Dissertations / Theses on the topic 'WATER PRESSURE HEAD'

Previous studies of agricultural conditions in the Mekong Delta (MD) have identified soil compaction as an obstacle to sustainable production. A conceptual model for soil formation was presented to demonstrate the link between soil hydrology and plant response. Detailed studies of soil moisture dynamics in agricultural fields were conducted using a dynamic process-orientated model. Pressure head and water flow were simulated for three selected sites during a year for which empirical data were available. Daily meteorological data were used as dynamic input and measured pressure head was used to estimate parameter values that satisfied various acceptance criteria. The Generalised Likelihood Uncertainty Estimation (GLUE) approach was applied for calibration procedures with 10,000 runs, each run using random values within the chosen range of parameter values. To evaluate model performance and uncertainty estimation, re-sampling was carried out using coefficient of determination (R2) and mean error (ME) as the criteria. Correlations between parameters and R2 (and ME) and among parameters were also considered to analyse the relationship of the selected parameter set in response to increases/decreases in the acceptable simulations. The method was successful for two of the three sites, with many accepted simulations. For these sites, the uncertainty was reduced and it was possible to quantify the importance of the different parameters.

 

The aim of this work is to study the relation between two invariants of water flow in a channel of finite depth. The first invariant is the height of the water wave and the second one is the flow force. We restrict ourselves to water waves of small amplitude. Using asymptotic technique together with the method of separation of variables, we construct all water waves of small amplitude which are parameterized by a small parameter. Then we demonstrate numerically that the flow force depends monotonically on the height.

Spray cooling is a high heat removal technique which has been used widely in many industries, especially metallurgical, where the control of the temperatures of metals is an important factor to obtain the desired microstructure; and also in microelectronics where is very important to obtain high heat fluxes at relatively low surface temperatures. In this study, an open loop spray cooling system has been fabricated to provide an upward-facing spray over a 12 mm diameter test surface. A full cone spray nozzle was used to deliver deionized water to the test surface at five pressures (10, 15, 20, 25 and 30 psi), and at three different distances to the test surface (3, 7 and 12 mm). The volumetric flow rate at the surface used in the experiments depended on both the pressures and the distances. For a distance of 3 mm and 7 mm, the volumetric flow rate range from 336.6 to 627 ml/min while for 12 mm, the range was from 336.6 to 484.28 ml/min. Heat fluxes of 1.92 to 451 W/cm2, 2.1 to 417.3 W/cm2 and 1.9 to 409.5 W/cm2 for distances of 3, 7 and 12 mm respectively were registered at different input power levels. For all the three distances, the volumetric flow rate affects the heat flux, especially for 3 mm; and this effect decreases for higher distances. However, the distance between the nozzle and the test surface has little effect on the heat flux at low pressures but at higher pressures, the difference in heat flux is mainly due to the fact that part of the spray does not impinge the test surface.

In this thesis I review the sufficient flow capacity of the safety valve against high-pressure heater thermal pressurization in high-pressure feedwater heater on nuclear power Dukovany. I present basic possible cases of thermal pressurization both a high node heater, and the extended pressure unit in case of closure all power heads to steam generators.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 285-290).
A nanofluid is a colloidal suspension of nano-scale particles in water, or other base fluids. Previous pool boiling studies have shown that nanofluids can improve the critical heat flux (CHF) by as much as 200%. In this study, subcooled flow boiling heat transfer and CHF experiments were performed with low concentrations of alumina, zinc oxide, and diamond nanoparticles in water (< 0.1 % by volume) at atmospheric pressure. It was found that for comparable test conditions the values of the nanofluid and water heat transfer coefficient (HTC) are similar (within ±20%). The HTC increased with mass flux and heat flux for water and nanofluids alike, as expected in flow boiling. The CHF tests were conducted at 0.1 MPa and at three different mass fluxes (1500, 2000, 2500 kg/m2s) under subcooled conditions. The maximum CHF enhancement was 53%, 53% and 38% for alumina, zinc oxide and diamond, respectively, always obtained at the highest mass flux. The measurement uncertainty of the CHF was less than 6.2%. A post-mortem analysis of the boiling surface reveals that its morphology is altered by deposition of the particles during nanofluids boiling. A confocal-microscopy-based examination of the test section revealed nanoparticles deposition not only changes the number of micro-cavities on the surface, but also the surface wettability. A simple model was used to estimate the ensuing nucleation site density changes, but no definitive correlation between the nucleation site density and the heat transfer coefficient data could be found.
(cont.) Wettability of the surface was substantially increased for heater coupons boiled in alumina and zinc oxide nanofluids, and such wettability increase seems to correlate reasonably well with the observed marked CHF enhancement for the respective nanofluids. Interpretation of the experimental data was conducted in light of the governing surface parameters and existing models. It was found that no single parameter could explain the observed HTC or CHF phenomena. The existing models were limited in studying the surface effects, suggesting that more accurate models incorporating surface effects need to be developed. Finally, the research activities performed in this thesis help identify the research gaps and indicate future research directions.
by Sung Joon Kim.
Ph.D.

The detection of trace explosives in the subsurface is an active area of research for landmine detection. Understanding the air-water flow and heat transport phenomena in the subsurface plays an important role in improving chemical vapor detection. Implementing a finite element method that accurately captures water vapor transport in the vadose zone is still an open question. A non-equilibrium, pressure-pressure formulation has been implemented based on Smits, et al [22]. This implementation consists of four equations: a wetting phase (water) mass balance equation, a non-wetting phase (air) mass balance equation, a water vapor transport equation, and a heat transport equation. This work will compare two implementations, a fully coupled approach and an operator splitting approach for the water vapor and heat transport equations. The formulation of the methods will be presented and the methods will be tested using collected data from physical experiments.

The current study is part of a long term experimental project devoted to investigating single-phase flow pressure drop and heat transfer, flow boiling pressure drop and heat transfer, flow boiling instability and flow visualization of de-ionized water flow in microchannels. The experimental facility was first designed and constructed by S. Gedupudi (2009) and in the present study; the experimental facility was upgraded by changing the piping and pre-heaters so as to accommodate the objectives of the research. These objectives include (i) modifying the test rig, to be used for conducting experiments in microchannels in single and two-phase flow boiling heat transfer, pressure drop and visualization, (ii) redesign metallic single microchannels using copper as the material. The purpose of the redesign is to provide microchannels with strong heaters, high insulation performance and with test sections easy to dismantle and reassemble, (iii) obtaining the effect of hydraulic diameter on single-phase flow, flow pattern, heat transfer and pressure drop, (iv) studying the effects of heat flux, mass flux,and vapour quality on flow pattern, flow boiling heat transfer and pressure drop, (v)comparing experimental results with existing correlations. However, the main focus in this present study is to investigate the effects of hydraulic diameter, heat flux, mass flux and vapour quality on flow pattern, flow boiling heat transfer coefficient and pressure drop. In addressing (iii) many possible reasons exist for the discrepancies between published results and conventional theory and for the scatter of data in published flow boiling heat transfer results: 1. Accuracy in measuring the dimensions of the test section, namely the width, depth and length and in the tested variables of temperature, pressure, heat flux and mass flux. 2. Variations in hydraulic diameter and geometry between different studies. 3. Differences in working fluids. 4. Effects of hydrodynamic and thermal flow development 5. Inner surface characteristics of the channels. Three different hydraulic diameters of copper microchannels were investigated: 0.438mm, 0.561 mm and 0.635 mm. For single-phase flow the experimental conditions included mass fluxes ranging from 278 – 5163 kg/m2 s, heat fluxes from 0 - 537 kW/m², and inlet temperatures of 30, 60 and 90°C. In the flow boiling experiments the conditions comprised of an inlet pressure of 125 kPa (abs), inlet temperature of 98°C (inlet sub-cooling of 7 K), mass fluxes ranging from 200 to 1100 kg/m²s, heat fluxes ranging from 0 to 793 kW/m² and qualities up to 0.41. All measurements were recorded after the system attained steady states. The single-phase fluid flow results showed that no deviation of friction factors was found from the three different hydraulic diameters. The effect of fluid temperature on friction factor was insignificant and the friction factors themselves were in reasonable agreement with developing flow theory. The typical flow patterns observed in all three test sections were bubbly, slug/confined churn and annular, however, based on the observation performed near the outlet, the bubbly flow was not detected. The effects of mass flow and hydraulic diameter on flow pattern for the three test sections investigated in the range of experimental conditions were not clear. The single-phase heat transfer results demonstrated that smaller test sections result in higher heat transfer coefficients. However, for heat transfer trends presented in the form of Nusselt number versus Reynolds number, the effect of hydraulic diameter was insignificant.The flow boiling experiments gave similar heat transfer results; they exhibited that the smaller hydraulic diameter channels resulted in higher heat transfer coefficients. The nucleate boiling mechanism was found for all three test sections, evidenced by the significant effect of heat flux on the local heat transfer coefficient. Moreover, the heat flux had a clear effect on average heat transfer coefficient for the 0.561 mm and 0.635mm test sections, whilst for the 0.438 mm test section, there was no discernible effect. At the same heat flux, increases in mass flux caused heat transfer coefficients to decrease. This could be due to the decrease of pressure inside the test section. When a higher mass flux was tested, the inlet pressure increased, and in reducing the inlet pressure to the original value, a decrease in system pressure resulted. Consequently, the outlet pressure and local pressure became lower. Existing flow pattern maps, flow boiling heat transfer and pressure drop correlations were compared with the experimental results obtained for all three test sections. The comparison showed that the flow pattern map proposed by Sobierska et al. (2006) was the most successful in predicting the experimental data. The local heat transfer coefficient data were compared with existing published correlations. The correlations of Yu et al. (2002), Qu and Mudawar (2003) and Li and Wu (2010) are found to predict the current local heat transfer coefficient better than other correlations tested. Pressure drop results showed that as the heat flux and mass flux were increased, the two-phase pressure drop increased too. These were due to the increase in bubble generations and the inertia momentum effect. As the channel was reduced, the twophase pressure drop increased because the pressure drop related inversely with the channel hydraulic diameter. The pressure and pressure drop fluctuations were indentified in this project, however, the maximum pressure fluctuation was found in the 0.438 mm channel whilst the minimum fluctuation was attained in the 0.561 mm channel. This indicated that the effect of decreasing in hydraulic diameter on pressure and pressure drop fluctuations is not clear and needs to be investigated further. The two-phase pressure drop data were compared with selected correlations. The Mishima and Hibiki (1996)’s correlation was found to predict the current two-phase pressure drop better than the other correlations examined in this study.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2008.
"January 2007."
Includes bibliographical references (leaves 69-70).
The objective of this study is to evaluate experimentally the convective heat transfer and viscous pressure loss characteristics of alumina-water and zirconia-water nanofluids. Nanofluids are colloidal dispersions of nanoparticles in metal, metal oxide, carbon-based materials in base fluids, and may offer improved heat transfer properties compared with pure base fluids. A flow loop with a vertical heated section was designed and constructed to operate in the laminar flow regime (Re<2000). Initial tests were conducted with deionized water for experiment validation. Alumina nanofluid was tested in the flow loop at four different volumetric loadings, 0.6%, 1%, 3% and 6% and zirconia nanofluid was tested at volumetric loadings of 0.3%, 0.64% and 1.3%. The experimental results, represented in Nusselt number (Nu) and dimensionless length x+, are in good agreement with traditional model predictions if the loading- and temperature- dependent thermophysical properties are utilized. Measured pressure loss of the nanofluid is within 20% of theory. It is concluded that the laminar convective heat transfer and viscous pressure loss behavior of alumina-water and zirconia-water nanofluids can be predicted by existing models as long as the correct mixture properties are used, and there is no abnormal heat transfer enhancement.
by Ulzie L. Rea.
S.B.

Target of the master´ thesis is a design of heat exchanger air-water with the air flowing inside the pipes and with staggered pipe configuration, based on the engaged and chosen values. Next target is to determine heat exchanger with cross parallel flow and cross countercurrent flow of mediums, pressure drop on both sides air and water and dimensions of intake and outgoing gate on both sides air and water.

Land application of wastes has become increasingly popular, to promote nutrient recycling and environmental protection, with soil functioning as a partial barrier between wastes and groundwater. Dairy shed effluent (DSE), may contain a wide variety of pathogenic micro-organisms, including bacteria (e.g. Salmonella paratyphyi, Escherichia coli. and Campylobacter), protozoa and viruses. Groundwater pathogen contamination resulting from land-applied DSE is drawing more attention with the intensified development of the dairy farm industry in New Zealand. The purpose of this research was to investigate the fate and transport of bacterial indicator-faecal coliform (FC) from land-applied DSE under different irrigation practices via field lysimeter studies, using two water irrigation methods (flood and sprinkler) with contrasting application rates, through the 2005-2006 irrigation season. It was aimed at better understanding, quantifying and modelling of the processes that govern the removal of microbes in intact soil columns, bridging the gap between previous theoretical research and general farm practices, specifically for Templeton soil. This study involved different approaches (leaching experiments, infiltrometer measurements and a dye infiltration study) to understand the processes of transient water flow and bacterial transport; and to extrapolate the relationships between bacterial transport and soil properties (like soil structure, texture), and soil physical status (soil water potential ψ and volumetric water content θ). Factors controlling FC transport are discussed. A contaminant transport model, HYDRUS-1D, was applied to simulate microbial transport through soil on the basis of measured datasets. This study was carried out at Lincoln University’s Centre for Soil and Environmental Quality (CSEQ) lysimeter site. Six lysimeters were employed in two trials. Each trial involved application of DSE, followed by a water irrigation sequence applied in a flux-controlled method. The soil columns were taken from the site of the new Lincoln University Dairy Farm, Lincoln, Canterbury. The soil type is Templeton fine sandy loam (Udic-Ustochrept, coarse loamy, mixed, mesic). Vertical profiles (at four depths) of θ and ψ were measured during leaching experiments. The leaching experiments directly measured concentrations of chemical tracer (Br⁻ or Cl⁻) and FC in drainage. Results showed that bacteria could readily penetrate through 700 mm deep soil columns, when facilitated by water flow. In the first (summer) trial, FC in leachate as high as 1.4×10⁶ cfu 100 mL⁻¹ (similar to the DSE concentration), was detected in one lysimeter that had a higher clay content in the topsoil, immediately after DSE application, and before any water irrigation. This indicates that DSE flowed through preferential flow paths without significant treatment or reduction in concentrations. The highest post-irrigation concentration was 3.4×10³ cfu 100 mL⁻¹ under flood irrigation. Flood irrigation resulted in more bacteria and Br⁻ leaching than spray irrigation. In both trials (summer and autumn) results showed significant differences between irrigation treatments in lysimeters sharing similar drainage class (moderate or moderately rapid). Leaching bacterial concentration was positively correlated with both θ and ψ, and sometimes drainage rate. Greater bacterial leaching was found in the one lysimeter with rapid whole-column effective hydraulic conductivity, Keff, for both flood and spray treatments. Occasionally, the effect of Keff on water movement and bacterial transport overrode the effect of irrigation. The ‘seasonal condition’ of the soil (including variation in initial water content) also influenced bacterial leaching, with less risk of leaching in autumn than in summer. A tension infiltrometer experiment measured hydraulic conductivity of the lysimeters at zero and 40 mm suction. The results showed in most cases a significant correlation between the proportion of bacteria leached and the flow contribution of the macropores. The higher the Ksat, the greater the amount of drainage and bacterial leaching obtained. This research also found that this technique may exclude the activity of some continuous macropores (e.g., cracks) due to the difference of initial wetness which could substantially change the conductivity and result in more serious bacterial leaching in this Templeton soil. A dye infiltration study showed there was great variability in water flow patterns, and most of the flow reaching deeper than 50 cm resulted from macropores, mainly visible cracks. The transient water flow and transport of tracer (Br⁻) and FC were modelled using the HYDRUS-1D software package. The uniform flow van Genuchten model, and the dual-porosity model were used for water flow and the mobile-immobile (MIM) model was used for tracer and FC transport. The hydraulic and solute parameters were optimized during simulation, on the basis of measured datasets from the leaching experiments. There was evidence supporting the presence of macropores, based on the water flow in the post-DSE application stage. The optimised saturated water content (θs) decreased during the post-application process, which could be explained in terms of macropore flow enhanced by irrigation. Moreover, bacterial simulation showed discrepancies in all cases of uniform flow simulations at the very initial stage, indicating that non-equilibrium processes were dominant during those short periods, and suggesting that there were strong dynamic processes involving structure change and subsequently flow paths. It is recommended that management strategies to reduce FC contamination following application of DSE in these soils must aim to decrease preferential flow by adjusting irrigation schemes. Attention needs to be given to a) decreasing irrigation rates at the beginning of each irrigation; b) increasing the number of irrigations, by reducing at the same time the amount of water applied and the irrigation rate at each irrigation; c) applying spray irrigation rather than flood irrigation.

This thesis describes the development and validation of a look-up table capable of predicting heat transfer to water flowing vertically upward in a circular tube in the trans-critical pressure range from 19 to 30 MPa. The table was based on an extensive and screened experimental database and its trends were smoothened to remove unrealistic scatter and physically implausible discontinuities. When compared to other prediction methods, the present look-up table approximated the experimental data closer in values and trends. Moreover, unlike existing prediction methods, the table applies not only to normal heat transfer conditions but also to conditions with heat transfer deterioration and enhancement. A separate multi-fluid look-up table for trans-critical heat transfer was also developed, which besides the existing water database incorporated new measurements in carbon dioxide; the latter were collected at the University of Ottawa supercritical flow loop under conditions of interest for the current Super-Critical Water-Cooled Reactor designs, for which few water data were available in the literature. Existing fluid-to-fluid scaling laws were tested and two additional sets of scaling laws were proposed, which are applicable not only to the supercritical pressure region, but also to the high pressure subcritical region. The multi-fluid table is applicable to water at conditions of normal and abnormal heat transfer, but its applicability to model fluids is restricted to the normal heat transfer mode.

This experimental research aims at investigating the single-phase flow heat transfer and friction factor, flow boiling heat transfer and pressure drop, and flow visualisation in microchannels using de-ionized water. In the literature, many studies failed to explain the effect of aspect ratio on the single-phase and two-phase flow heat transfer rate and pressure drop. Because the channel aspect ratios and hydraulic diameters were varied together in those studies. Also, there is a discrepancy between past studies and the conventional theory for the flow boiling heat transfer characteristics. Accordingly, the objectives of this research can be listed as follows: (i) modifying the existing experimental facility to perform single-phase and two-phase flow heat transfer and pressure drop and two-phase flow pattern visualization experiments in microchannels, (ii) clarifying the fundamental aspects of flow boiling in micro passages, (iii) investigating the aspect ratio, heat flux, mass flux and vapour quality effects on flow patterns, heat transfer rate and pressure drop in single-phase and two-phase flow, (iv) comparing the obtained results with heat transfer and pressure drop correlations and flow pattern maps available in the literature. Consequently, the pre-existing experimental facility was modified in the current research by changing the pre-heaters, flowmeter and piping in order to achieve the goals of this study. Four copper rectangular microchannels were designed and manufactured. Three microchannel test sections having the same hydraulic diameter and length but different aspect ratios were investigated to reveal the effect of aspect ratio on the single-phase and two-phase flow heat transfer rate and pressure drop. The surface roughness of each microchannel was also examined. It was found that the surface roughnesses of all microchannels are similar. Moreover, an additional microchannel test section was used to examine the effect of heated length on the flow boiling heat transfer coefficient and pressure drop. The single-phase flow results demonstrated that the channel aspect ratio has no influence on the friction factor and heat transfer rate for the tested microchannels and experimental range. In the flow boiling experiments, bubbly, bubbly/slug, slug, churn and annular flow regimes were observed in the tested microchannels. The channel aspect ratio effect was found to be small on the observed flow patterns. The experimental flow patterns were predicted well by the flow pattern map proposed by Galvis and Culham (2012) except for the slug flow regime. The flow pattern maps of Sobierska et al. (2006) and Harirchian and Garimella (2009) reasonably predicted the experimental flow pattern data. The flow boiling heat transfer results showed that the prevailing heat transfer mechanism is nucleate boiling for the low and medium heat flux inputs. On the other hand, the dominant heat transfer mechanism is unclear at the high heat flux inputs while smaller aspect ratio microchannel has better heat transfer performance for low and medium heat flux inputs. However, at high heat flux inputs the channel aspect ratio effect was found to be insignificant on the flow boiling heat transfer coefficient. The experimental flow boiling heat transfer coefficient data were reasonably predicted by the correlations of Sun and Mishima (2009), Li and Wu (2010) and Mahmoud and Karayiannis (2011) from the literature. The flow boiling pressure drop characteristics were also examined in the tested microchannels. Outcome of the experiments consistently indicated a highly linear trend between the increasing flow boiling pressure drop and the heat and mass flux. Also, the flow boiling pressure drop increased with the increase in vapour quality. The effect of channel aspect ratio on the flow boiling pressure drop was also assessed. It was found that when the channel aspect ratio decreased, the flow boiling pressure drop increased. The experimental flow boiling pressure drop data were compared to correlations from the literature. Mishima and Hibiki (1996), Yu et al. (2002) and Zhang et al. (2010) correlations reasonably predicted the experimental flow boiling pressure drop results.

The subject of the presented thesis is a foundation pit dewatering numerical analysis. The study is introduced with practical examples and the summary of the necessary theory. Individual subtasks are modeled as two or three-dimensional problem on a chosen foundation pit example. A comparison with analytical methods and theoretical knowledge about the problem is made. The studies focus on specifying the pumped water quantity, the shape of the depression curve, determining the size of the numerical model and the influence of the finite element network density. The steady-state flow cases, water table aquifer, a well system, sheet pile wall cutoff effect, surface drained pit and partial penetration cases are analyzed. The work proposes a method of modeling a well by FEM. The main output is a 3D analysis of a submerged excavation dewatered with a partially penetrated well system.

Lors d’une insertion accidentelle de réactivité dans un réacteur nucléaire expérimental, la puissance du cœur peut augmenter de manière exponentielle, avec un temps caractéristique allant de quelques millisecondes à quelques centaines de millisecondes. À cause des effets neutroniques et thermohydrauliques, le système peut atteindre les conditions de crise d’ébullition à même d’engendrer une réaction explosive. Bien que la crise d’ébullition ait été largement étudiée en conditions de chauffage stationnaires, ce n’est pas le cas pour les transitoires notamment de type excursions de puissance. Le but de ce travail est donc de comprendre et de prédire la crise d'ébullition sous l’effet d’un chauffage transitoire rapide de l'eau sous fortes sous-saturations à pression modérée. Des campagnes expérimentales ont été réalisées pour étudier la crise d’ébullition dans de telles conditions au moyen de vidéos et de thermographie IR hautement résolues en temps et en espace. L’analyse de ces données a permis de déterminer la dépendance du flux critique en transitoire rapide en fonction des différents paramètres d’intérêt (temps caractéristique d’excursion de puissance, vitesse d’écoulement, sous-saturation, pression, largeur du canal, longueur de chauffe). De plus, une analyse approfondie de ces données a permis de mettre en évidence les mécanismes sous-jacents à la crise d’ébullition dans ces conditions. En convection forcée et avec de fortes sous-saturations, les bulles générées en paroi présentent un comportement pulsant. Ce phénomène assure un transfert de chaleur efficace depuis la paroi vers le fluide environnant. Le déclenchement de la crise d’ébullition se produit lorsqu’une fine couche de fluide adjacente à la paroi atteint les conditions de saturation. Un modèle développé à partir de ces observations met en évidence deux paramètres adimensionnés utiles pour décrire la nature transitoire du processus ainsi que pour identifier le mode de refroidissement dominant. Grâce à la connaissance du flux critique en régime permanent, le modèle permet d’estimer de manière conservative le flux critique en fonction de la période d’excursion de puissance et du sous-refroidissement. Ce modèle est maintenant prêt à être implémenté dans des codes de simulation pour l’étude des transitoires accidentels
In case of a reactivity insertion accident in an experimental nuclear reactor, heat generation in the core can grow exponentially in time, with a power escalation period ranging from a few to a few hundreds of milliseconds. Due to neutronic and thermohydraulic effects, boiling crisis may arise, possibly leading to an explosive reaction. If the boiling Crisis has been widely investigated in steady-state conditions, this has not been the case for transient heat inputs. The aim of the present work is to understand and to predict the transient flow boiling crisis in the conditions of moderate pressure and high subcooling. To this end, an experimental campaign has been realized making use of space and time highly resolved videos and IR thermography covering a wide range of experimental parameters. The analysis of the massive amount of data produced by these experiments gives a better insight on the dependency of the transient Critical Heat Flux to the different parameters of interest (power escalation period, flow velocity, subcooling, pressure, channel width, heating length). Moreover, their fine analysis enables to highlight the underlying mechanisms. For conditions of forced flow and high subcooling, the bubbles generated at the wall present a pulsating behavior. This specific process leads to an efficient heat transfer from the wall to the neighboring fluid. Boiling crisis is stated to occur when a thin layer of liquid contacting the wall reaches the saturation temperature. Starting from these observations, a model is developed which brings to light two non-dimensional parameters useful to describe the transient nature of the process and the dominant cooling processes. With the knowledge of the steady-state CHF, the model permits to conservatively estimate the value of the Critical Heat Flux for any power escalation period and subcooling. This model is now ready for implementation into simulation codes to investigate nuclear accidental transients

This study deals with technology of abrasive water jet material cutting and influence of cutting head feed rate on surface topography of cut walls with regards to roughness. Eight parameters were chosen based on the CSN EN ISO 4288 standard representing quality of surface after AWJ cutting. When AWJ cutting the chosen material – commercially pure ASTM B265 grade 2 titanium – feed rate was being changed and in order to obtain information about each parameter´s distribution in various depths of the cut, surface composition was evaluated. It was found out that feed rate has significant influence on surface and that the profile elements´ width grows when increasing the feed rate and cut depth. Furthermore, two selected feed rate results were compared to laser beam technology and conclusion for the selected material was made that AWJ cutting is more preferable due to final roughness and no heat affect on the material.

The main goal of this master´s thesis is a proposal of double way heat exchanger with integrated air-vapor mixture cooler and compare of heat transfer surface´s materials. Second goals are solidity dimensioning of this heat exchanger and economic effectiveness of used heat transfer surface´s materials.

It is common practice to design water chiller units and heat exchangers in such a way that they do not operate within the transition region. This is mainly due to the perceived chaotic behaviour as well as the paucity of information in this region. Due to design constraints or change of operating conditions, however, exchangers are often forced to operate in this region. This is even worse for enhanced tubes as much less information within this region is available. It is also well known that the entrance has an influence on where transition occurs, adding to the woes of available information. The purpose of this study is thus to obtain heat transfer and friction factor data in the transition region of fully developed and developing flows inside smooth and enhanced tubes, using water as the working fluid, and to develop correlations from these results. The use of different inlets, tube diameters and enhanced tubes was also investigated with regards to the commencement of transition. Heat transfer and pressure drop data were obtained from six different types of tubes with diameters of 15.88 mm (5/8′′) and 19.02 mm (3/4′′). Low fin enhanced tubes with a fin height to diameter ratio of 0.4 and helix angles of 18◦ and 27◦ were investigated. Heat transfer was obtained by means of an in-tube heat exchanger with the cooling of water being used as the test fluid. Reynolds numbers ranged between 1 000 and 20 000 while Prandtl numbers were in the order of 4 to 6. Uncertainties in heat transfer coefficient and friction factors were on average below 2.5% and 10% respectively. Adiabatic friction factor results showed that the use of different inlets influenced the commencement of transition. The smoother the inlet profile the more transition was delayed, confirming previous work done. The effect of increasing tube diameters had a slight delay in transition. Enhanced tubes caused transition to occur at lower Reynolds numbers which was accounted for by the fin height and not the helix angle. Heat transfer results showed that transition occurred at approximately the same Reynolds number for all the different inlets and enhanced tubes. This was attributed to the secondary flow forces influencing the growing hydrodynamic boundary layer. These secondary flow forces also influenced the laminar heat transfer and diabatic friction factors with both these parameters being higher. Turbulent enhanced tube heat transfer results were higher than those of the smooth tube, with the tube with the greatest helix angle showing the greatest increase. Correlations were developed for all the tubes and their inlets and predicted all the data on average to within 3%.
Thesis (PhD)--University of Pretoria, 2010.
Mechanical and Aeronautical Engineering
unrestricted

This thesis deals with dependence of heat transfer coefficient on rate of air concentration in the water. Main idea appears from gas dissolvability in water depending on pressure, Henry's law and Newton's law of cooling. There had been an experiment made to verify the hypothesis.

The main goal of master’s thesis is a propsal of the heat exchanger. The heat exchanger is double way of water side with the integrated air-vapor mixture cooler. Another aims are heat computation, heat loss computation, solidity dimensioning and selection of a material for a major selection. The last task is about detection of a vapor pressure trought the tube bundle.

[ES] Esta tesis doctoral presenta un estudio de compresores scroll con inyección de vapor (SCVI) para bombas de calor que operan en climas fríos o para aplicaciones de calentamiento de agua a alta temperatura. Para ello, se comparó experimentalmente un SCVI con un compresor de dos etapas de pistones (TSRC) trabajando con R-407C en condiciones extremas. La comparación se realizó en términos de eficiencias del compresor, capacidad, COP y rendimientos estacionales tanto para el modo calefacción como para el modo refrigeración. Los resultados proporcionan una idea general sobre el rango de aplicación de los compresores estudiados y sobre las diferencias en los rendimientos de los compresores. Sin embargo, se identificaron varias limitaciones en la caracterización de los compresores y en el análisis del ciclo. Esto motivó a profundizar en el estudio del ciclo de compresión de dos etapas y sus componentes. El siguiente paso fue realizar un análisis teórico de los ciclos de compresión de dos etapas para aplicaciones de calefacción, en donde se identificó a la presión intermedia y a la relación de inyección como los parámetros del sistema más influyentes sobre el COP. La presión intermedia se optimizó para dos configuraciones de inyección (tanque de separación y economizador) utilizando varios refrigerantes. Basándose en los resultados de la optimización, se propuso una correlación que permite obtener la presión intermedia óptima del ciclo, considerando la influencia del subenfriamiento a la salida del condensador. Además, se analizó la influencia del diseño de los componentes del sistema sobre el COP del ciclo. Posteriormente, el estudio se profundizó a nivel de componentes. El factor más crítico en el sistema es el rendimiento del compresor. Por lo tanto, el siguiente paso fue evaluar la influencia de varios sistemas de compresión con inyección de vapor sobre el COP. Se tomaron en cuenta tres tecnologías de compresores, un SCVI, un TSRC y un compresor scroll de dos etapas (TSSC). Estas tecnologías de compresores fueron caracterizadas y modeladas para estudiar su rendimiento. Para ello, se propuso una nueva metodología para caracterizar compresores scroll con inyección de vapor. Esta metodología permite evaluar el rendimiento del compresor independientemente del mecanismo de inyección que se utiliza en el ciclo. Se identificó una correlación lineal entre la relación de inyección de refrigerante y la relación de compresión intermedia. Esta correlación se utiliza para determinar el flujo másico de inyección en función de la presión intermedia. Posteriormente, se propuso un modelo semi-empírico de compresores scroll y una metodología para extender dicho modelo para compresores scroll con inyección de vapor. Los modelos fueron ajustados y validados usando datos experimentales de cuatro compresores scroll trabajando con R-290 y un SCVI trabajando con R-407C. Finalmente, se comparó un SCVI con dos compresores de dos etapas, un TSSC y un TSRC, trabajando en condiciones extremas. Se optimizó la relación de volúmenes de los compresores de dos etapas. Los resultados muestran que, en las condiciones nominales de funcionamiento (Te=-15 °C, Tc=50 °C), la relación de volúmenes óptima del TSSC es 0.58, y del TSRC es 0.57. El TSSC consigue un COP 6% mayor que el SCVI y un COP 11.7% mayor que el TSRC. Bajo un amplio rango de condiciones de operación, el SCVI presenta una mejor eficiencia y COP para relaciones de presión inferiores a 5. Para relaciones de presión más altas, el TSSC presenta mejor rendimiento y consigue una temperatura de descarga más baja. Se concluye que el SCVI es una solución fácil de implementar, desde el punto de vista del mecanizado, y que permite extender el mapa de trabajo de los compresores de una etapa. Sin embargo, los resultados muestran que la compresión en dos etapas consigue mejorar en mayor medida el COP del ciclo y la capacidad, con una mayor redu
[CA] Aquesta tesi doctoral presenta un estudi de compressors scroll amb injecció de vapor (SCVI) per a bombes de calor que operen en climes freds o per a aplicacions d'escalfament d'aigua a alta temperatura. Per a això, es va comparar experimentalment un SCVI amb un compressor de dues etapes de pistons (TSRC) treballant amb R-407C en condicions extremes. La comparació es va realitzar en termes d'eficiències del compressor, capacitat, COP i rendiments estacionals tant per al mode calefacció com per al mode refrigeració. Els resultats proporcionen una idea general sobre el rang d'aplicació dels compressors estudiats i sobre les diferències en els rendiments dels compressors. No obstant això, es van identificar diverses limitacions en la caracterització dels compressors i en l'anàlisi del cicle. Això va motivar a aprofundir en l'estudi del cicle de compressió de dues etapes i els seus components. El següent pas va ser realitzar una anàlisi teòrica dels cicles de compressió de dues etapes per a aplicacions de calefacció, on es va identificar la pressió intermèdia i la relació d'injecció com els paràmetres del sistema més influents sobre el COP. La pressió intermèdia es va optimitzar per a dues configuracions d'injecció (tanc de separació i economitzador) utilitzant diversos refrigerants. Basant-se en els resultats de l'optimització, es va proposar una correlació que permet obtindre la pressió intermèdia òptima del cicle, considerant la influència del subrefredament a l'eixida del condensador. A més, es va analitzar la influència del disseny dels components del sistema sobre el COP del cicle. Posteriorment, l'estudi es va aprofundir a nivell de components. El factor més crític en el sistema és el rendiment del compressor. Per tant, el següent pas va ser avaluar la influència de diversos sistemes de compressió amb injecció de vapor sobre el COP. Es van prendre en compte tres tecnologies de compressors, un SCVI, un TSRC i un compressor scroll de dues etapes (TSSC). Aquestes tecnologies de compressors van ser caracteritzades i modelades per a estudiar el seu rendiment. Per a això, es va proposar una nova metodologia per a caracteritzar compressors scroll amb injecció de vapor. Aquesta metodologia permet avaluar el rendiment del compressor independentment del mecanisme d'injecció que s'utilitza en el cicle. Es va identificar una correlació lineal entre la relació d'injecció de refrigerant i la relació de compressió intermèdia. Aquesta correlació s'utilitza per a determinar el flux màssic d'injecció en funció de la pressió intermèdia. Posteriorment, es va proposar un model semi-empíric de compressors scroll i una metodologia per a estendre aquest model per a compressors scroll amb injecció de vapor. Els models van ser ajustats i validats utilitzant dades experimentals de quatre compressors scroll treballant amb R-290 i un SCVI treballant amb R-407C. Finalment, es va comparar un SCVI amb dos compressors de dues etapes, un TSSC i un TSRC, treballant en condicions extremes. Es va optimitzar la relació de volums dels compressors de dues etapes. Els resultats mostren que, en les condicions nominals de funcionament (Te=-15 °C, Tc=50 °C), la relació de volums òptima del TSSC és 0.58, i del TSRC és 0.57. El TSSC aconsegueix un COP 6% major que el SCVI i un COP 11.7% major que el TSRC. Sota un ampli rang de condicions d'operació, el SCVI presenta una millor eficiència i COP per a relacions de pressió inferiors a 5. Per a relacions de pressió més altes, el TSSC presenta millor rendiment i aconsegueix una temperatura de descàrrega més baixa. Es conclou que el SCVI és una solució fàcil d'implementar, des del punt de vista del mecanitzat, i que permet estendre el mapa de treball dels compressors d'una etapa. No obstant això, els resultats mostren que la compressió en dues etapes aconsegueix millorar en major mesura el COP del cicle i la capacitat, amb una major reducció de la
[EN] This Ph.D. thesis presents a study of scroll compressors with vapor-injection (SCVI) for heat pumps operating in cold climates or in high-temperature water heating applications. To do so, firstly, an SCVI was experimentally compared with a two-stage reciprocating compressor (TSRC) working with R-407C under extreme conditions. The comparison was made in terms of compressor efficiencies, capacity, COP, and seasonal COP, both for heating and cooling modes. The results give a general idea about the application range of the studied compressors and the differences in the compressors' performance. Nevertheless, several restrictions in the compressors' characterization and the cycle analysis were identified. This motivated us to deepen in the study of the two-stage compression cycle and its components. The next step was performing a theoretical analysis of two-stage compression cycles for heating applications, where the intermediate pressure and the injection ratio were identified as the most influential system parameters on the COP. The intermediate pressure was optimized for two vapor-injection configurations (flash tank and economizer) using several refrigerants. Based on the optimization results, a correlation was proposed that allows obtaining the optimal intermediate pressure of the cycle, considering the influence of the subcooling at the condenser outlet. In addition, a theoretical analysis of the influence of the design of the system components on the COP of the cycle was performed. Once the thermodynamic analysis of the two-stage cycle was carried out, the study was deepened at the component level. The most critical factor in the system is the compressor performance. Hence, the next step was evaluating the influence of several compression systems with vapor-injection on the COP. Three compressor technologies were taken into account, an SCVI, a TSRC and a two-stage scroll compressor (TSSC). These compressor technologies were characterized and modeled in order to study their performance. To do so, a new methodology to characterize SCVI was proposed. This methodology allows evaluating the compressor performance independently of the injection mechanism used in the cycle. A linear correlation was identified between the refrigerant injection ratio and the intermediate compression ratio. This correlation is used to determine the injection mass flow as a function of the intermediate pressure. Then, a semi-empirical model of scroll compressors and a methodology to extend the model for scroll compressors with vapor-injection was proposed. The models were adjusted and validated using experimental data from four scroll compressors working with R-290 and an SCVI compressor working with R-407C. Finally, an SCVI was compared with two two-stage compressors, a TSSC, and a TSRC, working in extreme conditions. The displacement ratio of the two-stage compressors was optimized. Results show that, at the nominal operating conditions (Te=-15 °C, Tc=50 °C), the optimal displacement ratio of the TSSC is 0.58, and of the TSRC is 0.57. The TSSC achieves 6% larger COP than the SCVI and 11.7% larger COP than the TSRC. Under a wide range of operating conditions, the SCVI presents a better efficiency and COP for pressure ratios below 5. For higher-pressure ratios, the TSSC presents better performance and achieves lower discharge temperature. It is concluded that the SCVI is an easy solution to implement from the point of view of machining, which allows extending the working map of the single-stage compressors. However, the results show that the two-stage compression technology gets further improve the COP of the cycle and the capacity, with a greater reduction of the discharge temperature operating under extreme conditions.
I thank the financial support provided by the Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) of Ecuador, through the international scholarship program for postgraduate studies “Convocatoria Abierta 2013 Segunda Fase, Grant No 2015-AR37665”.
Tello Oquendo, FM. (2019). Study of scroll compressors with vapor-injection for heat pumps operating in cold climates or in high-temperature water heating applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/120473
TESIS

This diploma thesis describes the detailed design of heating and hot water heating for a family quest-house. At first the reader is introduced to the designed building, its design and construction elements. The thesis presents the calculation procedure and design of the heating system. This consists of designing radiators, the heat source, the circulating pumps, regulations of the heating system and the design of its security elements. The thesis also describes the design of the heat exchanger for hot water and security. In conclusion, an evaluation of operating costs with the recommended solution for their reduction. The thesis also includes drawing documentation of structural drawings, heating and unrolled schema that is mentioned in the attachment.

The aim of this thesis is to design the heating system for the house, including the design and calculating the required quantity of heat for hot water. The specified heat sources are the heat pump air to water and solid fuel boiler. The task was to design the heating system to the fastest possible return on investment. The initial investment in a heat pump is high so it is necessary to design the heating system as efficiently as possible. The thesis contains a complete project of calculating heat loss of the building, the design of heating surfaces and their heat-technical calculation. There is included the design of the pipe system, the calculation of pressure loss and its regulation. The thesis also includes design of safety equipment, temperature regulation and drawings. On the basis of calculated data was processed economic assessment, which determines the return on investment to the heat pump. Compared to the gas condensing boiler the return on investment will ideally be after five years.

This work is focussed on hydraulic descaling of hot surfaces. Hydraulic descaling is a process when layers of oxides are removed from hot steel surfaces during continuous rolling. High pressure water beam is used. Quality of descaled surfaces is important for final quality of rolled product. Insufficient descaling causes drop of final quality, degradation of rolls and lost of yields. High-pressure water beam has two effects on a scale layer. The first effect is mechanical caused by impact pressure. The second one is a relatively intensive thermal shock depending on a set of parameters (water pressure, nozzle type, distance from the surface, inclination angle, speed of product moving). There are a lot of theories about principles of scales removing. Main task of this work is to make it clear which theory is acceptable and which is just ,,theory”. For this purpose mathematical modelling and experimental work were used. In experimental part, three types of experimental measurement were done. First one, measurement of dynamical effect of water beam – impact pressure. Second one, measurement of temperature drop when a product is passing under the nozzle. Measured data (temperatures) from this measurement are evaluated with inverse task and heat transfer coefficient is obtained. And the third experimental measurement is simulation of whole process of descaling. Quality of descaled surfaces is valuated according to amount of remained oxide scales. Data from firs and second experimental measurement are used as boundary conditions for mathematical modelling. For mathematical simulations, FEM (finite element method) system ANSYS was used. Obtained data from experimental measurement were applied on 2D and 3D models of basic steel material with layer of scale. Influence of theses data on final temperature, stress and strain fields were observed.

The thesis aims to design a device for utilization of waste heat for heating and hot water in NETME Centre in area of FSI VUT in Brno. First of all there is summary of available sources of waste heat and evaluation of serviceability. Next there is design of a device for utilization of waste heat. Design incluades calculation of heat exchangers and selection of particular heat exchangers. It also incluades design of duct system which anables transportation of heated water from heat exchangers to machine room. In machine room is situated storage tank for accumulation of gained waste heat. This storage tank is conected to heating system and to consumption of hot water which anables utilization of waste heat. Finally there is economic evaluation based on amount of gained waste heat, consumption of heat and costs.

The issue of descaling is an important part of the forging and heat treatment of steel and semi products of steel production. Rising of new information and study of this process can increase efficiency and improve the surface quality after descaling. This thesis is focused on the mechanisms of the high pressure hydraulic descaling qualification and study of the chemical compounds of which the scales grown. To achieve all goals of this work and to get a comprehensive view of descaling process, few experimental measurements and numerical analyses were performed. All experimental measurements were focused on obtaining data about fundamental parameters and effects of the hydraulic descaling. The data obtained from measurements were applied to numerical analyses, which aimed to discover a deeper relation and to confirm the experimental results. This thesis can be divided into two main parts. The first part is devoted to parameters of the water jet study. The main studied characteristics of the high pressure hydraulic water jet were heat transfer coefficient and impact pressure at different modes such as standard or pulsating water jet. Experimentally measured data of these parameters were applied in numerical analyses. The numerical analyses were focused on studying the impact of the water jet parameters on the stresses in the oxide scale layers. A further water jet analysis was focused on the influence of the individual parts of the hydraulic system (such as water chamber or stabilizer) on its characteristics. In this part different types of the water chambers in combination with different types of stabilizers on the impact pressure values were investigated. These measurements were supported by fluid flow analysis through the hydraulic system. The second part of this work was focused on getting mechanical properties of the oxide scales from specimens prepared from standard structural steel and specimens from silicon steel. In this thesis, the influence of various parameters and characteristics was studied on these two types of steel. Mechanical properties of oxide scale structures were carried out by the Small Punch Test method. To obtain the fundamental mechanical properties such as Young´s modulus, yield strength and ultimate strength, material parameters based on the measured data were optimized. The whole work was carried out in order to get valuable and comprehensive results about high pressure hydraulic descaling process and influencing factors as well as about oxide scales themselves.

The subject of this diploma thesis is to design space heating system for building with five floors, where the first above ground floor is used as commercial space. Designed building have one underground floor and four above ground floors. Diploma thesis is designed as project of Building Service, specifically that of Heating. This diploma thesis contains calculations of the design heat load, design of radiators and others heating surfaces, hydraulic balancing, generation of domestic hot water, design of heat source, calculations of safety devices and pumps design. Part of this diploma thesis is also conceptual design of regulation.

The aim of the master’s thesis is to design a condensing steam turbine based on given inputs. Firstly, a design and computation of heat balance is made, followed by thermodynamic calculation of steam turbine channel and a design of compensatory piston of axial forces. Last part of the thesis consists of a review of a change of cooling water temperature in condensator on last turbine stages. The structural drawing of longitudinal section of turbine is included as well.

The main purpose of the diploma thesis is the evaluation of the solar system at the BUT FCE and the application of the topic on the specified building. The specified building was the story cellarless kindergarten with flat roof. There were proposed two variants of applications of the solar collectors: the solar heating of warm water or combination of solar heating of warm water with the support of heating.

La brumisation du condenseur à air d’une machine frigorifique permet une augmentation des échanges thermiques avec l’évaporation de l’eau dans l’air ou en paroi, ce qui augmente la puissance frigorifique et diminue le travail de compression. Ce phénomène est appliqué dans le cadre automobile afin d’abaisser la consommation supplémentaire de carburant induite par la climatisation lorsque le véhicule est à l’arrêt ou roule à faible vitesse. Un dispositif de brumisation autosuffisant en eau, peu énergivore et peu encombrant a ainsi été implémenté afin d’impacter le condenseur du système de climatisation d’un véhicule. Une étude de dimensionnement a montré que le dispositif ne devait pas consommer plus de 1 kg.h-1 récupérés à partir des condensats de l’évaporateur. Les buses étudiées (cône creux et jet plat) ont été choisies en fonction de ce critère. Le condenseur de la machine frigorifique a été isolé dans une maquette expérimentale afin de caractériser et optimiser l’effet de la brumisation. Une méthode d’analyse thermique des surfaces impactées a été développée pour caractériser le phénomène de bouchage étant donné que l’échange thermique se fait à la fois par impact sur la surface de l’échangeur et par l’évaporation du film d’eau. Il a ainsi été montré que, sur le long terme, si la surface frontale de l’échangeur est bouchée à 17 %, cela entraîne 45 % de pertes de charge supplémentaires et 20 à 25 % de transfert thermique en moins. Mais le bouchage peut être bénéfique et stocker de l'énergie thermique lorsque la durée de pulvérisation ne dépasse pas 25 minutes. Enfin, au terme de l’étude, le dispositif de brumisation a été implémenté sur le véhicule et des premiers essais ont montré un réel gain apporté par la brumisation, ce qui est encourageant pour une éventuelle industrialisation du dispositif
Spraying the air condenser of a refrigerating unit increases the heat exchange thanks to the evaporation of water in the air or on the wall, which increases the cooling capacity and decreases the compression work. This phenomenon is applied to the automotive context in order to lower the additional fuel consumption induced by the air conditioning when the vehicle is stopped or is at low speed. A self-sufficient, low-energy, space-saving spraying device was thus implemented in order to impact the condenser of the air conditioning system of a vehicle. A sizing study showed that the spraying device should not consume more than 1 kg.h-1 recovered from the condensates on the evaporator. The studied nozzles (hollow cone and flat fan) were therefore chosen according to this criterion. The condenser of the refrigerating unit was isolated in an experimental device to characterize and optimize the water spraying effect. A thermal analysis method of impacted surfaces has been developed to characterize the clogging phenomenon as the heat is exchanged mainly by the surface impact of the exchanger followed by the water film evaporation. For the long term spraying, 17 % clogging area of the exchanger front surface induces 45 % additional pressure drop and around 25 % degradation in the heat transfer. But clogging can be beneficial and store thermal energy when the spraying time does not exceed 25 minutes. Finally, at the end of the study, the spraying device was implemented on the vehicle and first tests showed a real gain brought by spraying, which is encouraging for a possible industrialization of the device

Dans le secteur de l’énergie nucléaire, le séchage des matériaux irradiés (combustible usagé, déchets métalliques, …) avant son transport ou stockage est une étape nécessaire. Ce séchage permet d’éviter tous risques liés à la présence d’eau résiduelle. En effet, même en faible quantité, l’eau peut être à l’origine de la formation d’hydrogène par radiolyse. Elle peut également provoquer une corrosion des matériaux présents (l’enceinte de confinement, la gaine du combustible, …) ou encore une montée en pression par sa vaporisation. Dans le procédé mis en œuvre et préconisé par Orano, le chargement du contenu radioactif dans l’emballage qui servira au transport a lieu sous eau dans la piscine contenant le combustible usé. Une fois vidangée de son eau, l’emballage est mis sous vide primaire, cette baisse de pression provoque la vaporisation de l’eau résiduelle. La compréhension des phénomènes mis en jeu lors de ce séchage à basse pression, notamment les transferts de chaleur et de masse, a été identifiée comme un des verrous à l’optimisation de cette étape. Aussi, l’objectif principal de cette thèse est d’observer, comprendre et quantifier les phénomènes de transfert de chaleur et de masse dans des conditions opératoires similaires à celles du procédé Orano. Pour atteindre ces objectifs, deux approches complémentaires ont été mises en place. Dans un premier temps, un banc d’essai ad hoc a permis d’observer et de quantifier l’influence de paramètres (pression, température, surface d’évaporation, volume d’eau) sur les débits d’évaporation et coefficients d’évaporation obtenus. Pour aller plus loin dans la compréhension de ces observations, un modèle original a été développé sous le logiciel COMSOL. Ces simulations numériques ont permis de hiérarchiser les phénomènes prédominants suivant le mode opératoire choisi pour le séchage
In the nuclear industry, the drying of nuclear fuel before it is transported or stored is a necessary step. This drying prevents any risks associated with the presence of residual water. Indeed, even in small quantities, water can be responsible for the formation of H2 by radiolysis. It can also cause corrosion of the enclosure or pressure rise by its vaporization. In the process of Orano, the loading of fuel rod in the canister used for the transport or storage takes place in immersion in the pool containing the used fuel. Once the water was drained, the canister is vacuumed, this pressure drop causing the vaporization of the residual water. The understanding of the phenomena involved in this vacuum drying, in particular the coupled heat and mass transfers, was identified as one of the keys to optimize this step. The main objective of this thesis is to observe, understand and quantify heat and mass transfer phenomena under conditions similar to those of the Orano process. To achieve these objectives, two complementary approaches are developed. First, an ad hoc test bench allowed to observe and quantify the influence of parameters (pressure, temperature, evaporation area, volume of water) on the evaporations rates and evaporation coefficients obtained. Secondly, an original model was developed with the COMSOL software. These numerical simulations allowed ranking the predominant phenomena according to the procedure chosen for drying

The subject of this thesis is energy storage systems in building services. In the first part the theoretical acquaintance with the nature of energy storage. In the second part has two variants preparation hot water in an apartment building. In the third part of the test solution storage tank of hot water. Development of computational algorithms, comparison of calculation used and the final summary.

Earth dams are commonly used in many nations because of their ease of building and maintenance. This study aims to determine the seepage discharge in an earth dam by building twenty-four models in a hydraulic flume and altering various input parameters. A dam with a central impermeable core and a homogeneous earth dam has been built in a hydraulic flume in the lab. The earth dam also has a filter to prevent the phreatic line from cutting the downstream slope of the dam, which might cause damage. Some of the characteristics studied in this study include upstream slope, downstream slope, longitudinal slope, upstream slope, downstream slope, changing the top and bottom widths of the dam while keeping the upstream and downstream slopes the same, changing the height and length of the earth dam, central core width, filter length, and filter height; and their impact on seepage and the phreatic line. A fluorescent dye was used to identify a phreatic line in the experimental model, then compared to the phreatic line developed from Seep/w in Geostudio software. The numerical analysis results were found to be consistent with the experimental findings. Dupuit's equation, Casagrande's, Schaffernak's, and Pavlovsky's solutions were used to validate homogenous physical experimental and numerical models. The stability of the upstream and downstream slopes of the earth dam was also examined using Slope/w in Geostudio software, which was confirmed to be safe under full reservoir conditions. The temperature measurement was used to investigate the seepage fluctuation in the earth dam. In a hydraulic flume, seventeen models of earth dams were built by altering geometrical and flow input parameters. Temperature measurement along the phreatic line was done using a digital thermometer and compared to the phreatic line produced by Seep/w. The phreatic line derived from the experimental models was identified using a fluorescent dye. Temp/w was used to model temperature variation inside an earth dam due to the convective flow of water. Temperature variation in an earth dam by the experimental model was compared with the contours of temperature obtained using temp/w and were in good agreement. It was discovered that as the longitudinal slope, downstream slope, and dam height are increased, the water flow accelerates, which leads to a rise in temperature variation of the earth dam due to increased convection and vice versa for the upstream slope. With the introduction of an impervious central core in the earth dam, the dam’s temperature reduced significantly due to the reduced flow vi rate of water. The inclusion of a downstream filter stopped the phreatic line from cutting the earth dam's downstream face. The temperature was increased drastically due to an increased water flow rate due to the filter's increased length and thickness. Temperature measurement proved to be a cost-effective method of detecting seepage in an earth dam. The water flux in an earth dam was simulated in a hydraulic flume by altering geometrical and flow input parameters to determine heat and water flux. A Homogeneous, as well as earth dam with a clay core, was built-in a hydraulic flume. Heat flux was calculated in the experimental model using temperature observations. Seep/w was used to calculate water flux, and temp/w was used to calculate heat flux in a finite element model of the earth dam. When comparing homogeneous models to central impermeable core models, a considerable decrease in heat and water flux was observed. When the length and longitudinal slope of the downstream filter was increased, the heat and water flow increased, and vice versa when the upstream slope and clay core thickness were increased. Heat flux measurements proved to be a cost effective option for measuring water flux and seepage in an earth dam.

碩士
國防醫學院
航太醫學研究所
97
英文摘要 Background G-induced loss of consciousness (G-LOC) is defined as a state of sudden, critical reduction of cerebral blood circulation caused by increased G force that shares similar clinical syndromes of syncope. Water drinking has profound hemodynamic effects. Water drinking may raises sympathetic nerve activity and blood pressure substantially in patients with autonomic dysfunction and in older subjects. Though the pressor response of water drinking was attenuated, these phenomena also have been observed in the young healthy subjects. The possible reason is modulation of the baroreflex system. MOTIVATION: This study made use of the head-up tilt (HUT) test to have blood accumulate in the lower body and induce the phenomena of orthostatic intolerance to simulate orthostatic intolerance. In addition, this study further investigated the effects of water drinking on the cardiovascular system and autonomic nervous system by constantly observing the fluctuations in heart rate variability and blood pressure variability. METHODS: A total of 15 male subjects were enrolled in this study (with an age of 25±2 years old, a height of 170±2 centimeters, a weight of 64±6 kilograms, and a body mass index (BMI) of 21.9±1.7). Subjects were randomized into four groups as follows: (1) subjects drank 50ml of water and lay flat for 50 minutes; (2) subjects drank 50ml of water, lay flat for 5 minutes before undergoing the HUT test for 45 minutes, and lay flat again afterward. If subjects showed presyncope symptoms, they would be asked to stop undergoing the test; (3) subjects drank 500ml of water and lay flat for 50 minutes; (4) subjects drank 500ml of water, lay flat for 5 minutes before undergoing the HUT test for 45 minutes, and lay flat again afterward. If subjects showed presyncope symptoms, they would be asked to stop undergoing the HUT test. A monitoring system for cardiovascular function, Task Force Monitor System (CN Systems, Graz Austria), was used to record the changes of heart rate, blood pressure, stroke volume, cardiac output, peripheral vascular resistance, heart rate variability, and blood pressure variability. STATISTICAL ANALYSES: Graphpad Prism 4 software was used to analyze the statistics and diagrams in this study. The differences between two groups were compared by the Student’s T test and the Mann-Whitney rank sun test. The differences between drinking 50ml and 500ml of water were respectively compared to study the effects of water drinking on physiological functions and the influences of water drinking on the HUT test. The values in diagrams were presented as Mean±SEM and p values <0.05 suggested that there were statistical differences between two groups. RESULTS: It was found that when subjects lay flat, the systolic pressure increased (P=0.006), the diastolic pressure increased (P=0.002), the total peripheral vascular resistance increased (P=0.001) while both the cardiac output (P=0.01) and the LF component of SBP (LF-SBP) (P=0.001) decreased on subjects drinking 500ml of water as compared to subjects drinking 50ml of water. In the HUT test, only one subject in the 50ml group and two subjects in the 500ml group showed presyncope symptoms. When comparing subjects drinking 500ml and 50ml of water, it was found that subjects in the 500ml group showed less increase in heart rate (P=0.023), less decrease in stroke volume (P=0.008), less decrease in cardiac output (P=0.008), less increase in total peripheral vascular resistance (P=0.008), less increase in LFnuRRI (P=0.03), less decrease in HFnuRRI (P=0.03), smaller ratio of LFnu/HFnu-RRI (P=0.019), and less increase in LF-SBP (P=0.0001). CONCLUSIONS: We found subjects drinking 500ml of water could attenuate the effect of an increase in heart rate and decrease in cardiac output induced by HUT test. It is inferred that subjects drinking 500ml of water could enhance the ability to maintain their hemodynamic status. Through the HUT test, we also found that subjects drinking 500ml of water showed a higher level of parasympathetic nervous activity. Furthermore, we also found that in an experiment of the effect of water drinking on autonomic nerves, the sensitivity of blood pressure variability was higher than

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
102
In this study, we analyze the optimal heat rejection pressure for a transcritical heat pump water heater system. We analyze the optimal heat rejection pressure at 65 ℃ and 90 ℃water outlet temperature and we discuss the relationship between the refrigerant temperature at the outlet side of the gas-cooler and the optimal heat rejection pressure. We also discuss the equation of the optimal heat rejection pressure in the reference with our experimental data at 65 ℃water outlet temperature. The results showed that the equation of the optimal heat rejection pressure in the reference which varies with gas-cooler outlet refrigeration temperature can predict the optimal heat rejection pressure for our experiment at 65 ℃water outlet temperature.We use regression analysis to analyze our experimental data and get an equation of the optimal heat rejection pressure which varies with gas-cooler outlet refrigeration temperature at 90℃water outlet temperature. The results showed that the equation of the optimal heat rejection pressure can predict the optimal heat rejection pressure for our experiment at 90℃water outlet temperature. We discuss the equation of the optimal heat rejection pressure which varies with gas-cooler outlet refrigeration temperature at 90℃water outlet temperature with our experimental data at 65℃water outlet temperature. The results showed that the maximum error of 11.36% between two of water outlet temperature, which means significantly different.

The need for alternative sources of energy with low to zero emissions has led to the development of polymer electrolyte membrane fuel cells. PEM fuel cells are electro-chemical devices that convert chemical energy to electricity by using hydrogen as the fuel and oxygen as the oxidant with water as the byproduct of this reaction. One of the major barriers to the commercialization of these cells is the losses that occur at the cathode due to the slow oxygen diffusion and sluggish electrochemical reaction, which are further amplified by the presence of liquid water. Numerous numerical and mathematical models are found in the literature, which investigate the transport phenomena in the cathode and their effects on the cell performance. In this thesis, the discussion of a two-dimensional, steady state, half cell model is put forward. The conservation equations for mass, momentum, species charge and energy are solved using the commercial software COMSOL Multiphysics. The conservation equations are applied to the cathode bipolar plate, gas diffusion layer and catalyst layer. The flow of gaseous species are assumed to be uniform in the channel. The catalyst layer is assumed to be composed of a uniform distribution of catalyst, liquid water, electrolyte, and void space. The Stefan-Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Due to the low relative species' velocity, the Darcy law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is used to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. A sensitivity analysis is carried out to investigate the effects of pressure drop in the channel, permeability, inlet relative humidity and shoulder/channel ratio on the performance of the cell. Electron transport is shown to play an important role in determining the overall performance of the cathode. With a serpentine flow field, the oxygen consumption occurs more aggressively at the areas under the land since electrons are readily available at these areas. In addition, the reaction increases along the catalyst layer thickness and occurs more rapidly at the catalyst layer/membrane interface. The losses due to electron transport are much higher than those due to the proton transport. The sensitivity analysis put forward illustrated that with the increase of pressure drop along the channel flow field, the performance of the cell and liquid water removal are enhanced. Similarly, an increase in permeability of the porous material results in an increase in liquid water removal and cell performance. Further, the investigation of the inlet relative humidity effects revealed that the electrolyte conductivity has a significant effect on the performance up to a point. On a similar fashion, a decrease in shoulder/channel width ratio leads to an increase in performance and an increase in the leakage between neighboring channels. Finally, the addition of heat is shown to have a negative effect on the cell performance. Some recommendations can be drawn from the results of this thesis. It is recommended to develop a model to study the flow in the channel flow field in order to investigate the effects of the channel flow on the transport of species in the cell. Further, the geometry of the channel should be studied. Finally, the production of water should be analyzed. The analysis should be extended to investigate its production in vapor form only and its production as a mixture of vapor and liquid.

M.Ing.
Heat transfer and pressure drop characteristics during in-tube condensation of nonazeotropic mixtures of R22/R142b in a smooth helically coiled copper tube with an inside diameter of 8.11 mm are investigated. The experimental results are compared with prediction from correlation. The coefficient of performance of.the heat pump built and used for experiments has been studied. The mass flux of the refrigerant was varied during the course of the experiments. At similar mass flow rate of fluids, the average heat transfer coefficients for mixtures were lower than those for pure refrigerant R22 used as reference for comparison. Also, the heat transfer coefficients of all the refrigerants increased with increasing mass flux.

Thesis (PhD)--University of Pretoria, 2009.
ENGLISH ABSTRACT: It is common practise to design water chiller units and heat exchangers in such a way that they do not operate within the transitional region. Due to design constraints or change of operating conditions, however, exchangers are often forced to operate in this region. This is even worse for enhanced tubes as much less information within this region is available. It is also well known that the entrance has an influence on where transition occurs, adding to the woes of available information.
Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University

This study consists of an experimental investigation into the fluid flow and heat transfer aspects of microchannels. Rectangular copper microchannels of hydraulic diameters 1.05 mm, 0.85 mm and 0.57 mm were considered. Using water as the working fluid, heat transfer and pressure drop characteristics were determined under a constant surface heat flux for different inlet configurations in the laminar and transitional regimes. Three inlet geometries were experimentally investigated: a sudden contraction inlet, a bellmouth inlet and a swirl-generating inlet. The influence of the inlet conditions on the pressure drop, Nusselt number and critical Reynolds number was determined experimentally. Pressure drop results showed good agreement with existing correlations for adiabatic conditions. Diabatic friction factor results for the sudden contraction and bellmouth inlets were overpredicted when using the friction factor results from literature. It is noted that a relationship between the pressure drop and heat flux existed in the laminar regime, where an increase in the heat input resulted in a decrease in the friction factor. The bellmouth inlet condition showed an enhancement of the heat transfer in the transition regime compared with the sudden contraction inlet. The critical Reynolds number for the onset of transition for the sudden contraction inlet was found to be approximately 1 950, with a sharp rise to the turbulent regime thereafter. The bellmouth inlet influenced the originating point of the transition regime, which commenced at a Reynolds number of approximately 1 600. A smoother and more gradual increase to the turbulent regime was observed as an effect of the bellmouth inlet over the sudden contraction inlet. The swirl-generating inlet condition produced higher friction factor results in all three flow regimes. Transition occurred at a Reynolds number of approximately 1 500 and the turbulent regime was quickly ii reached thereafter. The turbulent regime friction factor was found to be significantly higher with the swirl inlet compared with both the sudden contraction and bellmouth inlets. Nusselt numbers continued to increase until the onset of the transition regime, and did not converge to a constant value as stated in theory. Similar enhancement of the transition regime with the bellmouth inlet was observed for the Nusselt numbers as with the friction factors. The initial turbulent regime results followed the trend of the theory for both the sudden contraction and bellmouth inlet conditions for most of the data sets, with deviation occurring in some of the 0.57 mm test cases. The swirl inlet Nusselt number results were significantly underpredicted by the theory in the early turbulent regime.
Dissertation (MEng)--University of Pretoria, 2014.
gm2014
Mechanical and Aeronautical Engineering
unrestricted

At Oregon State University the Multi-Application Small Light Water Reactor (MASLWR) integral effects testing facility is being prepared for safety analysis matrix testing in support of the NuScale Power Inc. (NSP) design certification progress. The facility will be used to simulate design basis accident performance of the reactor's safety systems. The design includes an initially evacuated, high pressure capable containment system simulated by a 5 meter tall pressure vessel. The convection-condensation process that occurs during use of the Emergency Core Cooling System has been characterized during two experimental continuous blowdown events. Experimental data has been used to calculate an average heat transfer coefficient for the containment system. The capability of the containment system has been analytically proven to be a conservative estimate of the full scale reactor system.
Graduation date: 2013

碩士
國立臺灣海洋大學
機械與機電工程學系
103
The variations of temperature dependent properties of water are studied especially at saturation state and near the critical point. The thermal conductivity as well as viscosity is observed to appear a minimum in the supercritical region, and the relations to pressure have been developed. This study is also interested in the thermal performance of heat exchangers established by Taipower Company. Three cases have been conducted at subcritical and supercritical pressures. Through a series of calculations, the overall heat transfer coefficient can be estimated. When the temperature falls in the low or high regime, the error is around 10%. Whereas the error increases up to 50% while the range of temperature includes either the saturation or pseudo-critical conditions. Similar results were detected in many literatures. Furthermore, the heat transfer coefficients obtained in the present code are compared favorably with the experimental data by China in both tube and annular sides. Finally, the absence of applied heat flux in the present formulas may be expected to play an important role in the further thermal analysis. Nusselt number is an index of heat transfer ability. Some famous empirical correlations were investigated, but none of them can fit the data in the neighborhood of critical point. In addition, the phenomenon of heat transfer deterioration (HTD) was observed near the pseudo critical condition which may result in crack of a boiler tube. A computing program coded in Visual-Basic has been developed to simulate the thermal behavior inside the heated tube. The predicted temperature is made to compare favorably with experimental results. Referencing the facilities in many foreign countries, some suitable sizes of test piece and the installation of thermocouples are recommended. The operating condition including temperature, pressure, mass flux as well as power supply is all investigated which provides Taipower Company to construct the test apparatus

碩士
國立高雄海洋科技大學
輪機工程研究所
98
Abstract An experimental study that comparatively examined the two-phase flow structures, pressure drops and wall-to-fluid heat transfer properties between the tubes without and with the spiky twisted-tape insert, namely the plain and swirl tubes, was performed to disclose their differential thermal-fluid performances with air-water flows. On-line and post-processed high-speed digital images of air-water two-phase phenomena in plain and swirl tubes were detected to ensure the bubbly flow pattern in plain tube and to visualize their characteristic interfacial structures. Superficial liquid Reynolds number (ReL) and air-to-water mass flow ratio (AW), which were respectively controlled in the ranges of 5000-15000 and 0.0004-0.01, were selected as the governing parameters to characterize the heat transfer performances. The dispersed rising air bubbles in the plain tube and the centrifugal-force induced coherent spiral stream of coalesced bubbles in the core of swirl tube modify the pressure-drop and heat-transfer performances from their single-phase conditions to large extents. Selected results of pressure-drop and heat-transfer measurements, flow images and tube-averaged void fractions detected from the plain and swirl tubes with air-water two-phase flows were cross-referenced to illustrate the flow and heat transfer physics responsible for the modified heat transfer enhancement and thermal performance index attributed from the spiky twisted-tape insert. Empirical heat transfer correlations which evaluate the Nusselt numbers over the developed flow regions of the plain and swirl tubes with air-water two-phase flows were generated to assist the industrial applications.

碩士
靜宜大學
食品營養研究所
99
The resistant starch is defined by Food and Agriculture Organization of the United Nations as “The small intestine of healthy people can not be absorbing and degradation products which can enhance the probiotics, decreasing the functional colonic disease and reducing calorie ingestion and then control the body weight”. The purpose of this study were to investigate the effect of osmotic pressure treatment (OPT) and simultaneous heat-moisture phosphorylation treatment (HMPT) on the physicochemical properties, resistant starch content and estimated glycemic index of high amylase starches. Two local starches, including mung bean and water caltrop, and high amylase corn starch (Hylon VII) were treated by both treatment methods for 15-60 min, respectively, in this experiment. The results indicated that the content of resistant starch increased with the increase of processing time in all three tested samples. The treatment of OPT and HMPT promoted the gelatinization temperature (To, Tp, Tc) but decreased the gelatinization enthalpy and pasting viscosity of tested starches. The results also observed that the swelling power and solubility decreased as the treatment time increased on three tested starches. The hardness of mung bean and water caltrop starch gel decreased as those starches were treated by OPT but increased in HMPT mung bean gel. According to X-ray diffraction, the relative crystallinity of starch increased as the starches were treated by OPT and HMPT. The crystal type of Hylon VII corn starch was changed from B-type to Ca-type after OPT treatment. The changes of particle size were observed that the particle size of three tested starches decreased with the increase of HMPT processing time. Moreover, the surface of mung bean starch particle appeared concavity when mung bean starch was processed by OPT. The estimated glycemic index of all processed starches by OPT and HMPT decreased as compared with rice starch