Incorporating insulation material with phase change materials (PCMs) could help enhance the insulation capability for a refrigerator system. The phase change material can absorb or release large amount of latent heat of fusion depending on surrounding temperatures for efficient thermal management. This research focuses on how incorporating PCM to the conventional PU foam insulation affects the inside temperatures of the refrigerator system and in-turn helps in conserving energy by reducing the compressor run time. It was found that only 0.25-inch-thick PCM layer in insulation can certainly benefit the refrigerators by reducing the amount of electricity consumption and thus increasing the total energy savings through the numerical study results via COMSOL Multiphysics in this study. This work aims to investigate a PCM-incorporated insulation material to accomplish the enhancement of thermal insulation performance for refrigerators.

In this research work, an innovative method for measurement of thermal conductivity of a small volume of liquids, microsphere, and the single cancer cell is demonstrated using a micro-pipette thermal sensor (MPTS). The method is based on laser point heating thermometry (LPHT) and transient heat transfer. When a single pulse of a laser beam heats the sensor tip which is in contact with the surrounding liquids or microsphere/cells, the temperature change in the sensor is reliant on the thermal properties of the surrounding sample. We developed a model for numerical analysis of the temperature change using the finite element method (FEM) in COMSOL. Then we used MATLAB to fit the simulation result with experiment data by multi-parameter fitting technique to determine the thermal conductivity. To verify the accuracy in the measurement of the thermal conductivity by the MPTS method, a 10µl sample of de-ionized (DI) water, 50%, and 70% propylene glycol solution were measured with deviation less than 2% from reported data. Also, to demonstrate that the method can be employed to measure microparticles and a single spherical cell, we measured the thermal conductivity of poly-ethylene microspheres with a deviation of less than 1% from published data. We estimated the thermal conductivity of two types of cell culture growth media for the first time and determined the thermal conductivity of cancerous Jurkat Clone E6-1 to be 0.538 W/m.K ± 2%. Using the sensor of 1-2μm tip size, we demonstrated the MPTS technique as a highly accurate technique for determining the thermal conductivity of microfluidic samples, microparticles, biological fluids, and a non-invasive method for measuring the thermal conductivity of single cancer cell. This MPTS technique can be beneficial in developing a diagnosis method for the detection of cancer at an early stage. We also compared three effective thermal conductivity models for determining the weight percentage of Jurkat cell, considering water and protein as the major constituents. We discovered that a combination of Maxwell-Euken and effective medium theory model provides the closest approximation to published data and, therefore, recommend for the prediction of the cell composition.

Thermal cracking is an industrial process sensitive to both temperature and pressure operating conditions. The use of internally ribbed reactors is a passive method to enhance the chemical selectivity of the process, thanks to a significant increase of heat transfer. However, this method also induces an increase in pressure loss, which is damageable to the chemical yield and must be quantified. Because of the complexity of turbulence and chemical kinetics, and as detailed experimental measurements are difficult to conduct, the real advantage of such geometries in terms of selectivity is however poorly known and difficult to assess. This work aims both at evaluating the real benefits of internally ribbed reactors in terms of chemical yields and at proposing innovative and optimized reactor designs. This is made possible using the Large Eddy Simulation (LES) approach, which allows to study in detail the reactive flow inside several reactor geometries. The AVBP code, which solves the Navier-Stokes compressible equations for turbulent flows, is used in order to simulate thermal cracking thanks to a dedicated numerical methodology. In particular, the effect of pressure loss and heat transfer on chemical conversion is compared for both a smooth and a ribbed reactor in order to conclude about the impact of wall roughness in industrial operating conditions. An optimization methodology, based on series of LES and Gaussian process, is finally developed and an innovative reactor design for thermal cracking applications, which maximizes the chemical yield, is proposed

This work deals with the one-dimensional Stefan problem with a general time- dependent boundary condition at the fixed boundary. The solution will be obtained using a discrete random walk method and the results will be compared qualitatively with analytical- and finite difference method solutions. A critical part has been to model the moving boundary with the random walk method. The results show that the random walk method is competitive in relation to the finite difference method and has its advantages in generality and low effort to implement. The finite difference method has, on the other hand, higher accuracy for the same computational time with the here chosen step lengths. For the random walk method to increase the accuracy, longer execution times are required, but since the method is generally easily adapted for parallel computing, it is possible to speed up. Regarding applications for the Stefan problem, there are a large range of examples such as climate models, the diffusion of lithium-ions in lithium-ion batteries and modelling steam chambers for oil extraction using steam assisted gravity drainage.

<div>Two-phase flow and heat transfer has a wide variety of applications ranging from nuclear power plants to computer chip cooling. The efficient designs of these systems require a clear understanding of the mechanisms by which two-phase flows enhance heat transfer. With the rapid growth in computing power, Computational Fluid Dynamics is becoming an increasingly reliable predictive tool to understand the physics underlying two-phase flow and heat transfer. We identify the two chief phenomena</div><div>affecting heat transfer in two-phase flows as being the improved convective effect in bubbly flows, and the phase change phenomenon. We examine three key aspects of</div><div>bubbly flows in the present work namely: a) The flow of bubbles near vertical walls, b) the heat transfer associated with a non-condensable bubble rising near a vertical wall, and c) the heat transfer associated with boiling and condensation involving bubbles.</div><div><br></div><div>The first part involves studying the rise velocity of a layer of bubbles rising near a vertical wall. We derive a scaling between the rise velocity based Reynold’s number and the Archimedes number. The second part involves examining the flow pattern around a single bubble rising under the buoyancy effect in a shear flow near a heated wall, and how it affects the heat transfer from the wall. We study the dependence of the fractional improvement in Nusselt number at the wall on various non-dimensional parameters such as the Archimedes number, the Laplace number and the shear rate. Our study shows the existence of an optimum dimensionless shear rate for heat transfer enhancement and a strong dependence between the flow pattern around the bubble and its associated heat transfer enhancement. The third part involves building a numerical model to study flow boiling in micro-channels. We validate the proposed model with two benchmark problems and two experimental studies. The validated numerical tool is then used to understand the effect of varying the micro-channel inlet flow rate on its heat transfer characteristics. This numerical tool is further developed to include a stagnant micro-layer model that can simulate nucleate boiling. We then use it to study the flow boiling characteristics of a line of bubbles undergoing boiling and lift-off in a shear flow. In the end, based on existing literature in the field, we propose future tasks to be undertaken in the area of numerical two-phase flow.<br></div><div><br></div>

Le moteur électrique est l’un des organes principaux d’un véhicule électrique. Sa température, notamment celle des bobines, doit être réduite pour éviter toute dégradation. Le refroidissement par l’extérieur, comme avec une chemise d’eau dans le carter, apparait limité car les pertes générées dans les bobines doivent traverser des zones où la conduction thermique est très mauvaise. L’extraction des calories au cœur de la machine est préférable, mais les échanges thermiques avec l’air sont modérés. En application automobile, le moteur électrique est situé à proximité d’un circuit d’huile de lubrification. Le refroidissement par l'huile en contact direct avec les bobines est étudié.La thèse s’est d’abord attachée à la recherche bibliographique étendue sur les différentes solutions de refroidissement de moteur. Ensuite, les transferts thermiques à l’intérieur du moteur ont été modélisés par méthode nodale. A travers une étude de sensibilité, les principales améliorations thermiques passives ont été dégagées, puis les systèmes de refroidissement eux-mêmes ont été modélisés. Enfin, des essais ont été réalisés sur un banc spécialement conçu. Pour cette partie expérimentale, le refroidissement direct des bobines par circulation d’huile a été étudié en détail. Différents types d’injecteurs d’huile sur les têtes de bobine ont été testés dans diverses conditions de vitesse du rotor, température et débit d’huile.L’objectif de cette thèse est d’analyser l’ensemble des problématiques thermiques liées aux solutions de refroidissement à huile. Il s’agit d’une étude comparative de la performance des solutions à huile entre elles et avec celle d’un refroidissement à eau plus conventionnel. / Electric motor is one of the most important elements of an electric vehicle. Some elements, particularly the windings, can be affected by rising heat. External cooling, as water jacket in the case, appears to be limited because the losses generated in windings must pass through zones where conduction is very poor. Cooling in the core of the machine is preferable, but heat transfer with air is poor. Due to the presence of lubricating oil in the vicinity of the motor and the heat transfer enhancement that such a liquid provides, oil circulation on the windings has been considered.The research was first dedicated to an extensive bibliography on the different solutions of motor cooling. Then heat transfer within the motor was modelled by using the lumped system analysis. Thanks to a sensitivity analysis, the main parameters affecting temperature have been identified before cooling systems were modelled. Finally, tests were performed on a specially designed bench. Oil was introduced at each side of the machine to directly cool the stator coil end-windings. Several oil injection patterns were tested. The influence of the oil flow rate, rotation speed and oil temperature has been investigated.The objective of this PHD study is to analyse all the thermal issues related to the oil cooling systems. This is a comparative study of the performance of the oil cooling solutions. Comparison is also done with conventional water cooling.

[pt] Devido ao interesse crescente na utilização da energia solar no condicionamento de ar e secagem de alimentos, o presente trabalho descreve diversos ciclos solares de condicionamento de ar e apresenta um modelo de simulação das condições de operação e desempenho dos equipamentos usados num ciclo aberto de condicionamento. O modelo calcula o ciclo termodinâmico e especifica as características de transferência de calor e massa dos equipamentos para sistemas de qualquer capacidade térmica. Os resultados encontrados são exemplificados para sistemas de 1 a 5 toneladas de refrigeração de capacidade. / [en] Due to the increasing interest in the use of solar energy for air contioning and drying of foods, the present work describes different cycles of solar air conditioning and presents a model for simulating the operating conditions and the performance of the equipaments used in an open air conditioning cycle. The model calculates the termodynamic cycle and specifies the heat and mass transfer characteristics of the equipments for systems of any cooling capacity. The results are exemplified for systems of 1 to 5 refrigerating tons of cooling capacity.

Pour l’équipementier qui développe des roues et des freins d’aéronefs, le comportement thermique de l’équipement constitue un point de design majeur intervenant dans la conception. Cette discipline est aujourd’hui au centre des efforts de progression, car le concepteur est challengé sur la diminution de la masse du système. De ce fait, les limites en températures sont plus fréquemment atteintes, ce qu’il faut désormais anticiper dès l’appel d’offre pour éviter les itérations de conception. Cependant, les conditions dans lesquelles opère le système ainsi que son comportement thermique, sont mal connus et mal maîtrisés. Le caractère prédictif des simulations numériques faites pour dimensionner la structure, dépend directement de la précision du modèle et avec laquelle sont introduites, les conditions aux limites imposées en service à la structure.Aujourd’hui Safran ne dispose pas d’outil, ni de moyen suffisamment fiable pour prédire dès la phase de pré-dimensionnement, le comportement thermique de l’ensemble Roue & Frein. Il est connu que le design du frein et de la roue ont une influence réciproque sur la cinétique thermique de l’ensemble.Savoir prédire le comportement qualitatif du produit, en réponse aux sollicitations demandées par l’avionneur, permet de faire en amont des choix technologiques dont l’impact sur la thermique sera connu. Ainsi, la conception est dé-risquée d’éventuelles itérations de design pouvant retarder de plusieurs années la certification d’un avion.L’objet de cette thèse, est de proposer des solutions pour reproduire qualitativement la thermique Roue & Frein d’un avion, en prenant en compte des paramètres physiques associés aux solutions technologiques employées. Nous illustrons également que ces outils sont aussi un moyen de connaître les conditions dans lesquelles opère le système, lorsque l’on connaît à l’avance sa réponse en température en prenant le problème de manière inverse. / For the equipment manufacturer who develops aircraft wheels and brakes, the thermal behavior of the equipment refers to a major reference design point. This discipline is today at the center of concerns, because the designer is challenged on the system mass improvements. As a result, the temperature limits are more frequently reached, which must now be anticipated as early as possible.The pre-design phase should now also allow avoiding design iterations. However, the conditions under which the system operates and its thermal behavior, are poorly understood and poorly controlled. The predictive nature of the numerical simulations used to design the structure, depends directly on the model’s accuracy and on the in service boundary conditions imposed to the system.Today, Safran does not have any enough reliable tool or means to predict the thermal behavior of the Wheels & Brake assembly right from the pre-design phase. It is known that the design of the brake and the wheel have a reciprocal influence on the thermal kinetics of the system. Knowing how to predict the thermal behavior of the product, in response to stresses requested by the aircraft manufacturer, allows upstream technological choices whose impact on the thermal kinetics will be known. Thus, the design is disregarded of possible design iterations that could delay the aircraft certification by several years.The purpose of this thesis is to propose solutions to qualitatively reproduce the thermal behavior of an aircraft braking system, taking into account physical parameters associated with technological solutions. We also illustrate that these tools are also a way of knowing the conditions under which the system operates, when one knows in advance its temperature response by taking the problem in the opposite way.

O estudo consistiu em uma análise teórica experimental, com o desenvolvimento de uma correlação, dos parâmetros que afetam a ebulição nucleada de refrigerantes halogenados em superfícies cilíndricas lisas. Uma ampla análise da literatura permitiu levantar os distintos tópicos envolvendo este tema destacando entre eles o presente estudo. A análise da literatura envolveu, ainda, um estudo detalhado dos fundamentos da ebulição e das correlações para a previsão do coeficiente de transferência de calor. Foi projetado e construído um aparato experimental no qual foram realizados ensaios envolvendo superfícies de aço inoxidável, cobre e latão, os refrigerantes R-11, R-123, R-12, R-22 e R-134a, fluxos específicos de calor entre 0,8 e 120 kW/m&sup2, pressões reduzidas de 0,008 a 0,26 e rugosidade aritmética média variando entre 0,02 e 3,3 &#956m. A análise destes resultados possibilitou a verificação de comportamentos físicos inéditos segundo a literatura consultada. Destaca-se a análise de efeitos da condução longitudinal e da resistência térmica de contato entre a superfície de transferência de calor e os termopares. Esta análise foi incorporada ao procedimento de determinação da temperatura superficial, e permitiu estabelecer a distribuição de temperaturas ao longo do perímetro da superfície. Finalmente, com base no banco de dados levantado, foi desenvolvida uma correlação para o coeficiente de transferência de calor em ebulição nucleada plenamente desenvolvida de refrigerantes halogenados. / The present research has been focused in a theoretical and experimental analysis of the parameters that affect the pool boiling of halocarbon refrigerants in smooth cylindrical surfaces with the development of a correlation. A wide survey of the literature allowed to list the distinct topics related to this subject and to highlight among them the theme of this study. The literature analysis still involved a detailed study of the pool boiling fundamentals and of the correlations for the pool boiling heat transfer coefficient. An experimental set up has been developed and constructed in which were raise data involving surfaces of stainless steel, copper and brass, the refrigerants R-11, R-123, R-12, R-22 and R-134a, specific heat flux range of 0.8 to 120 kW/m&sup2, reduced pressures from 0.008 to 0.26 and arithmetic mean roughness varying between 0.02 and 3.3 &#956m. The analysis of these results revealed, according to the consulted literature, unpublished physical behaviors. In this work the effects of the longitudinal conduction and of the thermal contact resistance between the heat transfer surface and the thermocouple were analyzed carefully. This analysis was incorporated to the superficial temperature determination procedure and allowed to establish the temperature distribution along the surface perimeter. Finally, using the data base raised in this research, a simple and accurate correlation for the fully developed pool boiling heat transfer coefficient for halocarbon refrigerants applications has been developed.

A tecnologia de evaporação por filme descendente pode ser empregada em diferentes aplicações como processos químicos, petroquímicos, dessalinização de água, ciclos de refrigeração por absorção, OTEC Ocean termal energy conversion primer, só para mencionar alguns. No entanto, esta tecnologia tem demandado númerosos estudos devido a que ainda não é totalmente bem entendida, inclusive certos fenômenos básicos como são os problemas de distribuição do líquido, comportamento da espessura do filme e, sua transferência simultânea de calor e massa, sendo sujeito a vários estudos tanto numéricos quanto experimentais. Este trabalho foi focado no estudo da transferência simultânea de calor e massa, espessura do filme a os problemas de distribuição na vaporização de filme de água sobre tubos. Para isto, foi construída uma bancada de teste experimental, disponível para mensurar as seguintes variáveis; (a) temperatura da superfície dos tubos evaporadores, (b) espessura do filme descendente, (c) vazões mássicas, (d) potência elétrica fornecida aos tubos evaporadores, e (e) registro fotográfico infravermelho. O presente trabalho foi estruturado em dois aspectos principais; (1) avaliação do coeficiente de transferência de calor e massa, e (2) medição da espessura do filme descendente. Para os dois casos foram analisados os mecanismos de transferência de calor: sensível e latente. Para o primeiro ponto foram calculados os coeficientes local e médio de transferência de calor. No último ponto, usou-se um mecanismo formado por um micrômetro de elevada precisão aliado a um sistema elétrico para mensurar a espessura do filme líquido, sendo comparada com a teoria de Nusselt. Encontrou-se que há uma forte dependência da transferência de calor e massa com a espessura do filme descendente para a região laminar de Reynolds ente 160 a 950, implicando uma diminuição da taxa de transferência de calor com o aumento do Reynolds, já que a espessura de filme impôs uma maior resistência térmica. Além disso, avaliou-se o sistema de medição da espessura do filme com 25% de divergência da teórica de Nusselt. / Falling film evaporation technology can be used in different applications such as water desalination, refrigeration and ar-conditioning absorption cycles, OTEC (ocean thermal energy conversion primer), petrochemical and chemical process industries. This technology still demands númerous studies due to the lack of a complete understanding, even some basic phenomena such as the liquid distribution problem, liquid film thickness behavior and the heat and mass transfer coefficients are subject of intense experimental and numerical studies. This work has analyzed experimentally the heat and mass transfer coefficient, falling film thickness and the distribution system in water vaporization over tubes. For that, it was built an experimental setup, which has been measured the following; (a) tube wall temperature, (b) falling film thickness, (c) mass flow rate, (d) electrical power supplied to the evaporator tube, (e) infrared images. The present work has been structured in two mean aspects; (1) heat and mass transfer coefficient evaluation, and 2) falling film thickness measurement. In both topics, the two heat transfer mechanisms were analyzed: sensible and latent heat transfer. For the first topic, it has been analyzed the local and the overall heat transfer. For the second part, the method used a novel mechanical configuration (leverage effect), which improves the micrometer reading with more precision to obtain the film thickness, which was compared with the Nusselt theory. The experimental data showed that there is a strong dependence between the heat and mass transfer coefficient with the film thickness in the laminar region (Reynolds between 160 e 950), implying a decreasing of the heat transfer rate when the Reynolds increased, due to that the film thickness imposes a greater thermal resistance. Moreover, the study found the film thickness with a divergence of 25 % when it was compared with the theoretical Nusselt film thickness.