Abstract There are three focal points in this experimental study¡G(1)Change Reynolds number(Re) and measure the heat transfer coefficients on upper¡Bback¡Bside and front surfaces of a chip for standard height(20mm)¡F(2)Influences of the surface heat transfer coefficients when change the heights of a chip to 10mm and 30mm , then compare with the results of a chip with standard height¡F(3)Compare the heat transfer effects of a chip on different positions of the testing region. The range of Re is 2000~10000 in this experiment and the chip sets are installed on the testing board with a 3x4 array. According to similarity principles to setup whole experimental models¡Fassume this experimental system is a semi-infinite region and its heat transfer model is one dimension¡Fuse the transient heat transfer method with thermochromic liquid crystal as the surface thermometer , then we assemble micro video cameras in the experimental system to obtain the color changing images on chip surfaces. The software , LCIA (Liquid Crystal Image Analysis) , is used to analysis the changed color and the temporal history of the surface temperatures to determine the local heat transfer coefficients on chip surfaces. The results show¡G(1)The heat transfer coefficients on chip surfaces are increased with Re and effects of vortex¡F(2)Upper surface of the chip has the largest average heat transfer coefficient(h) , front surface and side surface have almost the same at lower Re , but at higher Re , of front surface is larger than side surface¡Fback surface has the lowest ¡F(3)When change the height of the first chip to 10mm , it has the best heat transfer effects at Re=2175 and 3257¡Fthere is almost the same effects at Re=4423 with different heights(10mm , 20mm and 30mm) and from Re=5535 to 9973 , this chip has the best heat transfer effects at 30mm. Then change the heights of the second and third chips , there are the best heat transfer effects at 30mm and the lowest at 10mm¡F(4)When fix heights of the chips at 10mm and 20mm , there are more better heat transfer effects as chips more close to the entrance of the testing channel , but once the heights of chips are 30mm , the positions of chips on the testing region are not very important influences to heat transfer effects.

Soot is formed whenever the combustion of hydrocarbon fuels is incomplete. Since soot particles are very small, they can be inhaled and cause severe health problems, such as pulmonary diseases. They can also cause environmental pollution, and have a significant effect on global warming and melting of polar ice sheets. The environmental and health impact of soot depends strongly on soot particle size and morphology, so there is a pressing need for measuring techniques that characterize aerosolized soot. Laser-Induced incandescence (LII) has proved to be a reliable technique for making spatial and temporal measurements of soot primary particle sizes and soot volume fractions. Nevertheless, there are some unresolved issues in LII, which may cause large errors in soot primary particle size inferred from LII data. One of these issues is anomalous cooling, which is the unexpectedly high initial rate of soot particle cooling observed in experiments, which can not be predicted by LII models. Among the speculations about the possible causes of this phenomenon is the transient gas dynamics effects which have been ignored in LII models. Another phenomena that has been speculated to affect LII predictions in high fluence LII, is how the gas dynamics of sublimed carbon clusters impact the local gas dynamics surrounding the particle during the cooling phase. The focus of this thesis is to investigate transient effects on heat conduction in low fluence LII, and the gas dynamics of sublimed species in high fluence LII using Direct Simulation Monte Carlo (DSMC) method. DSMC is a statistical/numerical method which works based on the physics of Boltzmann equation. In this method a large number of real molecules are represented by the so called simulated molecules and the state of these molecules is tracked during the simulation as they undergo collisions with each other and with the boundaries. The results show that transient effects contribute to anomalous cooling but are not the only cause of this phenomenon. The time scale over which transient effects are significant is also found to be very close to that of anomalous cooling which implies the real cause of anomalous cooling has some similarities to transient effects. Also regarding gas dynamics of sublimation, two effects in particular have been investigated using DSMC, namely, back flux of sublimed species and formation of shock waves. DSMC results confirm the back flux of sublimed species but no shock wave was observed for the boundary conditions considered in this study.

Thermosyphon transient operation was numerically modeled. The numerical model presented in this work overcame the limitations of previous studies by including transient conduction in the vessel wall, shear stress between the rising vapor and the falling film in the thermosyphon, the influence of the mass in the liquid pool in the evaporator, and by using a more refined and accurate numerical grid. Unique to this model was the accounting for temporal changes in the effective length of the vapor space due to the expanding and contracting of non-condensable gases in the vapor space. The model assumed quasi-steady one-dimensional vapor flow, transient one-dimensional flow in the falling liquid film, and transient behavior in the liquid pool in the evaporator. The model also assumed transient two-dimensional conduction in the thermosyphon wall. Using fundamental principles, the governing equations used in the numerical model were developed and then written in finite difference form. The finite difference forms of the governing equations were integrated using an explicit scheme. A sensitivity study was performed and found that the numerical model was accurate to 4%. An experiment was also conducted to validate the numerical model. The experiment used three distinct transient heat loads to simulate gradual, moderate and sharp increases in temperature. The uncertainty of the experiment was shown to be 2.3%. The temperatures from the numerical model were then compared to those measured during the physical experiment to determine the validity of the numerical model. The model was further exercised to develop a useful engineering relationship that can be used to predict the transient performance of a thermosyphon.

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.

In the present study, the local heat transfer coefficient over the surface of the tube row of a fin-and-tube heat exchanger is to measure. The test cases including the tube row arrangement of staggered and in-line, Reynolds number range of 2000 to 9000, and transverse tube pitch of S=2.0D, 2.5D and 2.8D, are studied and discussed. Experimental models of heat exchangers are constructed according to similarity principles. Complete distribution of local heat transfer coefficients are measured over the full surface of the tube row of a fin-and-tube heat exchanger by the transient heat transfer method with thermochromic liquid crystal used as the surface thermometer. And using micro video camera assembled in the experimental system to obtain the experimental image. Software, LCIA(Liquid Crystal Image Analysis), is used to obtain the temporal history of the surface temperature used to determined the local heat transfer coefficient. The results show that the heat transfer coefficient over the surface of the fin tube row increases with the Reynolds number. And the heat transfer coefficient for staggered cases is larger than that for in-line cases. The heat transfer coefficient on the surface of the tube row with transverse tube pitch S=2.0D is similar to the case with S=2.5D, and is larger than the case with S=2.8D. Therefore, there should exist an optimum geometry of the plate fin for a fin-and tube heat exchanger.

The extreme operating conditions in deepwater drilling lead to serious relative problems. The knowledge of subsea temperatures is of prime interest to petroleum engineers and geo-technologists alike. Petroleum engineers are interested in subsea temperatures to better understand geo-mechanisms; such as diagenesis of sediments, formation of hydrocarbons, genesis and emplacement of magmatic formation of mineral deposits, and crustal deformations. Petroleum engineers are interested in studies of subsurface heat flows. The knowledge of subsurface temperature to properly design the drilling and completion programs and to facilitate accurate log interpretation is necessary. For petroleum engineers, this knowledge is valuable in the proper exploitation of hydrocarbon resources. This research analyzed the thermal process in drilling or completion process. The research presented two analytical methods to determine temperature profile for onshore drilling and numerical methods for offshore drilling during circulating fluid down the drillstring and for the annulus. Finite difference discretization was also introduced to predict the temperature for steady-state in conventional riser drilling and riserless drilling. This research provided a powerful tool for the thermal analysis of wellbore and rheology design of fluid with Visual Basic and Matlab simulators.

Suite à un défaut de contrôle de la réaction nucléaire, un accident d’insertion de réactivité (RIA) peut survenir dans une centrale. Un pic de puissance se produit alors dans certains crayons de combustible, suffisamment important pour entraîner l’ébullition en film du réfrigérant qui les entoure. Ceci provoque la chute du refroidissement des crayons et donc une rapide et importante augmentation de la température de la gaine qui les entoure. L’évaluation du risque de rupture de la gaine est un sujet d’étude de l’Institut de Radioprotection et de Sûreté Nucléaire. Ces échanges de chaleur transitoires ne sont toujours pas compris et modélisés. Pour comprendre ces phénomènes, une boucle expérimentale a été construite à l’Institut de Mécanique des Fluides de Toulouse. Du HFE7000 circule de bas en haut dans une section d’essais verticale de géométrie semi-annulaire. Le demi-cylindre intérieur est une feuille de métal chauffée par effet Joule. Sa température est mesurée par une caméra infrarouge, couplée avec une caméra rapide pour la visualisation de l’écoulement. La courbe d’ébullition entière est étudiée en régimes stationnaire et transitoire : convection, déclenchement de l’ébullition, ébullition nucléée, passage en film, ébullition en film et remouillage. Les régimes stationnaires sont bien modélisés par des corrélations de la littérature. Différents modèles sont proposés pour représenter les transferts de chaleur transitoires : l’évolution de la convection et de l’ébullition nucléée se font de manière auto similaire pendant un palier de puissance. Ce constat permet de modéliser des évolutions plus compliquées telles des rampes de température. Le modèle de Hsu instationnaire prédit bien le déclenchement de l’ébullition. Pour des créneaux de puissance, le passage en film se fait à une température constante et le flux critique augmente avec la puissance, tandis que pour des rampes de puissance la température augmente mais le flux critique diminue avec l’augmentation de la puissance. Quand la paroi est chauffée, les flux de chaleur en ébullition en film sont beaucoup plus importants qu’en stationnaire mais ce régime est encore mal compris. Le refroidissement en ébullition en film et le remouillage sont bien caractérisés par un modèle à deux fluides. / A failure in the control system of the power of a nuclear reactor can lead to a Reactivity Initiated Accident in a nuclear power plant. Then, a power peak occurs in some fuel rods, high enough to lead to the coolant film boiling. It leads to an important increase of the temperature of the rod. The possible risk of the clad’s failure is a matter of interest for the Institut de Radioprotection et de Sûreté Nucléaire. The transient boiling heat transfer is not yet understood and modelled. An experimental set-up has been built at the Institut de Mécanique des Fluides de Toulouse (IMFT). Subcooled HFE-7000 flows vertically upward in a semi annulus test section. The inner half cylinder simulates the clad and is made of a stainless steel foil, heated by Joule effect. Its temperature is measured by an infrared camera, coupled with a high speed camera for the visualization of the flow topology. The whole boiling curve is studied in steady state and transient regimes: convection, onset of boiling, nucleate boiling, criticial heat flux, film boiling and rewetting. The steady state heat transfers are well modelled by literature correlations. Models are suggested for the transient heat flux: the convection and nucleate boiling evolutions are self-similar during a power step. This observation allows to model more complex evolutions, as temperature ramps. The transient Hsu model well represents the onset of nucleate boiling. When the intensity of the power step increases, the film boiling begins at the same temperature but with an increasing heat flux. For power ramps, the critical heat flux decreases while the corresponding temperature increases with the heating rate. When the wall is heated, the film boiling heat transfer is higher than in steady state but it is not understood. A two-fluid model well simulates the cooling film boiling and the rewetting.

Le mouvement d’humidité dans le réseau poreux de certains matériaux est très souvent à l’origine de phénomènes préjudiciables pour la durabilité des constructions du génie civil. C’est en particulier le cas pour le séchage du bois, générateur de fissures et de délaminations aux interfaces de collage, et pour le béton en situation d’incendie où le mouvement d’humidité peut induire des désordres irréversibles (écaillage). Le recours à des modèles prédictifs de ruine des structures nécessite donc la simulation du mouvement d’humidité au sein des matériaux. Ces modèles de transfert de masse et de chaleur sont sophistiqués et nécessitent d’être confrontés à des mesures afin d’être validés. Peu de techniques expérimentales existent pour mesurer les mouvements ou gradients d’humidité dans les réseaux poreux, en particulier en régime transitoire (séchage, incendie). Les techniques existantes sont de plus généralement coûteuses et imposent des conditions sévères de sécurité pour les chercheurs. L’objectif de la thèse est donc de mettre au point un dispositif de mesure de gradients d’humidité basé sur l’imagerie Térahertz. Il s’agit d’une technique de mesure relativement peu onéreuse et permettant de réaliser des mesures en régime transitoire. Un banc expérimental existant sera donc adapté à la mesure du champ d’humidité sur éprouvettes de bois en conditions thermo-hydriques variables, et sur éprouvettes de béton en situation de chauffage. Les résultats constitueront une base de données utile à la compréhension des phénomènes de dégradation des matériaux et seront directement utilisables comme outil de validation de modèles de calcul. / The movement of moisture in the porous network of certain materials is very often at the origin of phenomena prejudicial to the durability of the constructions of the civil engineering. This is particularly the case for the drying of wood, which creates cracks and delaminations at bonding interfaces, and for concrete in situations of fire where the movement of moisture can induce irreversible disorders (chipping). The use of predictive models of structural ruin therefore requires the simulation of the moisture movement within the materials. These mass and heat transfer models are sophisticated and need to be confronted with measurements in order to be validated. Few experimental techniques exist to measure moisture movements or gradients in porous networks, especially in transient conditions (drying, fire). Existing techniques are often expensive and impose severe conditions of safety for the researchers. The objective of the thesis is therefore to develop a device for measuring gradients of moisture based on Terahertz imagery. This is a comparatively inexpensive measuring technique and makes it possible to carry out transient measurements. An existing experimental bench will therefore be adapted to the measurement of the moisture field on wood specimens under variable water-moisture conditions and on concrete specimens in a heating situation. The results will constitute a database useful for understanding the phenomena of degradation of materials and will be directly usable as a validation tool for calculation models.