An experimental investigation was carried to examine the flow/ thermal field characteristics with/without phase change in the microchannels and compared with the traditional results. There are three parts in this study. The first part investigated the 2-D flow field measured by the micro particle image velocimetry (£gPIV) in a single PMMA microchannel fabricated by an ArF excimer laser. The slip boundary condition in the microchannel wall was also discussed. The second part studied the influence of surface condition (hydrophilic vs hydrophobic) on the flow/thermal field in a micro cooling device which included twenty parallel microchannels, which was fabricated by SU-8 microfabrication technique and replicated by the PDMS replica technique. The UV/ozone device was used to change the PDMS microchannels¡¦ surface condition from hydrophobic to hydrophilic and the £gPIV/£gLIF system was also used to measure the velocity and temperature distribution. The third part investigated the two-phase subcooled flow boiling phenomena (onset of nucleate boiling, boiling curve, flow patterns, bubble departure diameter and frequency) in the seventy-five parallel microchannels fabricated by SU-8 microfabrication technique, and aimed to raise the critical heat flux (CHF) and heat transfer coefficient to enhance the cooling efficiency. Three major methods were used in this study, as follows: (1) To add the cavity angle of £c = 60¢X, 90¢X, and 120¢X on the microchannel side walls. (2) To coat 2 £gm diamond film on the Cu heated surface. (3) To add 1 vol. % Multi-walled Carbon Nanotube (MCNT) into the working medium (deionized water). The goal of this paper is to develop a high heat flux cooling technique and apply the experimental results to solve the cooling problem resulting from the exceedingly high heat flux from the electronic component.

The aim of this study is to design and build a miniature spray cooling system, in which the manufactured and adopted chamber, pump and heat exchanger are smaller than the conventional ones. An experiment was conducted to explore the cooling performance of the spray cooling system after its size has been minimized. In the experiment, copper was used to make the heated surface and different working media, such as DI water, as nanofludics with silver and multi-walled carbon nanotubes powder were sprayed on the heated surface to enhance the heat dissipation efficiency of the system. The experiment in this study was set according to two conditions: transient and steady state, with Weber number as the main parameter, to observe the boiling phenomenon of different working media on heated surface and to record the temperature changes of the heated surface. The results were shown in boiling curve and cooling curve. The ultimate goal of this study was to obtain a better understanding of the cooling performance of the miniature spray cooling system in order to apply it to micro-electronic cooling devices, thereby solving the problem of the sharp increase in heating power per unit area on electronic components.

No description available.

L'objectif de cette thèse est d'étudier les différents régimes d'ébullition transitoires rencontrés lors de la mise en froid d'un tube chauffé par un écoulement interne de fluide. Le dispositif expérimental LORETA a été conçu pour réaliser des expériences au sol en écoulement vertical ascendant et en microgravité lors de vols paraboliques. L'effet du débit, de la température du liquide et du niveau de gravité dans les différents régimes d'ébullition a pu être clairement mis en évidence. Une dégradation des transferts thermiques en microgravité est observée, en particulier lors de l'ébullition en film. Une modélisation basée sur la résolution des équations du modèle à deux fluides permet la prédiction pour les deux niveaux de gravité. L'ensemble de la courbe d'ébullition a put être modélisée par des lois adaptées de la littérature. L'utilisation de ces lois pour des fluides cryogéniques semble raisonnable, au vu de la comparaison avec quelques données de la bibliographie. / The objective of this thesis is to study the boiling regimes encountered during the transient cooling of a heated tube by an internal fluid flow. The experimental apparatus LORETA was designed for experiments on ground in vertical upward flow and on microgravity during parabolic flights. The effect of flow rate, liquid temperature and level of gravity in different boiling regimes has been clearly shown. A decrease of heat transfer in microgravity is observed, especially during film boiling. Models based on solving equations of two-fluid model allow the prediction for the two levels of gravity. The entire boiling curve could be modeled by modified laws of literature. The use of these laws for cryogenic fluids seems reasonable, given the comparison with some data from the bibliography.

<p>In this study, universal databases and semi-empirical correlations are developed for cryogenic two-phase heat transfer and pressure drop in heated tubes undergoing flow boiling.</p>