To see the other types of publications on this topic, follow the link: Transfer phenomena.
Dissertations / Theses on the topic 'Transfer phenomena'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Transfer phenomena.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
White, R. P. "Spectroscopic probes for electron transfer phenomena." Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382862.
Full text
2
Weber, Thomas Anthony. "Expatriate knowledge transfer phenomena in defense corporations." Thesis, Indiana Institute of Technology, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10239973.
Full textAbstract:
Expatriate knowledge transfer is often disrupted, which creates a loss of learning for the sending organization. Lack of knowledge transfer also causes a loss of competitive advantage for corporations. This study investigates barriers to knowledge transfer for expatriates in a US-based defense company. This research examines knowledge transfer through the lived experiences of expatriates, focusing on the characteristics of “ability to transfer” and “motivation to transfer” and their representation as “noise” in the communication system. This research uses qualitative methods to explore whether barriers to knowledge transfer exist within a corporation. This phenomenological case study provides a way to understand the social interaction between expatriates and their organization from the expatriates’ perspective. This research contributes to the understanding of the phenomenon around knowledge transfer. The data collected from the expatriates showed many different themes, but the most prevalent was their reliance on their social networks. The most common barrier for knowledge transfer dealt with supervisory interactions and the lack of formal knowledge documentation processes. There were also many other barriers noted by the expatriates, but these barriers were overcome through an expatriate’s focus on personal responsibility.
3
Henkel, Jochen [Verfasser]. "Oxygen Transfer Phenomena in Activated Sludge / Jochen Henkel." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2010. http://d-nb.info/1106115945/34.
Full text
4
Tura, R. "Heat transfer and airflow phenomena in multilouvred ducts." Thesis, Coventry University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374680.
Full text
5
Xiang, Yuanyuan. "Mass Transfer Phenomena in Rotating Corrugated Photocatalytic Reactors." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/30342.
Full textAbstract:
Photocatalysis is a green technology that has been widely used in wastewater treatment. In this work, mass transfer processes in corrugated photocatalytic reactors were characterized both experimentally and through computer simulations. For the experimental work, various drum rotational speeds, reactor liquid volumes and number of corrugations were studied to elucidate their effects on mass transfer phenomena. The mass transfer rate was found to increase with increasing rotational speed. Liquid volumes in the reactor significantly affect the mass transfer rate when 20% of the surface area of the drum was immersed. A higher mass transfer rate was found using the drum with 28 corrugations, which had the lowest mass transfer coefficient when compared to the drums with 13 and 16 corrugations. In the computer simulations, velocity and concentration fields within the corrugated reactors were modelled to explore the characteristics of mass transfer processes. The mass transfer coefficients predicted by the simulations were lower than those measured experimentally due to mass transfer limitations occurring between the corrugation volume and bulk solution in the simulations. Based on mass transfer characteristics, it was determined that the drum with 28 corrugations was the most efficient photocatalytic reactor, and had the lowest mass transfer coefficient among those studied.
6
Vlachopoulos, Georgios. "Phenomena affecting ink transfer in offset lithographic printing." Thesis, Swansea University, 2010. https://cronfa.swan.ac.uk/Record/cronfa42395.
Full textAbstract:
The ink transfer mechanisms in the offset lithographic printing process is consisted by a complex inking roller train which a series of alternately rigid and deformable rollers, are used to precondition and deliver the printing fluid from the ink and fount reservoirs to the image carrier. The lithographic printing inks are complex formulated non-Newtonian fluids with high viscoelastic rheological profile and thixotropic behaviour. A set of ink dilutions was produced based on coldset lithographic printing ink diluted in concentration with Butyl-Diglycol. The rheological profile of the produced inks was examined by detailed rheological characterisation with particular interest on viscosity on tack, thixotropy, viscoelasticity, surface tension, extension and shear viscosity. Further examination established the relationships between shear viscosity and tack focusing on a printing nip between a rigid and elastic roller. A decrease in tack was found to be associated with a decrease in shear and the apparent extension viscosity. Developed imprinting and photographic techniques used to capture and characterise the fundamental phenomena of ribbing and misting associated with ink film splitting at the rollers nip in offset printing. Such techniques used to capture the dynamic profile of those mechanisms on a closed loop distribution system by using a tack meter. The detailed profile of those phenomena was characterised with particular interest on the relationship with the fluids rheological profile and the Capillary number. Extension rheometer was also used to analyse the mechanisms of ribbing and misting phenomena by experimental simulation of a printing nip. A factorial experiment was undertaken based on LI8 Orthogonal Array techniques. The parameters of rollers ratio, ink film thickness, temperature, distribution speed, distribution time and inks viscosity were found to have an influence on misting and ribbing phenomena. Results and analysis established responses and interactions between the process parameters but also between ribbing and misting as essential phenomena with the ink transfer mechanisms in lithographic printing process.
7
Cocchini, Ugo. "Mass transfer phenomena through porous and non-porous membranes." Thesis, Imperial College London, 2001. http://hdl.handle.net/10044/1/8024.
Full text
8
Eccles, Errol R. A. (Errol Ray Antonio). "Flow and heat transfer phenomena in aerated vibrated beds." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74281.
Full textAbstract:
Flow characteristics including resonance phenomena, bubble phenomena, particle circulation and mixing patterns as well as surface-to-bed heat transfer in aerated vibrated beds were studied experimentally. Beds of various model particles were vibrated in the vertical direction with a frequency varying from 0-25 Hz and half-amplitude from 0-4 mm. Alumina, glass beads and molecular sieve particles of sizes ranging from 6 $ mu$m to 3600 $ mu$m were used as the model particles. Air flow rates through holes in the bottom plates varied from 0 to 4 times the minimum fluidizing velocity with one, five or a multiplicity of holes. The resonance phenomenon was characterized by a sudden bed expansion and intense surface agitation; this phenomenon was generally observed only in beds of small particles (d$ sb{ rm p}$ $<$ 250 $ mu$m). Bubble sizes increased while the bubble rise velocities decreased with increasing vibration frequency. An analytical model was developed to predict the resonant frequency assuming that the aerated vibrated bed behaves as a porous piston undergoing reciprocating motion at the applied frequency. Contact heat transfer between an immersed circular cylinder and the vibrated bed was found to be a function of particle circulation which, in turn, depends on the vibration parameters. Particle circulation is maximal at the point at which the bed displayed resonant behaviour. The cylinder-to-bed heat transfer coefficient is also maximal at resonance. A correlation is proposed for the surface-to-bed heat transfer based on these features.
9
Long, Siyuan. "Cast fibrous MMCs : transfer phenomena and micro-structure formation." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362437.
Full text
10
Truong, Bao H. (Bao Hoai). "Effects of surface parameters on boiling heat transfer phenomena." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/76925.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 148-156).
Nanofluids, engineered colloidal dispersions of nanoparticles in fluid, have been shown to enhance pool and flow boiling CHF. The CHF enhancement was due to nanoparticle deposited on the heater surface, which was verified in pool boiling. However, no such work has been done for flow boiling. Using a cylindrical tube pre-coated with Alumina nanoparticles coated via boiling induced deposition, CHF of water was found to enhance up to 40% compared to that of the bare tube. This confirms that nanoparticles on the surface is responsible for CHF enhancement for flow boiling. However, existing theories failed to predict the CHF enhancement and the exact surface parameters attributed to the enhancement cannot be determined. Surface modifications to enhance critical heat flux (CHF) and Leidenfrost point (LFP) have been shown successful in previous studies. However, the enhancement mechanisms are not well understood, partly due to many surface parameters being altered at the same time, as in the case for nanofluids. Therefore, the remaining objective of this work is to evaluate separate surface effect on different boiling heat transfer phenomena. In the second part of this study, surface roughness, wettability and nanoporosity were altered one by one and respective effect on quenching LFP with water droplet was determined. Increase in surface roughness and wettability enhanced LFP; however, nanoporosity was most effective in raising LFP, almost up to 100°C. The combination of the micro posts and nanoporous coating layer proved optimal. The nanoporous layer destabilizes the vapor film via heterogeneous bubble nucleation, and the micro posts provides intermittent liquid-surface contacts; both mechanisms increase LFP. In the last part, separate effect of nanoporosity and surface roughness on pool boiling CHF of a well-wetting fluid, FC-72, was investigated. Nanoporosity or surface roughness alone had no effect on pool boiling CHF of FC-72. Data obtained in the literature mostly for microporous coatings showed CHF enhancement for well wetting fluids, and existing CHF models are unable to predict the enhancement.
by Bao Hoai Truong.
Ph.D.
11
Schmidt, Martin Jurgen. "Bubble phenomena in narrow gap electrolysis cells." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322262.
Full text
12
Hou, Xiaofei. "Numerical modeling of complex heat transfer phenomena in cooling applications." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/309294.
Full textAbstract:
Multiphase and multicomponent flows are frequently encountered in the cooling applications due to combined heat transfer and phase change phenomena. Two-fluid and homogeneous mixture models are chosen to numerically study these flows in the cooling phenomena. Therefore this work is divided in two main parts. In the first part, a two-fluid model algorithm for free surface flows is presented. The two fluid model is usually used as a tool to simulate dispersed flow. With its extension, it may also be applied to large interface (separated) flow. In the second part, the homogeneous mixture model for the multicomponent flow is employed to solve evaporation problems. Finally the simulation is focused on the mixed transitional or turbulent flow with and without evaporation.
In detail, this thesis consists of six chapters. The first chapter is devoted to an introduction to the two-fluid and homogeneous mixture models employed in the multiphase/multicomponent flow. The multiphase classification is explained and the previous works on the two models are reviewed.
The second chapter is mainly focused on the application of the Fractional step method algorithm in the two-fluid model. In addition, the Conservative Level Set method(interface sharpening) is applied to overcome the weakness of the two-fluid model (numerical diffusion of the interface), which is often encountered in the simulations using this model. With the proposed algorithm, the two-fluid model suitable for the dispersed flow is extended to the separated flow.
The homogeneous mixture model is introduced in the third chapter. As an application of this model, different evaporation cases have been tested. A hydrodynamically fully developed laminar flow in a horizontal duct is firstly studied. It is used to verify the model in a laminar flow considering constant physical properties. Water falling films are often applied to enhance the heat transfer. Therefore the second case analyzes the natural convection in a cavity with liquid film (assuming variable physical properties), and validates the falling film model. Finally, a third case is focused
on mixed convective flow interacting with a water falling liquid film. The effects of heat flux on the evaporation rate and the flow structure are investigated employing numerical experiments.
In the fourth chapter, the laminarization phenomena of turbulent forced flow in a vertical pipe with constant heat flux is studied. These studies validate the prediction ability of large eddy simulation in this complex situation. Afterwards additional cases in a long vertical pipe (100 times diameters) are conducted and the results are compared with the existing experimental data. Throughout the whole pipe, the flow state follows a complicated process, which includes turbulent-laminar and laminar-turbulent transitions. This problem is of great significance in industrial applications for it may result in the enhancement or impairment of heat transfer.
Based on the previous verification of the model in turbulent and transitional flow, the simulation of the cooling in a uniformly heated vertical tube is conducted in the fifth chapter with an ascending flow of air and a falling film. This case also involves the transitional complex flow and boundary conditions of falling film with simultaneous heat/mass transfer. The variable factors affecting the evaporation and thermal efficiency have been analyzed.
In Appendix C, as an application in engineering of the work developed within the thesis, a series of flows in a complex geometry of a refrigerator chamber without or with fins are simulated to obtain their effects on the flow distribution and mixing feature.
In the last chapter, the main conclusions are summarized and the future works are listed.Debido a la transferencia de calor y de cambio de fase, fenomenología multifase y multicomponente se encuentra en las aplicaciones de refrigeración. Dependiendo de la estructura de interfaz multifase pueden clasificarse como flujo separado (flujo estratificado), de transición o mezclado flujo y flujo disperso. Dependiendo de los diferentes estados de flujo de dos fases, se deben aplicar diferentes modelos. La presente tesis se centra principalmente en flujo separado. Modelos de mezcla homogénea de dos fluidos se emplean para simular fenómenos de enfriamiento en multifase. Este trabajo se divide en dos partes principales. En la primera parte, un algoritmo de modelo de dos fluidos de la superficie libre se presenta. El modelo de dos fluidos se utiliza generalmente como una herramienta para simular flujo disperso. En la segunda parte, el modelo de mezcla homogénea para flujo multicomponente se emplea para resolver el problemas de evaporación. Finalmente se simulan flujos turbulentos con influencia de la fuerza de flotabilidad. El objetivo a largo plazo es acoplar los dos modelos, que podrían resolver todos los regímenes de flujo y tendrian aplicación en problemas industriales. La presente tesis se compone de seis capítulos. El primer capítulo está dedicado a una introducción a los modelos de mezcla homogénea de dos fluidos empleados en el flujo multifásico / multicomponente. La clasificación de múltiples fases se explica y se revisa la bibliografia existente. El segundo capítulo se centra principalmente en la aplicación del Fractional Step Method en bifasico. Con el algoritmo propuesto, el modelo de dos fluidos adecuado para el flujo disperso se extiende al flujo separado. El modelo para mezcla homogénea se introduce en el tercer capítulo con las mismas ecuaciones de masa, cantidad de movimiento, energía y concentración. Se aplica en casos de evaporación y condensación. El flujo laminar completamente desarrollado en un conducto horizontal se estudia en primer lugar considerando propiedades físicas constantes para verificar el modelo en un flujo laminar. La simulacion de convección natural en una cavidad con propiedades físicas variables y película de líquido se realiza numéricamente para validar el modelo de película descendente. Finalmente, el flujo de convección mixta se investiga en un film descendente. Los efectos de los diferentes parámetros en la evaporación y el flujo son investigados mediante experimentos numéricos. En el cuarto capítulo, la laminarización de flujo turbulento forzado en un tubo vertical con flujo de calor constante se estudia para validar la capacidad de predicción de los modelos LES en el flujo de convección mixta de transición turbulenta-laminar con fuerte fuerza de flotación. Se llevan a cabo estudios numericos y los resultados se comparan con los datos experimentales existentes. A lo largo de toda el conducto, el estado de flujo sigue un proceso complicado, que incluye turbulencia.
13
Prinos, Panagiotis. "A study of momentum transfer phenomena in compound channel flows." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/4968.
Full text
14
Worm, Steven Lee. "Experimental measurement of heat transfer phenomena in a solid adsorbent." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/16487.
Full text
15
Mielke, Eric. "Study on the Transport Phenomena in Complex Micro-Reactors." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36040.
Full textAbstract:
Continuous processing in the pharmaceutical and fine chemical industries, particularly in micro/milli-scale reactors, has been a topic of interest in literature in recent years due to the advantages offered over batch reactions. One such advantage is the enhanced transport properties of operating at smaller scales, although the quantification of the transport phenomena is not straightforward when wall and entrance effects cannot be neglected.
In the first study presented, various micro-mixer geometries and scales were considered to increase the mixing efficiency in liquid-liquid systems of diverse interfacial tensions for fast reactions. The conditions were varied over different flow regimes; including slug flow, parallel flow, and drop flow. A mass-transfer-limited test reaction was used to evaluate the overall volumetric mass transfer coefficients (Korga) as a function of the average rate of energy dissipation (ε) for each mixer design. The onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers for low interfacial-tension systems (i.e., n-butanol-water). In the drop flow regime for energy dissipation rates of around 20 to 500 W/kg, Korga values ranged from approximatively 0.14 to 0.35 s-1 and 0.004 to 0.015 s-1 for the relatively low and high interfacial-tension (i.e., toluene-water) systems, respectively.
The second investigation explored the heat transfer properties of a FlowPlate® system by Ehrfeld Mikrotechnik BTS. First, in a non-reactive system with rectangular serpentine channels (d_h<1mm, 400
16
Hoogenboezem, Teunis Adrianus. "Heat transfer phenomena in flow through packed beds / Teunis Adrianus Hoogenboezem." Thesis, North-West University, 2006. http://hdl.handle.net/10394/4300.
Full textAbstract:
In order to simulate the thermal-fluid performance of a pebble bed reactor such as the PBMR, heat transfer phenomena in packed beds must be characterized. In the pseudo-heterogeneous simulation approach that is often employed, the bed is not modeled as a single lumped entity but rather is discretized into control volumes, each with a given homogeneous porosity. Therefore, the Nusselt number characteristics for pebble-to-fluid heat transfer must be investigated for homogeneous porosity packed beds.
The purpose of this study is to measure the heat transfer coefficient (Nusselt number) for pebble-to-fluid convection heat transfer for a given set of discrete homogeneous porosities and then compare it with existing correlations.
A literature study was conducted and it was found that several heat transfer phenomena exist in a packed bed and that in order to obtain useful results it is necessary to isolate connective heat transfer from conduction and radiation heat transfer. Convective heat transfer for packed beds can be divided into the following two divisions, namely:
• Pebble-to-fluid heat transfer;
• Wall-to-fluid heat transfer;
In this study the heat transfer coefficient (Nusselt number) for pebble-to-fluid convection heat transfer is measured for three discrete homogeneous porosity test sections ( 0.36; 0.39; 0.45) that form part of the PBMR High Pressure Test Unit (HPTU). As part of the experimental procedure the standard uncertainty due to the instrument inaccuracies were determined. Data from the physical tests was systematically processed to obtain results of Nusselt number as a function of Reynolds number. From the processed data the relevant non-dimensional parameters could be plotted along with the standard uncertainty in each data point. Repeatability of the data as well as the comparison of the data with correlations from the literature survey is also done and graphically illustrated.
From the results it can be concluded that the HPTU test facility provides good quality results with high repeatability and relatively low uncertainty. The maximum standard uncertainty of 10.88% implies that the data measured on the HPTU is reliable. However, significant differences were found in the values measured for the homogeneous porosity test sections versus that of randomly packed beds that were employed in studies by other authors.Thesis (M.Ing. (Mechanical Engineering)--North-West University, Potchefstroom Campus, 2007.
17
Bahmanyar, Hossein. "Drop breakage and mass transfer phenomena in a rotating disc contactor." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253321.
Full text
18
MATSUBARA, Shigeki, and Yasuyoshi INAGAKI. "Incremental Transfer in English-Japanese Machine Translation." The Institute of Electronics, Information and Communication Engineers, 1997. http://hdl.handle.net/2237/11131.
Full text
19
Ali, Rashid. "Phase Change Phenomena During Fluid Flow in Microchannels." Doctoral thesis, KTH, Tillämpad termodynamik och kylteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26796.
Full textAbstract:
Phase change phenomena of a fluid flowing in a micro channel may be exploited to make the heat exchangers more compact and energy efficient. Compact heat exchangers offer several advantages such as light weight, low cost, energy efficiency, capability of removing high heat fluxes and charge reduction are a few to mention. Phase change phenomena in macro or conventional channels have been investigated since long but in case of micro channels, fewer studies of phase change have been conducted and underlying phenomena during two-phase flow in micro channels are not yet fully understood. It is clear from the literature that the two-phase flow models developed for conventional channels do not perform well when extrapolated to micro scale. In the current thesis, the experimental flow boiling results for micro channels are reported. Experiments were conducted in circular, stainless steel and quartz tubes in both horizontal and vertical orientations. The internal diameters of steel tubes tested were 1.70 mm, 1.224 mm and the diameter of quartz tube tested was 0.781 mm. The quartz tube was coated with a thin, electrically conductive, transparent layer of Indium-Tin-Oxide (ITO) making simultaneous heating and visualization possible. Test tubes were heated electrically using DC power supply. Two refrigerants R134a and R245fa were used as working fluids during the tests. Experiments were conducted at a wide variety of operating conditions. Flow visualization results obtained with quartz tube clearly showed the presence of confinement effects and consequently an early transition to annular flow for micro channels. Several flow pattern images were captured during flow boiling of R134a in quartz tube. Flow patterns recorded during the experiments were presented in the form of Reynolds number versus vapour quality and superficial liquid velocity versus superficial gas velocity plots. Experimental flow pattern maps so obtained were also compared with the other flow pattern maps available in the literature showing a poor agreement. Flow boiling heat transfer results for quartz and steel tubes indicate that the heat transfer coefficient increases with heat flux and system pressure but is independent on mass flux and vapour quality. Experimental flow boiling heat transfer coefficient results were compared with those obtained using different correlations from the literature. Heat transfer experiments with steel tubes were continued up to dryout condition and it was observed that dryout conditions always started close to the exit of the tube. The dryout heat flux increased with mass flux and decreased with exit vapour quality. The dryout data were compared with some well known CHF correlations available in the literature. Two-phase frictional pressure drop for the quartz tube was also obtained under different operating conditions. As expected, two-phase frictional pressure drop increased with mass flux and exit vapour quality.QC 20101206
20
Yamauchi, Akira. "Heat transfer phenomena and mold flux lubrication in continuous casting of steel /." Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3121.
Full text
21
Koren, Chai. "Modeling conjugate heat transfer phenomena for multi-physics simulations of combustion applications." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC001/document.
Full textAbstract:
Dans un souci d’optimisation des fours industriels et de réduction des émissions de gaz à effet de serre,l’oxy-combustion est considérée comme l’une des solutions d’avenir. Les conditions existantes dans les chambres d’oxycombustion créent une interaction forte entre les différents phénomènes : Combustion,turbulence et transferts de chaleur. Pour mieux dimensionner les configurations futures il est nécessaire de pouvoir étudier la physique qui y règne, et ce pour un coût et un temps de retour raisonnables. De tels études nécessitent l’emploi d’outils de simulation de haute fidélité,et afin de modéliser les interactions inter-phénomènes à un coût acceptable le couplage de codes est utilisé. C’est avec cet objectif que les travaux présentés dans ce manuscrit se concentrent sur la mise au point d’une méthodologie de couplage entre codes d’écoulements réactifs et de transfert de chaleur dans les parois pour la réalisation de simulations de haute-fidélité massivement parallèles prédictives des chambres futuresOxycombustion is seen as one mean to attain the wished goals in terms of efficiency optimisation and Greenhouse Effect Gases emissions reduction for industrial furnaces. The extreme operating conditions, high pressure and temperature, lead to a strong interaction between the different phenomena which take place inside the combustion chambe r: Combustion, turbulence and heat transfer. To better design these futur oxyfuel processes, a mean to study the related physics with a reasonable computational cost and return time. Such studies require the use of high-fidelity numerical resolution tools, and in order to model the multi-physics interaction in a cost efficient way, code coupling. The operating conditions being extreme : High pressure and temperature, a strong interaction exists between the different phenomena occuring inside the chamber. To better understand the physics inside oxycombustion chambers,a multiphysics high-fidelity simulation methodology is developped
22
Xiao, Rong Ph D. Massachusetts Institute of Technology. "Wetting and phase-change phenomena on micro/nanostructures for enhanced heat transfer." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/79285.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2013.Page 76 blank. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 71-75).
Micro/nanostructures have been extensively studied to amplify the intrinsic wettability of materials to create superhydrophilic or superhydrophobic surfaces. Such extreme wetting properties can influence the heat transfer performance during phase-change which is of great importance in a wide range of applications including thermal management, building environment, water harvesting and power production. In particular, superhydrophilic surfaces have been of interest to achieve thin film evaporation with high heat fluxes. Meanwhile, superhydrophobic surfaces with dropwise condensation promises higher heat transfer coefficients than typical filmwise condensation. My thesis work aims at improving fundamental understanding as well as demonstrating practical enhancements in these two areas. A key challenge to realizing thin film evaporation is the ability to achieve efficient fluid transport using superhydrophilic surfaces. Accordingly, we developed a semi-analytical model based on the balance between capillary pressure and viscous resistance to predict the propagation rates in micropillar arrays with high aspect ratios. Our experimental results showed good agreement with the model, and design guidelines for optimal propagation rates were proposed. For micropillar arrays with low aspect ratio and large spacing between pillars, however, we identified that the microscopic sweeping of the liquid front becomes important. We studied this phenomenon, explained the effect of such microscale dynamics on the overall propagation behavior, and proposed a strategy to account for these dynamics. While these propagation studies provide a means to deliver liquid to high heat flux regions, we investigated a different configuration using nanoporous membrane that decouples capillarity from the viscous resistance to demonstrate the potential heat dissipation capability. With nanoporous membranes with average pore diameters of 150 nm and thicknesses of 50 [mu]m, we achieved interfacial heat fluxes as high as 96 W/cm2 via evaporation with isopropyl alcohol. The effect of membrane thickness was studied to offer designs that promise dissipation of 1000 W/cm 2 . Meanwhile, we developed new metrology to measure transient heat transfer coefficients with a temporal resolution of 0.2 seconds during the evaporation process. Such a technique offers insight into the relationship between liquid morphology and heat transfer behavior. Finally, for enhanced condensation, we demonstrated immersion condensation using a composite surface fabricated by infusing hydrophobic oil into micro/nanostructures with a heterogeneous coating. With this approach, three key attributes to maximize heat transfer coefficient, low departure radii, low contact angle, and high nucleation density, were achieved simultaneously. We specifically elucidated the mechanism for the increase in nucleation density and attribute it to the combined effect of reduced water-oil interfacial energy and local high surface energy sites. As a result, we demonstrated approximately 100% enhancement in heat transfer coefficient over state-of-the-art superhydrophobic surfaces with the presence of non-condensable gases. This thesis presents improved fundamental understanding of wetting, evaporation, and condensation processes on micro/nanostructures as well as practical implementation of these structures for enhanced heat transfer. The insights gained demonstrate the potential of new nanostructure engineering approaches to improve the performance of various thermal management and energy production applications.
by Rong Xiao.
Ph.D.
23
Simonetti, Marco. "Study of convective heat transfer phenomena for turbulent pulsating flows in pipes." Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2057/document.
Full textAbstract:
Dans le but de réduire la consommation en carburant et les émissions de CO2 des moteurs à combustion interne, un des leviers, qui a intéressé diffèrent acteurs dans le secteur automobile, est la récupération de l’énergie thermique disponible dans les gaz d’échappement. Malgré différents technologie ont été investigués dans le passé; les transferts de chaleur qui apparient dans les gaz d’échappement n’ont pas encore étés suffisamment étudiés. Le fait que les échanges de la chaleur apparent dans des conditions pulsatives, notamment due aux conditions de fonctionnement moteur, rende les connaissances acquis jusqu’à présent limités et ne pas exploitables. A l’état actuel on n’est pas capable de pouvoir prédire le transfert thermique convectif des écoulements pulsé. Les travaux de cette thèse s’instaurent dans la continuité de ce besoin, l’objectif principal est donc l’étude expérimentale du transfert thermique convectif des écoulements turbulent pulsés dans un conduit cylindrique. La première partie de ce travail a été consacrée à le dimensionnement d’un moyen d’essais permettant la création d’un écoulement pulsé type moteur; en suite différents méthodes de mesures ont étés développes afin de connaitre les variations instantanés de vitesse et température de l’écoulement. Plusieurs essais ont été reproduits afin de caractériser l’impact de la pulsation sur le transfert de la chaleur. Les résultats expérimentaux ont été analysés avec deux approches différentes: dans un premier temps une approche analytique 1D a permis de mettre en évidence le mécanisme principal responsable de l’amélioration du transfert thermique convectif,ainsi, il a fourni des éléments supplémentaires pour le futur développement de modèles mathématiques plus adaptés à la prédiction des transferts d’énergie. En suite une approche 2D, supporté d’une phase de modélisation numérique, a permis de caractériser le mécanisme de transport radial d’énergie thermiqueWaste Energy Recovery represents a promising way to go further in fuel saving and greenhouse emissions control for Internal Combustion Engine applications. Although several technologies have been investigated in the past few years, the convective heat transfers, playing an important role in the energy exchanges at the engine exhaust, has not receive enough attention. Heat transfers, in such applications, occur in pulsating conditions because of the engine operating conditions, making thus the actual knowledge of the heat transfer phenomena limited and not exploitable. Nowadays there is not any model capable to predict convective heat transfers for pulsating flows. In this context, the present thesis addresses the purpose to study the convective heat transfer phenomena, by an experimental approach, occurring for turbulent pulsating flows in pipes. In the first part of this work, an experimental apparatus has been designed to reproduce an exhaust type pulsating flow in fully managed conditions, as well as, several measurement techniques have been developed to know the instantaneous profiles of air temperature and velocity. Many experiments have been performed in order to characterize the impact of the flow pulsation on the convective heat transfers. In the second part of this work, the experimental results have been analyzed with two different approaches: firstly, with a 1D assumption the time-average convective heat transfers has been computed, and the major mechanism responsible of the heat transfer enhancement has been pointed out. Furthermore, it has been possible to highlight the mathematical term representative of such mechanism, which should be accounted in future to define a more adapted numerical model for the heat transfer prediction. In a second phase with a 2D assumption, and, with an energy and a fluid-mechanic computational phase, the radial transport of thermal energy has been characterized for a pulsating flow
24
Kawai, Shunsuke. "Numerical Analysis on Free Convection and Mass Transfer Phenomena in Electrochemical System." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/88043.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第15006号
工博第3180号
新制||工||1478(附属図書館)
27456
UT51-2009-R730
京都大学大学院工学研究科機械理工学専攻
(主査)教授 木田 重雄, 教授 稲室 隆二, 教授 中部 主敬
学位規則第4条第1項該当
25
Mitchell, William James. "Transport phenomena in viscous flow and particle motion in fluidized beds /." Title page, table of contents and abstract only, 1988. http://web4.library.adelaide.edu.au/theses/09ENS/09ensm682.pdf.
Full text
26
Li, Yichen. "Phase-field Modeling of Phase Change Phenomena." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99148.
Full textAbstract:
The phase-field method has become a popular numerical tool for moving boundary problems in recent years. In this method, the interface is intrinsically diffuse and stores a mixing energy that is equivalent to surface tension. The major advantage of this method is its energy formulation which makes it easy to incorporate different physics. Meanwhile, the energy decay property can be used to guide the design of energy stable numerical schemes.
In this dissertation, we investigate the application of the Allen-Cahn model, a member of the phase-field family, in the simulation of phase change problems. Because phase change is usually accompanied with latent heat, heat transfer also needs to be considered. Firstly, we go through different theoretical aspects of the Allen-Cahn model for nonconserved interfacial dynamics. We derive the equilibrium interface profile and the connection between surface tension and mixing energy. We also discuss the well-known convex splitting algorithm, which is linear and unconditionally energy stable. Secondly, by modifying the free energy functional, we give the Allen-Cahn model for isothermal phase transformation. In particular, we explain how the Gibbs-Thomson effect and the kinetic effect are recovered. Thirdly, we couple the Allen-Chan and heat transfer equations in a way that the whole system has the energy decay property. We also propose a convex-splitting-based numerical scheme that satisfies a similar discrete energy law. The equations are solved by a finite-element method using the deal.ii library. Finally, we present numerical results on the evolution of a liquid drop in isothermal and non-isothermal settings. The numerical results agree well with theoretical analysis.Master of Science
Phase change phenomena, such as freezing and melting, are ubiquitous in our everyday life. Mathematically, this is a moving boundary problem where the phase front evolves based on the local temperature. The phase change is usually accompanied with the release or absorption of latent heat, which in turn affects the temperature. In this work, we develop a phase-field model, where the phase front is treated as a diffuse interface, to simulate the liquid-solid transition. This model is consistent with the second law of thermodynamics. Our finite-element simulations successfully capture the solidification and melting processes including the interesting phenomenon of recalescence.
27
Kapadia, Jaimin Maheshbhai. "DNA transfer in the soil bacterium Rhodococcus." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/honors/565.
Full textAbstract:
Gene transfer plays an important role in bacterial evolution. Especially in an under explored species like Rhodococcus, a type of bacteria found in the soil. Rhodococcus has several applications in the pharmaceutical industry and in the production of antibiotics. Rhodococcus possess several unique sets of properties which makes it beneficial to have a reliable method of producing mutants of Rhodococcus. The goal of the experiment was to find an efficient way of forming Rhodococcus colonies with kanamycin resistant genes. The project began from an unexpected observation from an earlier experiment with Rhodococcus strain MTM3W5.2. where I attempted to transform this strain with a transposon via electro-transformation. The colonies that grew/ appeared transformants were screened to confirm the presence of kanamycin gene, however there was no amplified DNA seen on the PCR gel (i.e. absence of the kanamycin gene). The electro-transformant colonies were selected on LB plates containing different higher concentrations of kanamycin. Then the appeared transformants were again screened via disk diffusion assay and were classified into 3 different kanamycin resistant phenotypes. Majority of the “C” phenotypic colonies (i.e., high level resistance to kanamycin) appear to contain the kanamycin gene, but these colonies were less in numbers. This led us to try another method of gene transfer which is conjugation. Conjugation was carried on a double selection antibiotic plate containing both chloramphenicol (30 µg) and kanamycin (100 µg). The transconjugate colonies that appeared on the double selection plates were also screened by PCR, but none of the colonies had amplified DNA suggesting absence of the kanamycin gene. The colonies seen on the double selection plate were possibly due to spontaneous mutation or some type of unknown phenotypic variation. However, in the future, double selection plates with higher concentrations of antibiotics can possibly give us transconjugants with kanamycin genes.
28
Kanel, Jeffrey Scott. "Effects of some interfacial phenomena on mass transfer in agitated liquid-liquid dispersions." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/11257.
Full text
29
Frayce, Denis. "Hydrodynamics, heat and mass transfer phenomena in reverberatory furnaces : mathematical modelling and experimentation." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74665.
Full textAbstract:
Following melt alloying and chlorine fluxing in reverberatory-like aluminum holding furnaces, it is common practice to allow the melt to settle for about an hour prior to casting operations. The purpose of this procedure is to allow inclusions to settle to the surface bottom or to float out to an overlying layer of dross. Mathematical modelling of this process reveals that significant natural convection currents are generated, particularly during the early part of this holding period, and that as these currents gradually diminish, so does the rate of precipitation of inclusions. A 6.25 ton pilot scale holding furnace was used to test the model's predictions of changes in metal quality with holding time. Satisfactory agreement was observed between predicted and "LiMCA"$ sp1$ measured changes in inclusion density levels of (Ti-V)B$ sb2$. Both approaches revealed exponential-like decays in inclusion density levels, with time constants in order of 10 to 60 minutes. ftn$ sp1$LiMCA--Liquid Metal Cleanliness Analyzer
30
Mumby, Richard. "The physical and chemical aspects of transfer phenomena in off-set lithographic printing." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396908.
Full text
31
Ortiz, de Gortari A. B. "Exploring 'Game Transfer Phenomena' : a multimodal research approach for investigating video games' effects." Thesis, Nottingham Trent University, 2015. http://irep.ntu.ac.uk/id/eprint/27888/.
Full textAbstract:
Video games are evolving and are becoming ever more immersive. Consequently, it is necessary to understand their effects on gamers’ psychological wellbeing. The impact on cognition, affect and behaviour has mostly been investigated separately and sometimes from narrow approaches that limit the understanding of the video games’ effects. This thesis investigates the effects of playing video games from a novel, multimodal and broad research approach that is termed "Game Transfer Phenomena" (GTP). The Game Transfer Phenomena framework examines the influence of video games on gamers’ sensorial perception, cognitions, and behaviours directly related to video games’ structural characteristic, game content and, in-game activities. A theoretically eclectic approach is taken to explain the interplay of physiological, perceptual, and cognitive mechanisms involved in GTP, mainly informed by socio-cognitive and behavioural theories. Mixed-methods were used in the empirical research. The three qualitative studies presented here were analysed by content and thematic analysis methodologies (n=1,244), and the quantitative online survey using appropriate statistical testing (n=2,362). The specific aims of the thesis were: (i) identify, classify and explain GTP experiences collected in online video game forums divided in three empirical studies, and (ii) investigate the characteristics of GTP, and factors associated with GTP in a cross-cultural online survey with a total sample of English and Spanish Speaking gamers. The results suggest that gamers experience a variety of non-volitional phenomena when not playing. (i) Experiencing thoughts, urges, images, sounds, tactile and kinaesthetic perceptions and sensations associated with the game, (ii) perceiving distorted physical stimuli due to the video game features, (iii) confusing physical stimuli with video game elements, (iv) responding to certain physical stimuli as in the game, and (v) experiencing involuntary body movements and behaviours directly related with the video game. In summary: (i) different gamers reported similar GTP in the same video games, (ii) GTP are in the continuum between normal and pathological phenomena, and appear to reflect failures in cognitive and control inhibition, and neural adaptations, (iii) age and occupation, having a medical condition, gamer type, session length, playing for escape, immersion, exploring, customization and rules and mechanics were significantly associated with GTP, and (iv) the appraisal of GTP were either positive or negative (with one in five players experiencing distress or dysfunction due to their GTP experiences). Findings suggest that resemblances between virtual and physical objects facilitate GTP and these may be strengthened with more advanced technologies. Knowing about particular video game features and their effect on gamers may contribute to taking more informed decisions regarding the psychological, cognitive, physiological and social effects of video games and the technologies that are still to come.
32
Diette, Christophe. "Measurement and analysis of forced convection phenomena in blade cooling channels." Valenciennes, 2003. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/c76547a4-820c-48f8-9717-ced740f0cb38.
Full textAbstract:
Dealing with gas turbine aircraft engines, the Turbine Entry Temperature (TET) is generally targeted as high as possible. Increasing this parameter leads to higher thermodynamic efficiency and power output and reduces the weight-to-thrust ratio and the Specific Fuel Consumption (SFC). Since the maximum permissible TET is determined by the temperature limitations of the turbine assembly, the choice of turbine material and the design of cooling systems applied to turbine blades are essential. This work reports both an experimental and numerical investigation on internal blade cooling cavities. Various cross sections are examined depending on the region of the blade to cool down. Numerous parameters regarding the promoters of turbulence and the flow conditions are varied to find an optimum solution in terms of both heat transfer and pressure losses. Numerical simulations are performed to support the analysis of the flow behaviour. A good agreement is found between the simulations and the aerodynamic measurements. Theoretical diagrams to interpret the flow field are finally proposed. This study provides a better understanding of flow features occuring in cooling channels together with a very detailed database. The later is useful for further numerical validations and the optimisation of cooling cavitiesEn matière de moteurs d'avion à turbine à gaz, une Température d'Entrée de Turbine (TET) aussi élevée que possible est souhaitée. Augmenter sa valeur permet en effet d'obtenir un rendement thermodynamique plus élevé tout en réduisant le rapport poids-poussée et la consommation spécifique (SFC). Parce que la TET maximum permise est liée aux limites de température supportées par les composants de la turbine, le choix des matériaux et la conception des circuits de refroidissement d'aubes sont cruciaux. Cette recherche rend compte d'une étude expérimentale et numérique sur les cavités internes de refroidissement d'aubes. Des sections de passage différentes sont examinées, en fonction de la région de l'aube à refroidir. Plusieurs paramètres en ce qui concerne les promoteurs de turbulence et les conditions de l'écoulement, sont variés pour définir une solution optimale en termes de transfert de chaleur et pertes de charges. Des simulations numériques sont réalisées pour appuyer l'analyse de l'écoulement. La comparaison de ces résultats avec les mesures aérodynamiques se révèle très satisfaisante. Enfin, des diagrammes sont proposés, pour décrire l'écoulement dans chaque cavité étudiée. De cette étude, il ressort une meilleure compréhension des phénomènes mis en jeu dans les cavités de refroidissement, ainsi qu'une base de données détaillée. Cette dernière est utile pour la validation de codes de calcul et l'optimisation des systèmes de refroidissement
33
Raymond, Alexander William. "Investigation of microparticle to system level phenomena in thermally activated adsorption heat pumps." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34682.
Full textAbstract:
Heat actuated adsorption heat pumps offer the opportunity to improve overall energy efficiency in waste heat applications by eliminating shaft work requirements accompanying vapor compression cycles. The coefficient of performance (COP) in adsorption heat pumps is generally low. The objective of this thesis is to model the adsorption system to gain critical insight into how its performance can be improved. Because adsorption heat pumps are intermittent devices, which induce cooling by adsorbing refrigerant in a sorption bed heat/mass exchanger, transient models must be used to predict performance. In this thesis, such models are developed at the adsorbent particle level, heat/mass exchanger component level and system level.
Adsorption heat pump modeling is a coupled heat and mass transfer problem. Intra-particle mass transfer resistance and sorption bed heat transfer resistance are shown to be significant, but for very fine particle sizes, inter-particle resistance may also be important. The diameter of the adsorbent particle in a packed bed is optimized to balance inter- and intra-particle resistances and improve sorption rate. In the literature, the linear driving force (LDF) approximation for intra-particle mass transfer is commonly used in place of the Fickian diffusion equation to reduce computation time; however, it is shown that the error in uptake prediction associated with the LDF depends on the working pair, half-cycle time, adsorbent particle radius, and operating temperatures at hand.
Different methods for enhancing sorption bed heat/mass transfer have been proposed in the literature including the use of binders, adsorbent compacting, and complex extended surface geometries. To maintain high reliability, the simple, robust annular-finned-tube geometry with packed adsorbent is specified in this work. The effects of tube diameter, fin pitch and fin height on thermal conductance, metal/adsorbent mass ratio and COP are studied. As one might expect, many closely spaced fins, or high fin density, yields high thermal conductance; however, it is found that the increased inert metal mass associated with the high fin density diminishes COP. It is also found that thin adsorbent layers with low effective conduction resistance lead to high thermal conductance. As adsorbent layer thickness decreases, the relative importance of tube-side convective resistance rises, so mini-channel sized tubes are used. After selecting the proper tube geometry, an overall thermal conductance is calculated for use in a lumped-parameter sorption bed simulation. To evaluate the accuracy of the lumped-parameter approach, a distributed parameter sorption bed simulation is developed for comparison. Using the finite difference method, the distributed parameter model is used to track temperature and refrigerant distributions in the finned tube and adsorbent layer. The distributed-parameter tube model is shown to be in agreement with the lumped-parameter model, thus independently verifying the overall UA calculation and the lumped-parameter sorption bed model.
After evaluating the accuracy of the lumped-parameter model, it is used to develop a system-level heat pump simulation. This simulation is used to investigate a non-recuperative two-bed heat pump containing activated carbon fiber-ethanol and silica gel-water working pairs. The two-bed configuration is investigated because it yields a desirable compromise between the number of components (heat exchangers, pumps, valves, etc.) and steady cooling rate. For non-recuperative two-bed adsorption heat pumps, the average COP prediction in the literature is 0.39 for experiments and 0.44 for models. It is important to improve the COP in mobile waste heat applications because without high COP, the available waste heat during startup or idle may be insufficient to deliver the desired cooling duty. In this thesis, a COP of 0.53 is predicted for the non-recuperative, silica gel-water chiller. If thermal energy recovery is incorporated into the cycle, a COP as high as 0.64 is predicted for a 90, 35 and 7.0°C source, ambient and average evaporator temperature, respectively. The improvement in COP over heat pumps appearing in the literature is attributed to the adsorbent particle size optimization and careful selection of sorption bed heat exchanger geometry.
34
Hu, Weiwei. "Characterization of hydrodynamic forces and interfacial phenomena in cell culture processes." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1167409370.
Full text
35
Vasic, Aleksander Z. "High temperature properties and heat transfer phenomena for steam at temperatures up to 5000K." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/9641.
Full textAbstract:
Thermodynamic and transport properties and heat phenomena for steam in a high temperature region were examined. First, a set of computer subroutines was developed -the Fraction code, for generating molar fractions of a dissociating steam and gas mixture for a given pressure and temperature. Second, a set of computer subroutines was developed for the computation of all possible combinations of binary diffusion coefficients and of the diffusion coefficient for the component through a gas mixture. Third, steam properties may be evaluated for an ideal gas mixture which includes no effect of chemical reactions-frozed state, or for a non-ideal solution at equilibrium state which includes maximal effects of chemical reactions-effective properties at equilibrium state. A set of computer subroutines was developed-the Frozen Properties code, for evaluating dissociated steam frozen properties for a given pressure and temperature. A computer code, UODH2O (University of Ottawa Dissociation H$\sb2$O code), was developed using a look-up table and interpolation technique to generate effective properties at pressure from 0.01 to 100.00MPa and temperature from 1000 to 5726.85$\sp\circ$C. Based on the semi-empirical model by Nesterenko et al. (1967 a) for dissociated nitrogen tetroxide (N$\sb2$O$\sb4$#2NO$\sb2$ a two-component gas mixture), a method was developed to determine the Nusselt number of a chemically reacting (dissociated) fluid flow. (Abstract shortened by UMI.)
36
Rossi, Giacomo <1990>. "Highlighting Charge Transfer Phenomena in Photo-catalytic Compounds Using Optical and X-ray Techniques." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8398/1/Tesi_Dottorato_Giacomo_Rossi_versione_depositata.pdf.
Full textAbstract:
The best way to obtain significant results in science is to combine sophisticated experimental techniques and innovative samples. The aim of this thesis is to report an operative method to be used for the characterization of charge transfer phenomena in photo-active samples. This kind of analysis is extremely important for the doped TiO2 samples analyzed. These doped systems are promising photo-catalysts for hydrogen production from water splitting and pollutants degradation. Doping is an efficient method to decrease the energy needed to trigger the excitation of the photo-catalyst, otherwise possible only in the UV range. Identifying the role of dopants when the sample is excited is a mandatory step to understand the effects of dopants on the photo-catalytic properties of the systems. Both X-ray and optical techniques were used to characterize the samples and to follow those charge transfer phenomena induced by a visible excitation. Exploiting the unique characteristics of X Ray Absorption Fine Structure (XAFS) it was possible to determine the local structure of dopants inside the TiO2 matrix. With a differential illumination High Resolution Fluorescence Detected (HERFD) XAFS experiment an atomistic description of the light-induced charge transfer phenomena in V-doped TiO2 systems was obtained. The same physical process was also indirectly highlighted using optical ultrafast transient absorption spectroscopy. With this technique the inter-band transitions triggered by a visible light excitation were followed in real time. The combination of the two kinds of techniques made possible a complete description of the role of V dopants that, injecting charge carriers, lower the energy needed to trigger the photo-generation and surface trapping of charge carriers fundamental for the photo-catalytic processes.
37
Schonewille, Ronald Hiram. "Oxidation of copper-sulphur matte by submerged gas injection, mass transfer rates and physical phenomena." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ28054.pdf.
Full text
38
Zhou, Chunguang. "Gasification and Pyrolysis Characterization and Heat Transfer Phenomena During Thermal Conversion of Municipal Solid Waste." Doctoral thesis, KTH, Energi- och ugnsteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154587.
Full textAbstract:
The significant generation of municipal solid waste (MSW) has become a controversial global issue. Pyrolysis and gasification technologies for treating rejects from solid waste disposal sites (SWDSs), for which over 50 % of MSW is attributed to combustible species, have attracted considerable attention. MSW is an alternative energy source that can partly replace fossil resources; there is an increasing awareness that global warming caused by the utilization of fossil resources is occurring. The goal of this thesis is to realize the efficient and rational utilization of MSW and decrease the harmful impact of pollutants, such as dioxin, HCl, and CO2, on the environment. To achieve this goal, some fundamental studies have been experimentally and numerically conducted to enhance the understanding of the properties of municipal solid waste thermal conversion. In this thesis, the pyrolysis behaviors of single pelletized recovered fuel were tested. A detailed comparison of the pyrolysis behaviors of typical recovered solid waste and biomass particles was conducted. A swelling phenomenon with a swelling ratio of approximately 1.6 was observed on the surface of pelletized recovered fuels. Subsequently, a particle model was constructed to describe the thermal conversion process for large recovered fuel particles that are composed of a high fraction of polyethylene (PE) and a comparable low fraction of cardboard. The results indicate that an understanding of the heat transfer mechanism in highly porous and molten structures and the selection of a heat transfer model are crucial for accurate prediction of the conversion process. MSW pyrolysis is a promising method for producing liquid products. With the exception of lignocellulosic materials, such as printing paper and cardboard, PE, polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) are the six main polymers in domestic waste in Europe. Characterization studies of the products obtained from these individual components, such as PE, PET, PVC, printing paper, and cardboard, have been conducted on a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system and a fixed-bed reactor. The possible pathways for the formation of the main primary/secondary products in rapid and conventional pyrolysis were also discussed. MSW steam gasification with CaO was performed in a batch-type fixed-bed gasifier to examine the effect of CaO addition on the heat transfer properties, pollutant removal, and devolatilization and char gasification behaviors in the presence of steam. A new carbon capture and recycle (CCR) system combined with an integrated municipal solid waste system was proposed. The foundation of the system is the development of a novel method to remediate CO2 using a high-temperature process of reforming CH4 and/or O2 and/or H2O without catalysts. Thermodynamic and experimental studies were performed. High temperatures significantly promoted the multi-reforming process while preventing the problem of catalyst deactivation. Potential improvements in the efficiency of the novel technology can be achieved by optimizing the reforming reactants. Landfill gas (LFG) and fuel gas from bio-waste treatment contain a considerable fraction of CH4, which may be a source of CH4 for this process.QC20141028
39
Donato, Adam Armido. "Multiscale Modeling and Uncertainty Quantification of Multiphase Flow and Mass Transfer Processes." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51246.
Full textAbstract:
Most engineering systems have some degree of uncertainty in their input and operating parameters. The interaction of these parameters leads to the uncertain nature of the system performance and outputs. In order to quantify this uncertainty in a computational model, it is necessary to include the full range of uncertainty in the model. Currently, there are two major technical barriers to achieving this: (1) in many situations -particularly those involving multiscale phenomena-the stochastic nature of input parameters is not well defined, and is usually approximated by limited experimental data or heuristics; (2) incorporating the full range of uncertainty across all uncertain input and operating parameters via conventional techniques often results in an inordinate number of computational scenarios to be performed, thereby limiting uncertainty analysis to simple or approximate computational models.
This first objective is addressed through combining molecular and macroscale modeling where the molecular modeling is used to quantify the stochastic distribution of parameters that are typically approximated. Specifically, an adsorption separation process is used to demonstrate this computational technique. In this demonstration, stochastic molecular modeling results are validated against a diverse range of experimental data sets. The stochastic molecular-level results are then shown to have a significant role on the macro-scale performance of adsorption systems.
The second portion of this research is focused on reducing the computational burden of performing an uncertainty analysis on practical engineering systems. The state of the art for uncertainty analysis relies on the construction of a meta-model (also known as a surrogate model or reduced order model) which can then be sampled stochastically at a relatively minimal computational burden. Unfortunately these meta-models can be very computationally expensive to construct, and the complexity of construction can scale exponentially with the number of relevant uncertain input parameters. In an effort to dramatically reduce this effort, a novel methodology "QUICKER (Quantifying Uncertainty In Computational Knowledge Engineering Rapidly)" has been developed. Instead of building a meta-model, QUICKER focuses exclusively on the output distributions, which are always one-dimensional. By focusing on one-dimensional distributions instead of the multiple dimensions analyzed via meta-models, QUICKER is able to handle systems with far more uncertain inputs.Ph. D.
40
Svenkeson, Adam. "How Cooperative Systems Respond to External Forces." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500014/.
Full textAbstract:
Cooperative interactions permeate through nature, bringing about emergent behavior and complexity. Using a simple cooperative model, I illustrate the mean field dynamics that occur at the critical point of a second order phase transition in the framework of Langevin equations. Through this formalism I discuss the response, both linear and nonlinear, to external forces. Emphasis is placed on how information is transferred from one individual to another in order to facilitate the collective response of the cooperative network to a localized perturbation. The results are relevant to a wide variety of systems, ranging from nematic liquid crystals, to flocks and swarms, social groups, and neural networks.
41
Michaïe, Sandra. "Experimental study of the fundamental phenomena involved in pool boiling at low pressure." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI040/document.
Full textAbstract:
L’ébullition est un mode de transfert de chaleur intervenant dans de nombreux systèmes thermiques ou énergétiques de par son efficacité. Dans certains, elle se produit à basse pression. La pression statique induite par la colonne de liquide au-dessus de la surface de formation des bulles n’est alors pas négligeable devant la pression de saturation à la surface libre. Dès lors, la pression et le sous-refroidissement induit ne peuvent plus être considérés homogènes autour des bulles, d’où des inhomogénéités des propriétés thermophysiques dans le fluide. Les influences relatives des forces s’exerçant sur une bulle pendant sa croissance sont modifiées par rapport aux pressions plus élevées : une dynamique de bulles différente apparaît. Ces conditions particulières affectent également les transferts thermiques. L’influence de la pression sur l’ébullition en vase a été étudiée expérimentalement dans le régime de bulles isolées en site unique. L’eau a d’abord été testée sur une large gamme de pressions subatmosphériques. Quatre comportements de dynamique de bulles ont été identifiés d’après la visualisation par caméra rapide. Plusieurs paramètres de la dynamique ont été quantifiés grâce à un traitement d’images adapté appliqué aux vidéos. Pour généraliser le concept d’ébullition à « basse pression » et mieux en appréhender les phénomènes fondamentaux, de nouveaux essais ont été réalisés avec un second fluide, le cyclohexane, choisi pour sa similitude thermodynamique avec l’eau bouillant en deçà de la pression atmosphérique. La comparaison des comportements des deux fluides a permis d’identifier certains paramètres responsables des spécificités du phénomène. En outre, de nouvelles fonctionnalités sont apportées au dispositif expérimental pour – notamment – effectuer la mesure rapide du flux transféré sous la bulle pendant sa croissance, synchroniser ces mesures thermiques avec l’acquisition d’images et étudier des surfaces d’ébullition structurées. Les résultats obtenus sont encourageants pour l’analyse des comportements spécifiques de l’ébullition à basse pression et ses applicationsBoiling is an efficient heat transfer mode used in numerous thermal or energy systems. In some systems boiling takes place at low pressure. The static head of the liquid column over the wall where bubbles nucleate is then not negligible against the saturation pressure at the free surface level. The pressure and the induced subcooling degree therefore cannot be considered as homogeneous around growing bubbles, resulting in non-homogeneous thermophysical properties in the fluid. The relative influence of the forces acting on a growing bubble differs from higher pressure conditions, yielding specific bubble dynamics features. Heat transfer is consequently also affected. The effect of the pressure on pool boiling was experimentally investigated during the isolated bubbles regime taking place from a single activated nucleation site. Experiments were first conducted with water for a wide range of subatmospheric pressures. Four distinct bubble dynamics behaviors were identified through high-speed camera visualizations. An adapted image processing of the recordings enabled the measurement of several bubble dynamics characteristics. In order to generalize the concept of pool boiling at "low pressure" and to get a better understanding of the related fundamental phenomena, new experiments were performed with a second fluid, cyclohexane, chosen from original thermodynamic similarity with water boiling at pressures lower than atmospheric. The comparison of fluids’ behaviors made possible the identification of parameters governing the specific phenomena occurring during boiling at low pressure. Besides, the experimental facility was improved to provide new functionalities. The high-speed measurement of the heat flux transferred under the growing bubble, its synchronization with the high-speed videos images and the study of boiling on enhanced surfaces are in particular made possible. Results are encouraging for a better understanding of the specific behaviors of low pressure boiling and for its future implementation in practical applications
42
Schulz, Sebastian [Verfasser]. "Flow and heat transfer phenomena in a complex impingement system for integrally cooled turbine blades / Sebastian Schulz." München : Verlag Dr. Hut, 2018. http://d-nb.info/1155056094/34.
Full text
43
Karalis, Aristeidis 1978. "Novel photonic phenomena in nanostructured material systems with applications and mid-range efficient insensitive wireless energy-transfer." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44444.
Full textAbstract:
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 195-204).
A set of novel mechanisms for the manipulation of light in the nanoscale is provided. In the class of all-dielectric material systems, techniques for the suppression of radiative loss from incomplete-photonic-bandgap structures are developed: the cancellation of radiation channeled into discrete modes of the substrate, for resonant small-modal-volume cavities with patterned substrates, and the broadband mode-matching across the coupling interface, for large-bandwidth butt-coupled devices. Moreover, a hybrid plasmonic-dielectric material platform is introduced, able to localize light counter intuitively in low-index regions, by employing the unique subwavelength and cutoff properties of polaritonic waves, and to support dispersionless (to unusually-high orders) broadband-slow or stopped subwavelength light, by utilizing a simple planar multilayered dielectric structure. This platform can achieve a significant reduction in all (temporal, spatial and energy) light-scales and could enable compact and efficient optical buffers and active devices. A method for mid-range efficient and insensitive wireless energy-transfer is proposed. A condition of 'strong coupling' of resonances is identified as necessary and sufficient for efficient energy-exchange, and is shown to be satisfied at mid-range distances by carefully-designed high-Q subwavelength resonances of realistic systems both theoretically and experimentally, in the latter case by powering a 60W light-bulb wirelessly across a 2m-distance using two 60cm-diameter resonant objects and with 45% efficiency. A technique for further efficiency enhancement and radiation suppression is suggested, based on employing destructive interference between the coupled-objects' radiated far-fields. The scheme is also found fairly insensitive to the near-presence of extraneous objects, especially when utilizing the special class of magneto-quasi-static resonances.
(cont.) Applications of the proposed wireless-powering method can be found in both the macro- and micro-worlds, and range among industrial, technological, medical, consumer and more.
by Aristeidis Karalis.
Sc.D.
44
URBANI, DANIELE. "Overcoming light and mass transfer phenomena in gas-liquid biphasic reactions: introduction of the aerosol methodological paradigm." Doctoral thesis, Università degli studi di Ferrara, 2022. http://hdl.handle.net/11392/2496482.
Full textAbstract:
Overcoming light and mass transfer phenomena in gas-liquid biphasic reactions: introduction of the aerosol methodological paradigm
Mass transfer phenomena are a limitation factor especially in gas-liquid organic chemistry reaction. This issue can be overcome by exploiting the huge increase of the surface to volume ratio when spraying the reaction solution. Each droplet generated this way will react as a single reactor.
In this thesis the selective photo-oxidation of organic sulfides to sulfoxides and the utilization of CO2 for the synthesis of cyclic carbonates from the corresponding epoxides are both widely studied.
A model reaction has been chosen for the study of the photochemical oxidation of a water soluble sulfide to the corresponding sulfoxide mediated by singlet oxygen:
For this reaction several setup were built with the aim of enhancing the final conversion and the mass recovery of the process. A photochemical aerosol reactor was design and built in collaboration with the University of KULeuven to obtain allowing us to reach 95% conversion and complete selectivity toward the sulfoxide. The acceleration factor of the reaction kinetic is 144 compared to the bulk reaction.
The scope expansion of the model reaction towards organic sulfides that are not soluble in water was then carried on to place the foundation for further aerosol experiments. In this case a water:ethanol mixture is choose as green solvent for safety and environmental issues.
Severe climate change represents a threat for human life, and its effects on environment, economic and social development is widely studied. Unequivocally scientific evidences link climate change to greenhouse gases emissions, and identify CO2 as a greenhouse gas.
For this reason we thought of using CO2 as a reactive-carrier gas to carry out the synthesis of styrene carbonate from styrene oxide:
This synthesis was identified as the model reaction for further studies.
Without any previous experience in this field an extensive study of the scientific literature was done with the aim of identifying the best catalyst suitable for an aerosol reactor. KI/tetraethylene glycol is choose as catalyst for the comparison between bulk and aerosol reaction due to its features.
The kinetic study at different temperature of the model reaction in bulk and aerosol batch condition was carried on giving an acceleration factor up to 1,85. Unfortunately it was impossible during the PhD period to work with an aerosol flow reactor for CO2 reaction due to inadequate reactor setup and low reactivity of the gas.
For this purpose a modular aerosol reactor has been design and built to being able, in the forthcoming future, to fully exploit microdroplets environment:
Even if several data were collected with extreme difficulties, due to the novel approach choose on CCU technologies, those were sufficient to obtain a partnership for a NATO project call TANGO. The research group will now focus on the synthesis of new catalysts supported on magnetic nanoparticles that, hopefully, can convert styrene oxide into styrene carbonate with high yield and faster reaction time. All the experiments necessary are going to be exploiting the modular reactor designed and built with the experience gained on the strictly homogeneous reaction. The model reaction reported in this thesis will be the benchmark for future reactions.I fenomeni di trasferimento di massa sono un fattore limitante soprattutto nelle reazioni di chimica organica gas-liquido. Questo problema può essere superato sfruttando l'enorme aumento del rapporto superficie-volume quando si nebulizza una soluzione. Ogni goccia generata in questo modo reagirà come un singolo reattore. In questa tesi sono ampiamente studiate sia la foto-ossidazione selettiva di solfuri organici a solfossidi, sia l'utilizzo di CO2 per la sintesi di carbonati ciclici partendo dai corrispondenti epossidi. Una reazione modello è stata scelta per lo studio dell'ossidazione fotochimica di un solfuro solubile in acqua al corrispondente solfossido mediata dall’ ossigeno di singoletto: Per questa reazione sono stati costruiti diversi setup strumentali con l'obiettivo di migliorare la conversione finale e il recupero di massa del processo. Un reattore aerosol fotochimico è stato quindi progettato e costruito in collaborazione con l'Università di KULeuven, permettendo di raggiungere il 95% di conversione finale e la completa selettività verso il solfossido. Il fattore di accelerazione della cinetica di reazione è 144 rispetto alle condizioni di reazione classica. L'espansione metodologica della reazione modello verso solfuri organici non solubili in acqua è stata poi portata avanti in condizioni bulk ponendo le basi per ulteriori esperimenti in aerosol. In questo caso una miscela acqua:etanolo è stata scelta come solvente verde per questioni di sicurezza e sostenibilità ambientale. I cambiamenti climatici rappresentano una minaccia per la vita umana, e i loro effetti sull'ambiente e sullo sviluppo economico e sociale sono ampiamente studiati. Evidenze scientifiche inequivocabili collegano il cambiamento climatico alle emissioni di gas a effetto serra ed identificano la CO2 come uno di questi gas. Per questo motivo si è pensato di utilizzare la CO2 come gas reattivo nella sintesi dello stirene carbonato partendo dallo stirene ossido: Questa sintesi è stata identificata come la reazione modello per studi futuri. Senza alcuna esperienza precedente in questo campo è stato necessario effettuare un ampio studio della letteratura scientifica con l'obiettivo di identificare il miglior catalizzatore adatto ad un reattore aerosol. Il complesso KI/tetraetilen glicole è stato scelto come catalizzatore per il confronto tra la reazione bulk e quella aerosol per le sue caratteristiche, ideali per questa tipologia di sintesi. Lo studio cinetico a diverse temperature della reazione modello in condizioni di bulk e aerosol ha permesso di ottenere fattori di accelerazione fino a 1,85. Sfortunatamente non è stato possibile, durante il periodo di dottorato, lavorare con un reattore a flusso di aerosol per la reazione con la CO2 a causa della configurazione inadeguata dei reattori a disposizione e alla bassa reattività del gas. Per ovviare a questa mancanza è stato progettato e costruito un reattore aerosol modulare potenzialmente in grado, nel prossimo futuro, di sfruttare pienamente i vantaggi dell'aerosol: Nonostante la difficile raccolta dati, dettata del nuovo approccio scelto sulle tecnologie CCU, i risultati raggiunti sono stati sufficienti per ottenere un partenariato in un progetto NATO chiamato TANGO. Il gruppo di ricerca si concentrerà quindi sulla sintesi di nuovi catalizzatori supportati su nanoparticelle magnetiche che, si spera, possano convertire lo stirene ossido in stirene carbonato con un alta resa e tempi di reazione più rapidi. Tutti gli esperimenti necessari andranno a sfruttare il reattore modulare recentemente progettato e costruito a partire dall'esperienza maturata sulla reazione modello. La reazione modello riportata in questa tesi sarà anche il benchmark per le reazioni future.
45
CARDELLINI, ANNALISA. "Modelling of Multi-Scale Phenomena in Nanoparticle Suspensions." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2687171.
Full textAbstract:
Self- or driven-assembly of nanoparticles (NPs) into mesoscopic ordered structures play a crucial role in a large variety of applications including energy, pharmaceutical,
food, drug delivery, immunology and technological. On the one hand, trying to prevent and avoid the self-organization of nanoparticles has traditionally been the main issue to stabilizing nanosuspensions, foams, and emulsions. On the other hand, the aggregation of building-blocks into mesoscopic structures has allowed to explore new materials with desired functionalities and properties. In the latter context, a proper attention has been devoted to the dominant role of aggregation in altering the thermal properties of nanosuspensions. However, due to the challenges of controlling the inter-particle interactions and the process of aggregation, clear guidelines for a rational design of tailored suspensions is still missing. Accurately modelling heat and mass transport phenomena across many different length scales is essential to optimize the self-assembly and stability of colloidal suspensions. In this thesis, Molecular Dynamics (MD) simulations, Coarse-Grained (CG) techniques, Brownian Dynamics (BD) and theoretical modelling studies are combined to understand how the interfacial phenomena influence the mechanisms of building-block interactions and hence how to predict the shapes of assembled clusters and their related macroscopic properties. First, the behaviour of nanoconfined water and the adsorption of ionic surfactants at the solid-liquid nanoscale interface are investigated. Second, atomistic Potentials of Mean Force (PMFs) are evaluated between couples of NPs dispersed in aqueous solutions. A sensitivity analysis is carried out by altering the hydrophilicity of the nanoparticles, their surface charge and the salt concentration of the bulk solution. Moreover, the role of anionic (Sodium Dodecyl Sulphate -SDS-) and
cationic (Dodecyl Trimethyl Ammonium -DTAB-) surfactants is included in the evaluation of the PMF. All the study cases are then compared with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and remarkable discrepancies have emerged, underling the limits of a continuum theory to model the colloidal interactions at the nanoscale. In particular, the results highlight that the assumption of a uniform and continuum media and the hypothesis of homogeneous particles present in the DLVO theory break down at the solid-liquid nanoscale interface and by considering patchy NPs after surfactant adsorption. Thus, MD simulations offer the best alternatives to capture all coupled phenomena included in NP interactions. Subsequently, the atomistic PMFs are implemented in a multi-scale model, where MD simulations and Brownian dynamics are integrated offering a detailed picture of the kinetic of NP aggregation. The qualitative agreement with the experimental observations validates the novel multi-scale platform, able to connect the nanoscale features to the size of aggregates and related macroscopic properties of colloidal suspensions. Finally, with a coarse-grained technique, a force field for heterogeneous
NPs is also provided. Thus, in the present work, powerful tools and multi-scale modelling approaches are developed to describe some of the multi-scale phenomena
occurring in NP suspensions. Clear guidelines to perform multi-scale simulations of the self-assembly processes are proposed, and the first step towards a rational design
of NP suspensions is presented.
46
Paquet, Emil Friedrich. "Establishing a facility to measure the efficiency of structured packing under total reflux." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6834.
Full textAbstract:
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: Structured packing is often the preferred choice for column internals because of its low pressure drop and high efficiencies compared to that of trays and random packing. However, the mass transfer phenomena in these gas-liquid contacting devices is still not well understood, even though it is widely used in industry. A contributing factor to this is the lack of understanding and availability of experimental data in the open literature. These shortcomings complicate the design of a distillation column and make practical experience essential. There is thus a need for more experimental data, especially for packings where only limited information is available. The focus of this study was to establish a testing facility that can be used to measure the efficiency of structured packing under total reflux, and not to measure vast quantities of experimental data; the latter will be done in future. The facilities available at Stellenbosch University limited the internal diameter of the column to 0.2 m, which is sufficient to test higher surface area structured packings (≥350 m2/m3). The column is used with a thermosyphon reboiler that uses steam as the heating source and is equipped with a total condenser. Two sections are used for the packed bed that allow for a total packed height of 3.78 m (2x1.89 m). The column is set up to operate under total reflux and was designed to operate at pressures ranging from 0.3 to 1 bar abs, vapour flow rates of 0.73 – 3.65 (m/s) (kg/m3)0.5 and liquid flow rates of 5 – 25 m3/(m2.h). It was found that the 2-butanol/iso-butanol and the p-xylene/o-xylene systems are suitable test mixtures for this pilot plant setup. The VLE data from Kutsarov et al. (1993) and Zong et al. (1983) for p-xylene/o-xylene and 2-butanol/iso-butanol are thermodynamic consistent and was validated by VLE experiments done in this study. It was found that the experimentally obtained efficiency (HETP) and pressure drop data for Mellapak 350Y compared well with published results of Spiegel and Meier (1987). With regard to the predictive models, it was found that i) the SRP model predicted the HETP of Mellapak 350Y structured packing accurately in the pre-loading region and slightly over predicted the HETP in the loading region, whereas ii) the Delft model over predicted HETP and iii) the Billet and Schultes model under-predicted HETP under the entire tested range (i.e. over-predict efficiency). With regard to the pressure drop data i) the Billet model iv accurately predicted the pressure drop over the entire tested range, whereas ii) the SRP model accurately predicted the pressure drop in the pre-loading region and slightly over predicted the pressure drop in the loading region and iii) the Delft model over predicted the pressure drop over the entire range and followed an almost parallel trend to the results from the SRP model. It was also found that information in the field of mass transfer in a packed column is far from saturated, and there is a need for more experimental data and better understanding of the mass transfer phenomena in packed columns.
AFRIKAANSE OPSOMMING: Gestruktureerde pakking het ʼn laer drukval en ʼn hoër effektiwiteit in vergelyking met willekeurige pakkings en plate, en is daarom dikwels die voorkeur keuse vir pakkings materiaal in ʼn distilleer kolom. Die massa-oordrags verskynsels in hierdie gas-vloeistof kontaktors word egter nog nie goed verstaan nie, ten spyte van die grootskaalse aanwending in die nywerheid. ʼn Bydraende faktor is die tekort aan eksperimentele data in die ope literatuur. Die tekortkomings bemoeilik die ontwerp van distilleerkolomme en maak praktiese ervaring ʼn noodsaaklike vereiste. Daar is dus ʼn behoefte aan meer eksperimentele data veral vir pakkings waar daar min of geen data beskikbaar is nie. Die fokus van die studie was om ʼn toetsfasiliteit op te rig wat gebruik kan word om die effektiwiteit van gestruktureerde pakking onder totale terugvloei kondisies te bepaal, en dus nie om ‘n groot hoeveelheid data te genereer nie; laasgenoemde sal wel deel uitmaak van toekomstige studies. Die fasiliteite beskikbaar by die Universiteit van Stellenbosch het die binne diameter van die kolom beperk tot 0.2 m. Die diameter is voldoende om gestruktureerde pakkings met ʼn hoë oppervlakarea te toets byvoorbeeld pakkings met areas 350 m2/m3 en hoër. Die kolom gebruik ‘n verdamper (met stoom as energie bron) om die vloeistof te verdamp en ‘n totale kondensator (verkoel met verkoelingswater) om die damp te laat kondenseer. Twee seksies van 1.89 m elk word gebruik vir die gepakte bed en die kolom het dus ‘n totale pakkingshoogte van 3.78 m. Die kolom is opgestel vir totale terugvloei en is ontwerp om bedryf te word by drukke tussen 0.3 en 1 bar abs, damp snelhede van 0.73 tot 3.65 (m/s) (kg/m3)0.5 en vloeistof vloeitempo’s tussen 5 en 25 m3/(m2.h). 2-butanol/iso-butanol en p-xylene/o-xylene is gevind om geskik te wees as mengsels vir die toetsopstelling. Die damp-vloeistof fase-ewewig data van Kutsarov et al. (1993) en Zong et al. (1983) vir p-xylene/o-xylene and 2-butanol/iso-butanol is termodinamies konsistent en is gevalideer deur damp-vloeistof fase ewewig toetse in die studie. Daar is gevind dat die eksperimenteel bepaalde effektiwiteit en drukval data vir Mellapak 350Y pakking goed vergelyk met gepubliseerde data van Spiegel and Meier (1987). Die eksperimenteel bepaalde effektiwiteit data is met waardes van beskikbare modelle model vergelyk en daar is gevind dat: i) die SRP voorspel die effektiwiteit van Mellapak 350Y pakking akkuraat in die ‘pre-loading’ gebied maar toon afwykings van die eksperimentele data in die ‘loading’ gebied, ii) die Delft model voorspel ‘n hoër hoogte ekwivalent aan ‘n teoreties plaat (HETP) oor die hele gebied terwyl iii) die Billet en Schultes model weer ‘n laer HETP voorspel oor die hele gebied. Met betrekking toe die drukval data i) voorspel die Billet model die drukval akkuraat oor die hele gebied, ii) die SRP model voorspel die drukval korrek in die ‘pre-loading’ gebied maar begin afwyk van die eksperimentele data in die ‘loading’ gebied en iii) die Delft model voorspel groter waardes vir drukval oor die hele gebied en volg amper ʼn parallelle tendens met die SRP model. In die studie is daar gevind dat daarin die gebied van massa-oordrag nog ʼn tekort is aan eksperimentele data en daar baie navorsings geleenthede is.
47
Wang, Xiaohua. "Characterization of Mesoscopic Fluid-like Films with the Novel Shear-force/Acoustic Microscopy." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/736.
Full textAbstract:
The shear force mechanism has been utilized as a distance regulation method in scanning probe microscopes. However, the origin of shear force is still unclear. One of the most important reasons for the shear-force damping is due to the presence of a water contamination layer at the sample surface in ambient conditions. Understanding the behavior of such mesoscopic fluid-like films is of significance for studies of not only scanning probe microscopy but also other complex surface phenomena, such as nanotribology, lubrication, adhesion, wetting, and the microfluidity of biological membranes. This thesis investigates, in particular, the dynamics of mesoscopic fluids confined between two sliding solid boundaries. When fluids are constrained to nanometer-sized regions, their physical properties can greatly differ from those displayed by bulk liquids. To gain an insight into the fundamental characteristics of the confined fluid films, we exploit the versatile capabilities of the novel shear-force/acoustic near-field microscope (SANM), which is able to concurrently and independently monitor the effects of the fluid-mediated interactions acting on both the microscope's probe and the sample to be analyzed. Two signals are monitored simultaneously during each experimental cycle: the tuning fork signal, which is the oscillation amplitude of the probe and gives access to the shear force; and acoustic signal, which is detected by an acoustic sensor placed under the sample. Systematic experiments are carried out to investigate the effects of probe geometry, environmental humidity, and chemical properties of probe and sample surface (water affinity: hydrophobicity or hydrophilicity) on the probe-sample interactions, expressing the influence of the fluid-like contamination films.
48
Shi, Lei. "Application of Laser-Based Instrumentation to Study Fluid Flow and Heat Transfer Phenomena in Standing-Wave Thermoacoustic Devices." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521787.
Full text
49
Guardo, Zabaleta Alfredo. "Computational Fluid Dynamics Studies in Heat and Mass Transfer Phenomena in Packed Bed Extraction and Reaction Equipment: Special Attention to Supercritical Fluids Technology." Doctoral thesis, Universitat Politècnica de Catalunya, 2007. http://hdl.handle.net/10803/6455.
Full textAbstract:
El entendimiento de los fenómenos de transferencia de calor y de masa en medios porosos implica el estudio de modelos de transporte de fluidos en la fracción vacía del medio; este hecho es de fundamental importancia en muchos sistemas de Ingeniería Química, tal como en procesos de extracción o en reactores catalíticos. Los estudios de flujo realizados hasta ahora (teóricos y experimentales) usualmente tratan al medio poroso como un medio efectivo y homogéneo, y toman como válidas las propiedades medias del fluido. Este tipo de aproximación no tiene en cuenta la complejidad del flujo a través del espacio vacío del medio poroso, reduciendo la descripción del problema a promedios macroscópicos y propiedades efectivas. Sin embargo, estos detalles de los procesos locales de flujo pueden llegar a ser factores importantes que influencien el comportamiento de un proceso físico determinado que ocurre dentro del sistema, y son cruciales para entender el mecanismo detallado de, por ejemplo, fenómenos como la dispersión de calor, la dispersión de masa o el transporte entre interfaces.La Dinámica de Fluidos Computacional (CFD) como herramienta de modelado numérico permite obtener una visión mas aproximada y realista de los fenómenos de flujo de fluidos y los mecanismos de transferencia de calor y masa en lechos empacados, a través de la resolución de las ecuaciones de Navier - Stokes acopladas con los balances de materia y energía y con un modelo de turbulencia si es necesario. De esta forma, esta herramienta permite obtener los valores medios y/o fluctuantes de variables como la velocidad del fluido, la temperatura o la concentración de una especie en cualquier punto de la geometría del lecho empacado.
El objetivo de este proyecto es el de utilizar programas comerciales de simulación CFD para resolver el flujo de fluidos y la transferencia de calor y de masa en modelos bi/tri dimensionales de lechos empacados, desarrollando una estrategia de modelado aplicable al diseño de equipos para procesos de extracción o de reacción catalítica. Como referencia se tomaran procesos de tecnología supercrítica debido a la complejidad de los fenómenos de transporte involucrados en estas condiciones, así como a la disponibilidad de datos experimentales obtenidos previamente en nuestro grupo de investigación. Estos datos experimentales se utilizan como herramienta de validación de los modelos numéricos generados, y de las estrategias de simulación adoptadas y realizadas durante el desarrollo de este proyecto.
An understanding of the heat and mass transfer phenomena in a porous media implies the study of the fluid transport model within the void space; this fact is of fundamental importance to many chemical engineering systems such as packed bed extraction or catalytic reaction equipment. Experimental and theoretical studies of flow through such systems often treat the porous medium as an effectively homogeneous system and concentrate on the bulk properties of the flow. Such an approach neglects completely the complexities of the flow within the void space of the porous medium, reducing the description of the problem to macroscopic average or effective quantities. The details of this local flow process may, however, be the most important factor influencing the behavior of a given physical process occurring within the system, and are crucial to understanding the detailed mechanisms of, for example, heat and mass dispersion and interface transport.
Computational Fluid Dynamics as a simulation tool allows obtaining a more approached view of the fluid flow and heat and mass transfer mechanisms in fixed bed equipment, through the resolution of 3D Reynolds averaged transport equations, together with a turbulence model when needed. In this way, this tool permit to obtain mean and fluctuating flow and temperature values in any point of the bed.
The goal of this project is to use commercial available CFD codes for solving fluid flow and heat and mass transfer phenomena in two and three dimensional models of packed beds, developing a modeling strategy applicable to the design of packed bed chemical reaction and extraction equipment. Supercritical extraction and supercritical catalytic reaction processes will be taken as reference processes due to the complexity of the transport phenomena involved within this processes, and to the availability of experimental data in this field, obtained in the supercritical fluids research group of this university. The experimental data priory obtained by our research group will be used as validation data for the numerical models and strategies dopted and followed during the developing of the project.
50
Rolon, Soto Juan Enrique. "Coherent Exciton Phenomena in Quantum Dot Molecules." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1314742055.
Full text