate the contribution of water to friction. Finally, in the fourth block of work, the fibre footprints of nonwovens against a surrogate skin surface (glass microscope slide) were examined, providing insight into how friction is mediated by the interface. Total fibre contact length was always extremely low (typically 0.3-1.6 mm · mm-2) and increased linearly with the log of pressure, usually due to an increase in the number of contacts and sometimes because of an increase in the lengths of existing fibre contacts.
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Kidanemariam, Mussie T. "Mechanisms for the wet and dry years over Eritrea during the summer rainfall season." Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/6978.
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Bibliography: leaves 54-57.The economy of Eritrea depends on rain-fed agriculture, which is highly sensitive to seasonal and inter-annual variations of rainfall. Adequate amount of rainfall is required every year for adequate agricultural production and drinking water. Therefore, the distribution of seasonal rainfall in space and time is critical to the country's economy. Drought has great influence on the socio-economic aspect and livelihood of the rural population. Drought occurs in Eritrea due to anomalous regional atmospheric circulation. This study focuses on the summer rainy season of June, July and August (JJA). It examines atmospheric and oceanographic mechanism patterns associated to summer rainfall anomalies. The investigation mainly concentrates on wet and dry spells that occurred over Eritrea during the rainy seasons (June to August) of 1950's-1990's. Rainfall data was available from the Climatic Research Unit (CRU) Hulme dataset for a period of 1950 -1996 and this together with rainfall data from the Africa Data Dissemination Service was used to determine the characteristics of wet and dry spells. Finally, NCEP-NCAR reanalysis climate data was used to analyse the atmospheric circulation associated with wet and dry years. It has been found that the pattern of the SST along the eastern Pacific and the Indian oceans seem to influence the occurrence of the anomaly rainfall years. Correlation analysis shows that Eritrean summer rainfall is more strongly correlated with the eastern Pacific and Indian Oceans SST. Thus, the drought records in Eritrea are mainly associated with EI Nino events.
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Broadley, Andrew. "Assessing the effect of water resource development on fisheries in the wet-dry tropics." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/405635.
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The growing demand for freshwater resources has led to dam construction and water diversions in a majority of the world’s large rivers. The regulation of river flows, coupled with changes to land use in and around coastal areas, has far-reaching consequences not only for the ecology of rivers but also for fisheries in marine ecosystems. The challenges of quantifying the influence of regulated flows on marine fish stocks is complicated by our poor understanding of how flow induced processes interact over spatial and temporal scales throughout a species life history. The life history of the banana prawn, Penaeus merguiensis, is an ideal template to assess the potential impact of river regulation on the catch of a commercial fishery. The banana prawn is an estuarine-dependent marine species that spawn offshore and use estuaries as nursery areas. This research will ask how water resource development in three northern Australian rivers, the Mitchell, Gilbert and Flinders Rivers, affects population dynamics and catch of banana prawns in the south-eastern Gulf of Carpentaria.
The extreme climatic variability in northern Australia raises concerns about how river regulation will impact marine fisheries. In Chapter 2, a spatio-temporal Bayesian modelwas developed to predict the impact of river regulation on the catch of banana prawns. The analyses of three river regulation scenarios found that catch was most impacted by river regulation during low flows. The impact of river regulation was greatest for a scenario with dams on the Mitchell River, where the model predicted catch would decline by 53% during a year with low flow. These results imply that maintenance of low-level flows is a crucial requirement for sustained fishery yields. Further, these findings suggest that water managers must balance the upstream demand for water during drier years against the impact on downstream prawn fisheries.
Banana prawns have complex life histories where survival in the early life stages is largely dependent on prevailing oceanic conditions. Chapter 3 evaluated the effects of river flows, wind, tides and currents on larval connectivity from spawning areas to estuarine nurseries. To identify patterns in larval connectivity the output from a high resolution three-dimensional Regional Oceanic Modelling System (ROMS) was coupled to Ichthyop, a biophysical Lagrangian particle tracking model. The probability of larvae transported from release zones to nursery areas was computed under different river flow and coastal current conditions. This research found that the importance of each river’s role as a nursery area changed throughout the season and depended on the timing of river flows and direction of coastal currents. Further, high river flow events, >5,500 m3 s-1, blocked post-larval ingress to estuarine nurseries altogether. A key outcome of this research was the development of an index of larval connectivity for each river to be used in a population model.
Alterations to the magnitude, timing and duration of flows can affect different life stages, either directly from an individual prawn’s biological response to changes in salinity or temperature, or indirectly by modifying habitat, movement patterns and the availability of food. In Chapter 4, a population dynamics model was developed to simulate the effect of different river flow regulation scenarios on larval, juvenile and adult life stages. Sensitivity analysis and Bayesian calibration were used to determine how uncertainty in key parameters were driving the variation in modelled results. The analyses of low and high flow scenarios found the contribution of juveniles from each nursery to the adult population was lower with increasing levels of water extracted. This key finding suggests maintaining historic mean flow levels during periods of low flow or drought will be critical to sustain juvenile production and fishery yield.
Overall, this research has demonstrated the dynamic and complex interaction between river flows and the life of banana prawns. The models developed provide an insight into how water resource development and the fishery would benefit from an integrated planning and management approach.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Leigh, Catherine. "Floodplain river function in Australia's wet/dry tropics, with specific reference to aquatic macroinvertebrates and the Gulf of Carpentaria." Thesis, Griffith University, 2009. https://eprints.qut.edu.au/119606/1/Leigh_2009_02Thesis.pdf.
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This thesis provides significant insight into our understanding of river function in highly seasonal systems. In north Australia’s vast wet/dry tropics, large rivers and associated wetlands are regarded among the continent’s most biologically diverse and ecologically healthy. Until recently however, research on the hydrology, biodiversity and function of Australian rivers has focussed on the south. My thesis investigates floodplain river function in Australia’s wet/dry tropics, more specifically in the Gulf of Carpentaria drainage division, and is the first to present a dynamic conceptual model of river function for these systems. Three major themes reside within riverine ecology: flow, pattern and process. These themes feature within existing conceptual models of large river function, for example, the River Continuum Concept, the Flood Pulse Concept and the Riverine Productivity Model. These themes and models were used as a template to explore river function in the study region: flow, as broad-scale hydrology and more localised hydrological connectivity; patterns, as spatiotemporal variation in aquatic macroinvertebrate biodiversity; and processes, as organic carbon flow through aquatic macroinvertebrate food webs. The flow regime is major driver of river function, and as such, a multivariate analysis of daily flow data from large, Gulf of Carpentaria rivers was conducted. Two major classes of river were found, each with a distinct flow regime type: ‘tropical’ rivers were characterised by flow regularity and permanent hydrological connection, ‘dryland’ rivers by high levels of flow variability and ephemerality, similar to rivers in Australia’s central and semi-arid zones. However, both river types experienced seasonal change, associated with higher flow magnitudes in the wet and lower flow magnitudes in the dry, with ‘dryland’ rivers typified by greater numbers of zero flow days. These features—flow regularity and permanence for ‘tropical’ rivers, flow variability and absence for ‘dryland’ rivers, and wet/dry seasonality for both river types—were proposed as the broad-scale hydrological drivers of river function in the Gulf region and are expected to be found as important drivers throughout the wet/dry tropics.
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Guan, Lan. "Wet-milling of waxy wheat flours and characteristics of waxy wheat starch." Thesis, Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/955.
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Benítez, Juan Manuel González. "Quantification of atmospheric water soluble inorganic and organic nitrogen." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4635.
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The key aims of this project were: (i) investigation of atmospheric nitrogen deposition, focused on discrimination between bulk, wet and dry deposition, and between particulate matter and gas phase, (ii) accurate quantification of the contributions of dissolved organic and inorganic nitrogen to each type of deposition, and (iii) exploration of the origin and potential sources of atmospheric water soluble organic nitrogen (WSON). This project was particularly focused on the WSON fraction because, despite it being a potentially important source of bioavailable reactive nitrogen, a number of questions regarding its deposition mechanism (wet vs. dry), composition and origin (natural, anthropogenic or mixed) remain unanswered. There are two major difficulties in WSON determination: (i) the diversity of organic nitrogen compounds compared with the inorganic forms, and (ii) the lack of a direct determination method: the derivation of organic nitrogen concentrations in an aqueous sample involves the determination of the dissolved inorganic nitrogen (DIN) species concentration, comprising nitrate and ammonium, the determination of the total dissolved nitrogen (TDN) concentration, and the subtraction of the DIN concentrations from the TDN concentration. TDN determination requires a preparatory digestion step: high-temperature catalytic oxidation was the method used in this study. Ion chromatography (IC) was the method of choice for nitrate determination, whilst ammonium determination was by IC for rain samples, and by flow injection analysis for air samples collected into aqueous media. This thesis is structured in 3 main parts: the first part examines weekly rain data over a period of 22 months from June 2005 to March 2007 collected in 2 types of rain collector (bulk deposition and “dry+wet” deposition) located in a semi-rural area 15 km southwest of Edinburgh, UK (N55°51′44″, W3°12′19″). Bulk deposition collectors were the standard rain gauges used in the UK national network for monitoring precipitation composition. “Dry+wet” deposition collectors were flushing rain gauges equipped with a rain detector, a spray nozzle, a 2-way valve and two independent bottles to collect funnel washings (dry deposition) and true wet deposition. A key objective in this part of the work was the accurate quantification of inorganic and organic water-soluble nitrogen species contribution to each type of deposition. On average, for the 27 weekly samples with 3 valid replicates for the 2 types of collectors, DON represented 23% of the TDN in bulk deposition. Dry deposition of particles and gas on the funnel surface, rather than rain, contributed over half of all N-containing species (inorganic and organic). Some discrepancies were found between bulk and flushing rain gauges, for deposition of both TDN and DON, suggesting biological conversion and loss of inorganic N in the flushing samplers. The second stage of this project was the investigation of in situ atmospheric concentrations of WSN species, both organic and inorganic. Simultaneous daily measurements of ammonium, nitrate and WSON were made between July and November 2008 at the same semi-rural site in south-east Scotland. Discrimination between material from the gas and particle phases was achieved by means of Cofer scrubbers and PTFE membrane filters, respectively. Average concentrations of NH3 (determined as NH4+), NO2/HNO3 (determined as NO3-) and WSON in the gas phase were 82 ± 54 nmol N m-3, 2.6 ± 2.5 nmol N m-3 and 18 ± 12 nmol N m-3 respectively, and in the particle phase were 20 ± 24 nmol N m-3, 10 ± 9 nmol N m-3 and 8 ± 7 nmol N m-3 respectively (± represent standard deviation across all valid daily samples, not error of triplicate samples). Except for oxidised inorganic N, average concentrations in the gas phase were larger than in the particle phase. No evidence of solely agricultural or solely combustion sources of WSON was found, as no correlation in either phase between WSON and either NH4+ or NO3- could be established. The final stage of this project was to gain a broader picture of nitrogen deposition across Europe. Rain samples were analysed for TDN and DIN from a network of 21 different sampling locations, from the south of Portugal to the north of Finland. The average DON contribution across the 21 sampling sites was ~ 19% and, according to the data gathered in this study, DON species appeared largely unrelated specifically to agricultural or to combustion nitrogen sources, although the results varied widely from site to site. Overall, this work has shown that ON and its deposition comprises a significant component of total atmospheric reactive nitrogen.
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Schofield, Jamie Rae. "Electrocardiogram Signal Quality Comparison Between A Dry Electrode and A Standard Wet Electrode over a Period of Extended Wear." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1334707695.
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Sinsheimer, Peter. "Fashioning a greener shade of clean integrating pollution prevention into public policy : the case of professional wet cleaning /." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1835200081&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Baars, Holger. "Aerosol profiling with lidar in the Amazon Basin during the wet and dry season 2008." Doctoral thesis, Universitätsbibliothek Leipzig, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-98757.
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Im Rahmen der vorliegenden Arbeit wurden die Eigenschaften von atmosphärischen Aerosolpartikeln im tropischen Regenwald des Amazonasgebietes bestimmt. Dazu wurden die Daten einer fast einjährigen Lidarmesskampagne ausgewertet und diskutiert. Die Messungen wurden mit einem automatischen Mehrwellenlängen-Polarisations-Raman-Lidar im zentralen Amazonasbecken nahe Manaus, Brasilien, im Zeitraum von Januar bis November 2008 durchgeführt. Somit konnten erstmalig optische und mikrophysikalische Aerosoleigenschaften im Amazonasgebiet während der Regenzeit (ca. Dezember-Mai) und Trockenzeit (ca. Juni-November) höhenaufgelöst charakterisiert werden. Einleitend werden die meteorologischen Bedingungen im Amazonasgebiet erläutert und eine Literaturübersicht über Aerosolforschung in dieser Region gegeben. Das Messgerät sowie verschiedene Kalibrier- und Korrekturschemen, die zur Datenauswertung notwendig sind, werden vorgestellt. Auch Vergleiche mit anderen Messgeräten werden diskutiert. Diese zeigen, dass die aus den Lidarmessungen abgeleiteten Parameter von hoher Qualität sind. Anhand von Fallstudien werden mit Hilfe von Rückwärtstrajektorien und Satellitenmessungen typische Aerosolbedingungen am Messstandort diskutiert. Um die generellen Unterschiede zwischen Regen- und Trockenzeit zu quantifizieren, wird eine statistische Auswertung aller analysierten Lidarmessungen präsentiert. Die Analyse der Lidardaten zeigt, dass während der Regenzeit im Amazonasgebiet in ca. der Hälfte aller Fälle sehr saubere Bedingungen mit einer Aerosol Optischen Dicke (AOD) von weniger als 0.05 (bei 532 nm) vorherrschen können. Allerdings wurde in ca. 30% aller analysierten Fälle im Zeitraum von Januar bis Mai auch afrikanisches Aerosol, vornehmlich Saharastaub und Biomasseverbrennungsaerosol (BBA), am Messstandort detektiert. Dabei dominierte meist BBA die Aerosolpopulation, wie die Depolarisationsmessungen zeigten. In der Trockenzeit ist die Atmosphäre im Amazonasbecken hauptsächlich mit BBA aus Südamerika belastet. Daher ist die AOD im Durchschnitt um einen Faktor drei größ er als in der Regenzeit. BBA wurde zu dieser Jahreszeit regelmäßig bis zu einer Höhe von 4-6 km detektiert. Basierend auf den vorgestellten Langzeitmessungen werden erstmalig die optischen Eigenschaften von südamerikanischem BBA statistisch analysiert und diskutiertContinuous lidar measurements were performed in the Amazon rain forest for almost one year in 2008. The results of the automated multiwavelength-Raman-polarization lidar observations were presented in this dissertation. These measurements are the first long-term observations of the vertical aerosol structure ever made in the Amazon Basin. The advanced lidar observations were conducted 60 km north of Manaus in the central northern part of Amazonia. The area is widely covered with pristine rain forest. A HYSPLIT backward-trajectory analysis showed that the observations were representative on a regional scale for the central northern part of the Amazon rain forest. The general weather conditions in this region are characterized by a wet (December-June) and a dry season (July-November). During the dry season, a high fire activity occurs in Amazonia, which heavily influences the atmospheric conditions. With the lidar instrument, vertical profiles of the particle backscatter coefficient at 355, 532, and 1064 nm, of the particle extinction coefficient at 355 and 532 nm, and of the particle linear depolarization ratio at 355 nm can be determined. The results from the long-term lidar observations performed in Brazil contain a lot of new information about the aerosol conditions in the central northern Amazon Basin and corroborate certain findings from former aerosol measurements in Amazonia. It was shown for the first time that advection of Saharan dust together with biomass burning aerosol (BBA) from Africa occurred regularly throughout the wet season. In about one third (32%) of all lidar observations during the wet season, African aerosol was dominating the optical aerosol properties in Amazonia. The analysis of the vertical aerosol structure during such events revealed that the African aerosol arriving in the central northern Amazon Basin was usually trapped in the lowermost 3-3.5 km of the troposphere. To quantify the amount of Saharan dust and African smoke transported towards the lidar site, the dust contribution to the measured optical aerosol properties was separated by means of the measured particle depolarization ratio. This study led to the result that in about one half of the cases with African aerosol advection, smoke particles contributed to more than 50% to the total Aerosol Optical Depth (AOD). The smoke transport from Africa towards Amazonia occurred predominantly between January and April when the fire activity in Central Africa was highest. BBA is thus a major constituent of the aerosol plumes that are regularly transported from Africa towards Amazonia. This is a key finding of the presented study. During clean conditions, an AOD (532 nm) of less than 0.05 was observed and the aerosol was trapped in the lowermost 2 km of the troposphere. However, the analysis of the long-term data set revealed that these clean atmospheric conditions occurred in only 48% of all wet-season cases. One example for such background conditions was intensively discussed and it was shown that a major meso-scale rain event occurred in the Amazon region at the same time. This precipitation event was possibly partly responsible for the very low aerosol load. Two case studies from the dry season were presented for which BBA dominated the optical properties. In the first case, a comparable high aerosol load (AOD of 0.41) prevailed while in the second one, a medium aerosol load (AOD of 0.15) was observed. Aged BBA advected from regions south of the lidar site were identified to be the dominant aerosol species for both cases. However, very different geometrical, optical and microphysical properties of BBA (e.g., vertical layering, lidar ratio, Ångström exponent, effective radius, SSA) were observed on both days. In the first case, aerosol was present up to about 4.5 km. Extinction-related Ångström exponent s of about 1 and lidar ratios between 70 and 90 sr were found at different heights for the smoke aerosol. The BBA was highly absorbing (SSA of 0.81) at heights of the highest RH (85%), whereas above under dry conditions (RH=50%) only moderate absorption (SSA of 0.93) was detected. In the second case, smoke was detected up to 4.5 km, and Ångström exponent of about 2 and lidar ratios of 45-55 sr were measured in the aerosol layers. The BBA was only moderately absorbing indicated by SSA values between 0.92 and 0.94. The reason for the differences in the smoke properties could be the shorter travel time to the lidar site (<24 h), different aging processes (e.g., cloud/rain processing), or different burning conditions. In both cases, no depolarizing effects of the BBA could be observed. The strong contrast between the aerosol conditions in the dry season and the wet season were confirmed by the statistical analysis of all lidar observations in 2008. Due to the high BBA concentration in the atmosphere, the mean AOD of the dry season was found to be a factor of 3 higher than the mean AOD of the wet season (0.26 compared to 0.08 at 532 nm). Maximum AOD values were less than 0.55 (at 532 nm) and hence show that the lidar location was not in the direct vicinity of fire events. In only 7% of all cases in the dry season 2008, an AOD below 0.1 was observed. Also the maximum extinction and backscatter coefficient values in the dry season 2008 were 2-3 times higher than during the wet season of this year. The vertical aerosol distributions differ also significantly between the two seasons. In the wet season, the aerosol was mostly trapped in the lowermost 2.5 km, while in the dry season aerosol typically reached up to 4.5 km. Aerosol was occasionally detected up to 6.14 km in the dry season. The majority of the aerosol (95% of the AOD), however, was found to be on average below 2.3 km in the wet season and below 3 km in the dry season. During the wet season, lofted aerosol layers and multiple aerosol stratification was less frequent than in the dry season. The extent of BBA plumes during the dry season showed no correlation to the ML top height. Virtually uniform smoke haze layers were observed up to the AL top. Thus, pyro-convection and/or cloud-related mixing seem to be the major processes for the vertical distribution of BBA
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Ankerfors, Caroline. "Polyelectrolyte complexes : Preparation, characterization, and use for control of wet and dry adhesion between surfaces." Doctoral thesis, KTH, Fiberteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-94138.
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This thesis examines polyelectrolyte complex (PEC) preparation, adsorption behaviour, and potential use for control of wet and dry adhesion between surfaces. PEC formation was studied using a jet-mixing method not previously used for mixing polyelectrolytes. The PECs were formed using various mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method. The results indicated that using the jet mixer allowed the size of the formed PECs to be controlled, which was not the case with the polyelectrolyte titration method, and a two-step mechanism for PEC formation was suggested. Adsorption experiments comparing two types of PECs, both produced from PAA and PAH, but with different molecular weights, demonstrated that surface-induced aggregation occurred in the high-molecular-weight PECs, whereas the adsorption stopped at a low level in the low-molecular-weight PECs. It was suggested that the latter PECs consisted of two fractions of complexes and that the fraction with lower polymer density exerted a site-blocking effect, hindering further adsorption. It was also demonstrated that particle-PECs (PPECs), in which one polyion was replaced with a silica nanoparticle, could be prepared. The purpose of preparing PPECs was to create a PEC structure that could create a joint with a special failure pattern referred to as disentanglement behaviour. Using the colloidal probe AFM technique, the expected disentanglement could be detected in PPECs, though the joint strength was low. Adhesion experiments demonstrated significantly higher pull-off values with polymer–polymer complexes than with PPECs. However, there was large spread in the data, possibly due to the surface inhomogeneity. Experiments using low-molecular-weight PECs as a paper strength agent demonstrated that PECs can indeed increase paper strength. Comparing the PEC results with those for polyelectrolyte multilayers (PEMs) prepared from the same polyelectrolytes indicated that, since the PEM strategy enables higher adsorption levels than does the PEC strategy, greater absolute strength improvements could be achieved using PEMs. However, PEC treatment resulted in the greatest effect per adsorbed amount of polymer.Denna avhandling behandlar tillverkning av polyelektrolytkomplex (PEC), deras adsorption och potentiella användning för att öka adhesionen mellan ytor i vått och torrt. PEC bildades med hjälp av jetmixningsmetoden, en metod som inte tidigare använts för PEC‑tillverkning. Resultaten av tillverkningen jämfördes med resultat för PEC bildade genom den tidigare ofta använda polyelektrolyttitreringsmetoden. Jämförelsen visade att med jetmixningsmetoden kunde storleken på de bildade PECen styras med hjälp av blandningstiden, något som inte var möjligt med polyelektrolyttitreringsmetoden. Utifrån resultaten föreslås en två-stegsmekanism för PEC-bildandet. Adsorptionsexperiment med två typer av PEC, båda tillverkade av PAA och PAH fast med olika molekylvikter, visade att för högmolekylära PEC skedde en ytinducerad aggregation, medan adsorptionen stannade på en låg nivå för de lågmolekylära PECen. De senare PECen antogs bestå av två olika fraktioner, av vilka en fraktion med lägre polymerdensitet föreslogs ha en ytblockerande effekt, och därigenom hindrades vidare adsorption. Det visades också att partikel-PEC (PPEC), där ena polymerkomponenten bytts ut mot anjoniska nanopartiklar av kiseloxid, kunde tillverkas. Syftet var att skapa strukturer som kan åstadkomma ett brottmönster med uttrassling mellan ytor. Med hjälp av kolloidalprobs-AFM (atomkraftsmikroskopi) kunde det önskade uttrasslingsbeteendet påvisas, men fogstyrkan var låg. Adhesionsexperiment med polymer-polymer-PEC visade på högre styrkor än PPECen, men också stor spridning i data, troligen på grund av inhomogenitet i ytornas struktur. Experiment där lågmolekylära PEC använts som styrkekemikalie för papper visade att tillsats av PEC kan öka pappersstyrkan. Jämförelse med resultat för polyelektrolytmultilager (PEM) av samma komponenter visade att eftersom högre adsorptionsnivåer kan uppnås med PEM så kan större styrkeökningar erhållas med PEM. Däremot visades att den högsta styrkeökningen per adsorberad mängd polymer erhölls med PEC-behandlingen.
QC 20120508
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Gitau, Wilson. "Diagnosis and predictability of intraseasonal characteristics of wet and dry spells over equatorial east Africa." Phd thesis, Université de Bourgogne, 2010. http://tel.archives-ouvertes.fr/tel-00794889.
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Most of Eastern Africa has arid and semi-arid climate with high space-time variability in rainfall. The droughts are very common in this region, and often persist for several years, preceded or followed by extreme floods. Most of the livelihoods and socio-economic activities however remain rain-dependent leading to severe negative impacts during the periods of occurrence of climate extremes. It has been noted that one extreme event was capable of reversing national economic growth made over a period of several years. Thus no sustainable development can be attained in eastern Africa without effective mainstreaming of climate information in the development policies, plans and programmes. Many past studies in the region have focused on rainfall variability at seasonal, annual and decadal scales. Very little work has been done at intraseasonal timescale that is paramount to most agricultural applications. This study aims at filling this research gap, by investigating the structure of rainfall season in terms of the distribution of wet and dry spells and how this distribution varies in space and time at interannual time scale over Equatorial Eastern Africa. Prediction models for use in the early warning systems aimed at climate risk reduction were finally developed. The specific objectives of the study include, delineate and diagnose the some aspects of the distribution of the wet and dry spells at interannual timescale; investigate the linkages between the aspects of the distribution of wet and dry spells identified and dominant large scale climate fields that drive the global climate; and assess the predictability of the various aspects of wet and dry spells for the improvement of the use in the early warning systems of the region.Several datasets spanning a period of 40 years (1961 - 2000) were used. The data included gauged daily rainfall amount for the three Eastern Africa countries namely Kenya, Uganda, and Tanzania; Hadley Centre Sea Surface Temperature (SST); re-analysis data and radiosonde observations from Nairobi (Kenya) and Bangui (Central Africa Republic) upper air stations. The indices of El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole and SST gradients which constituted the predefined predictors were also used [...]
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Makkawi, Yassir T. Makkawi. "Investigation of dry and semi-wet fluidized bed hydrodynamics utilizing twin-plane electrical capacitance tomography." Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/360.
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Thoithi, Wanjiru. "Assessing dry spell and wet day frequencies over southern Africa during the summer rainy season." Master's thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33990.
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Rainfall over southern Africa experiences substantial temporal and spatial variability which heavily impacts poor rural populations in the region that rely on rainfed agriculture for their livelihoods. Instead of totals, seasonal rainfall is better characterised by wet and dry events occurring within rainy seasons as knowledge of the frequency of such events is able to inform agricultural activity. Dry spells (pentads having <5 mm) and moderate wet days (10-30 mm) over southern Africa were assessed using high resolution (0.05◦) Climate Hazards group Infrared Precipitation with Stations (CHIRPS) datasets over the period 1981/82-2018/19 during October-November (ON), December-February (DJF) and March-April (MA) using climatology, intensity-frequency and trend analysis. Correlations with SST over the tropical southeast Atlantic and climate modes namely, El Nino Southern Oscillation (ENSO), the Subtropical ˜Indian Ocean Dipole (SIOD) and Southern Annular Mode (SAM) were computed. These, together with regressed atmospheric and SST fields were used to identify possible mechanisms for changes in dry spell and moderate wet day frequencies during austral summer. Two strong gradients in dry spell frequency were found to be present during DJF, one diagonal along the western margins of the Kalahari desert and the other meridional, lying across 20-24◦S. Topographic influences on rainfall were observed near the Drakensberg and Chimanimani mountains, Mulanje massif and Madagascan highlands where dry spell frequency (DSF) (moderate wet day frequency (MWDF)) tended to be relatively lower (higher). A region which frequently experienced half of the season as dry was identified lying across 22-24◦S (18-25◦S) during DJF (MA), with a core in the central Limpopo River Valley where 85-100% (100%) of the seasons were dry for half the season. DSF and MWDF trends indicated that drying has occurred over central South Africa during ON whereas decreasing DSF and increasing MWDF trends pointed to a weakening diagonal and meridional gradient during DJF. Additionally, increasing MWDF trends over important agricultural areas have occurred during DJF. Trends over central South Africa, part of the diagonal gradient, were associated with changes in ENSO, SAM, the Botswana High and SST in the SE Atlantic whereas those in the western Botswana region, part of the meridional gradient, were associated with those in the SIOD, Mozambique Channel Trough and Mascarene High and SST in the eastern and western Pacific.
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Alsaiari, Abdulmohsen Omar. "Augmentation of Jet Impingement Heat Transfer on a Grooved Surface Under Wet and Dry Conditions." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/98502.
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Array jet impingement cooling experiments were performed on flat and grooved surfaces with the surface at a constant temperature. For the flat surface, power and temperature measurements were performed to obtain convection coefficients under a wide range of operating conditions such as jet speed, orifice to surface stand-of distance, and open area percentage. Cooling performance (CP) was calculated as the ratio between heat transfer and fan power. An empirical model was developed to predict jet impingement heat transfer taking into account the entrainment effects. Experimental results showed that jet impingement can provide high transfer rates with lower rates of cooling cost in comparison to contemporary conventional techniques in the industry. CP values over 279 were measured which are significantly higher than the standard values of 70 to 95 in current technology. The model enhanced prediction accuracy by taking into account the entrainment effects; an effect that is rarely considered in the literature. Experiments on the grooved surfaces were performed at dry and wet surface conditions. Under dry conditions, results showed 10%~55% improvement in heat transfer when compared to the flat surface. Improvement percentage tends to be higher at wider gaps between the array of orifices and the grooved surface. An improvement of 30%~40% was observed when increasing Re either by increasing orifice diameter or jet speed. Similar improvement was observed at higher flow open area percentages. No significant improvement in heat transfer resulted from decreasing the size of the grooves from 3.56mm to 2.54mm. Similarly, no noticeable change in heat transfer resulted from changing the relative position of the jets striking the surface at the top of the grooves to the bottom of the grooves. Deeper grooves with twice the depth gave statistically similar average heat transfer coefficients as shallower grooves. Under wet conditions, a hybrid cooling technique approach was proposed by using air jets impinging on a grooved surface with the grooves containing water. The approached is proposed and evaluated experimentally for its feasibility as an alternative for cooling towers of thermoelectric power plants. Convection heat and mass transfer coefficients were measured experimentally using the heat mass transfer analogy. Results showed that hybrid jet impingement provided high magnitudes of heat flux at low jet speeds and flow rates. High coefficients of performance CP > 3000, and heat fluxes > 8,000W/m2 were observed. Hybrid jet impingement showed 500% improvement as compared to jet impingement on a dry flat surface. CP values of hybrid jet impingement is 600% to 1,500% more as compared to performance of air-cooled condensers and wet cooling towers. Water use for hybrid jet impingement cooling is efficient since evaporation energy is absorbed from the surface directly instead of cooling air to near wet-bulb temperature.PHD
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Portugal, André Fernandes Vaz. "Validation of a FEM-based tool and implementation of tyres' dry and wet braking prediction." Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/22755.
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Mestrado em Engenharia MecânicaIn the present document, a new explicit FEM-based software developed to optimize tyre pattern geometry is presented. The new software calculates forces and displacements in tyre tread components after applying a load and a longitudinal shear displacement. To overcome long meshing and calculation times, simplifications are made. In this work, the usability of the simplifications is checked and the new software is adjusted and validated through the use of other FEM-based software in the market (Abaqus). To perform the validation, models are created, reproducing tyre tread blocks with different geometries, and the same simulation is reproduced in Abaqus. A set of simulations is run in both software. The results of the simulations are compared regarding the final shape, reaction forces and displacements in the nodes of the models. Finally, simple friction formulations are proposed and implemented in the new software, as well as a slip parameter and a water height level in the tyre footprint, in order to simulate braking performance in dry and wet surfaces. The results are then compared with experimental tests.
No presente documento, um novo software baseado no Método dos Elementos Finitos (MEF) explícito, desenvolvido para otimizar a geometria do padrão de pneus é apresentado. O novo software calcula forças e deslocamentos em componentes do piso dos pneus após a aplicação de uma carga e um deslocamento longitudinal. Para superar longos tempos de geração de malha e de cálculo, simplificações são feitas. Neste trabalho, a viabilidade para a utilização das simplificações é verificada e o novo software é ajustado e validado através da utilização de outro software baseado no MEF no mercado (Abaqus). Para executar a validação, modelos são criados, reproduzindo blocos do piso do pneu com diferentes geometrias, e a mesma simulação é reproduzida no Abaqus. Um conjunto de simulações é executado em ambos os softwares. Os resultados das simulações são comparados em relação à forma final, às forças de reação e deslocamentos nos nós dos modelos. Finalmente, simples formulações de fricção são propostas e implementadas no novo software, bem como um parametro de deslizamento e nível da altura da camada de água na pegada do pneu, a fim de simular o desempenho de travagem em piso seco e molhado. Os resultados são, então, comparados com testes experimentais.
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Kayahan, Ahmet. "Compressibility Of Various Coarse-grained Fill Materials In Dry And Wet Loading Conditions In Oedometer Test." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1052539/index.pdf.
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The use of coarse-grained fill materials has grown significantly in recent years especially on account of their use in dams and transportation networks. This study investigates compressibility of various coarse-grained fill materials in dry and wet loading conditions in oedometer test. Four materials were used in the experiments, which falls into GP, GW, GM and GC categories respectively. GP material is a weathered rock obtained from Eymir Lake region. This material was chosen especially to be able to investigate degradation and particle breakage due to compaction and compression. GW, GM and GC materials were obtained by using the material called &lsquobypass&rsquo
which is a fill material used in the construction of metro of Eryaman. Using these four materials, large-scale double oedometer tests were carried out to investigate compressibility in both dry and wet conditions. The double oedometer testing technique is used to investigate the effect of soaking on compressibility behaviour of compacted fill materials. Various compactive efforts were used in the compaction stage to investigate the effect of compactive effort on compressibility and degradation of the four gravelly materials. Gradations of the post-test samples were obtained and particle breakage due to compaction using various compactive efforts and particle breakage due to compression were determined. It is found that amount of compression does not necessarily depend on the dry density of the material and fine fraction is also a dominating property regarding the compressibility in coarse-grained fill materials. The vertical strains induced by soaking are on the order of 12% - 20% of the compression measured in dry loading case for the well-graded coarse-grained fill materials tested. Besides, there is significant particle breakage in the compaction process and no further particle breakage in the oedometer test for GP material.
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Li, Chaoran [Verfasser], and J. [Akademischer Betreuer] Winter. "Wet and Dry Anaerobic Digestion of Biowaste and of Co-substrates / Chaoran Li. Betreuer: J. Winter." Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/1068263415/34.
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Bostwick, LAURA. "Laboratory study of geosynthetic clay liner shrinkage when subjected to wet/dry cycles." Thesis, 2009. http://hdl.handle.net/1974/1919.
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Geosynthetic Clay Liners (or GCLs) are often used in conjunction with a geomembrane for landfills and heap-leach pads, where their function is to minimize leakage that may occur through holes in the geomembrane. GCLs are installed with overlapping panels and powdered bentonite placed between the overlaps to provide a better seal.
Recent field exhumations of GCLs installed beneath a geomembrane left exposed to solar radiation have shown panel shrinkage; in some cases, this shrinkage was enough to leave exposed areas unprotected by the GCL. One hypothesized cause of this shrinkage is cyclic wetting and drying of the GCL.
To investigate the hypothesis that wet/dry cycles have the potential to cause irrevocable shrinkage of GCL panels, a total of 8 different products were tested under idealised conditions in the laboratory. Shrinkage was measured using both hand measurements and digital image correlation techniques. A number of variables were tested for their effects on panel shrinkage, including mass per unit area, size and aspect ratio, restraint, moisture content and wetting conditions, and GCL type. Wet/dry cycles were found to cause sufficient shrinkage to explain the shrinkage observed in all but one field case. The shrinkage of any particular product was found to be variable. In particular the shrinkage was found to be sensitive to the distribution of the mass of bentonite within a specimen with the highest shrinkage being observed when there was the greatest variability in mass distribution. It is shown that some GCL products are more prone to shrinkage than others.
Consideration is also given to the potential effectiveness of heat-tacking of GCL seams to reduce panel shrinkage in the field. Specimens of GCL which had been heat-tacked in the field were tested under similar cyclic conditions as used in the abovementioned laboratory tests, and the shrinkage response noted. The results indicate that such a technique has promise as a method of inhibiting shrinkage of the two products found to exhibit loss of panel overlap in published field situations. However, more work is required to confirm that this does not create other problems.Thesis (Master, Civil Engineering) -- Queen's University, 2009-05-31 22:58:36.59
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Swanepoel, Wayne. "Wet compression versus dry compression in refrigeration cycles working with pure or non-azeotropic refrigerant mixtures for air-conditioners." Thesis, 2012. http://hdl.handle.net/10210/6097.
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M.Ing.Wet compression versus dry compression in refrigeration cycles working with pure refrigerants or non-azeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants and refrigerant mixtures were analysed for one cooling application, namely that of spatial air conditioning at an evaporating temperature of 7°C, and a condensing temperature of 50°C. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better cooling COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves consistently produce higher cooling COP's when wet compression is used. However, their cooling capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the exceptions that do exist, some manage to produce relatively high COP c 's while retaining competitive cooling capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.
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Su, Ken Yu Jen. "Effect of Laser Welding and Stretch Forming on the Corrosion Performance of Hot-Dip Galvanized Steel." Thesis, 2008. http://hdl.handle.net/10012/4088.
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The use of laser welding in the automotive industry in the past few decades has facilitated joining of hot-dip galvanized (HDG) steel sheets at high production rates and low cost. The recent development of tailor welded blanks (TWB) using laser welding allowed combinations of sheet grades and thicknesses to “tailor” the vehicle part for optimized design, structural integrity and crash performance but more importantly, reductions in weight. Welded blanks are further subjected to stamping or stretch forming prior to final assembly. Unfortunately, both welding and stretch forming cause the galvanized coating to deteriorate, and thereby, undermine the long term corrosion protection. Despite existing publications on zinc coated steel and advances in processing techniques, there is a lack of understanding on the influence of laser welding and stretch forming on the corrosion performance of HDG steel. Hence, the purpose of this study was to determine how welding speed and biaxial strain affect interstitial-free (IF) and high strength low allow (HSLA) steel coupons when they are subjected to continuous immersion and accelerated corrosion tests. The corrosion rates of the coupons were evaluated using electrochemical techniques and gravimetry.
Changes in the galvanized coating were characterized using scanning electron metallography. It was observed that, the original zinc layer transformed into the delta and gamma Fe-Zn intermetallic phases locally in the heat affected zone (HAZ) after laser welding. The resulting microstructure was similar to that of a commercially galvannealed coating and exhibited superior corrosion resistance than that of pure zinc.
Linear polarization resistance (LPR) measurements revealed that the zinc coating was able to protect a chemically exposed region of steel in 0.1 M NaCl solution. While the Nd:YAG laser welded coupons with narrow HAZs performed equally well as the non-welded ones, diode laser welded coupons, with a wide locally annealed coating in the HAZ, exhibited a decrease in the peak corrosion rate of zinc. Moreover, minimal amounts of rust were observed on the surface of the HAZ after testing. With biaxial strain, welded and deformed coupons generally demonstrated higher peak corrosion rates than that of undeformed welded ones.
When subjected to cyclic corrosion testing according to SAE J2334, rust formed in the exposed region after one 24 hour test cycle due to wet-dry conditions. However, zinc corrosion products on the surface provided substantial corrosion resistance to the remaining zinc coating and to the steel substrate. Gravimetric measurements of welded coupons showed a linear increase in weight gain with increased exposed widths of the steel after 30 cycles but biaxial strain further increased the weight gain on deformed coupons. After 60 cycles, the trend became exponential for both welded and deformed coupons. There was a negligible difference between the corrosion performance of IF and HSLA steel.
Using X-Ray diffraction and Raman spectroscopy, species of both iron and zinc corrosion products were identified. Without the application of paint coatings, zinc oxide (ZnO), zinc hydroxy chloride (ZnCl2[Zn(OH)2]4), and hydrozincite ([ZnCO3]2[Zn(OH)2]3) were responsible for passivating the surface and reducing the overall corrosion rate of the galvanized coating.
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Cheng, Fu-Pen, and 鄭福本. "The cyclic oxidation behavior of welded Ni-base superalloys at 950oC in dry and wet air." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/39852041160380415341.
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碩士國立臺灣海洋大學
材料工程研究所
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The cyclic oxidation behavior of three Ni-based¬-superalloy welds containing Hastelloy X (X), Incoloy 800H (800H), and Inconel 617 (617), in which each alloy contained the original substrate (M-SUB, where M could be X, 800H, or 617), the heat-affected zone (M-HAZ) and the melting zone (M-MZ) was studied at 950oC in dry/wet air. The results indicated that the oxidation kinetics of all the alloys in dry air followed a parabolic-rate law, indicating that diffusion is the rate-controlling step. In general, the steady-state oxidation rates of the M-HAZ regions are always faster than those of the M-SUB regions, while those of M-MZ regions may change dramatically, strongly depending on the filler. Based on the oxidation kinetics studied, the oxidation rate constants (kp values) of 800H-MZ are slower than those of 800H-SUB, while those of X-MZ are faster than those of X-SUB. Nearly no kinetics difference is obtained for both 617-MZ and 617-SUB. The oxidation kinetics of the alloys in wet air initially revealed a mass-gain stage, while a significant mass-lose stage was observed for a prolong exposure. The 800H-SUB and 800H-HAZ revealed the fast oxidation rates among the alloys studied. Duplex scales always formed on all the alloys in dry air, consisting of an outer-layer of mixture Cr2O3 and MCr2O4 (M=Fe, Mn, or Ni) and an exclusive inner-layer of Cr2O3. In addition, the internal-oxidation precipitates were always observed just beneath the scale/substrate interface. The scales formed in wet air are similar to those in dry air, except for that the more porous scale structure was noted.
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Westfall, Erin. "Wet/Dry Mapping - 2008 Wet/Dry Poster." 2008. http://hdl.handle.net/10150/146073.
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