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Personne# Houxue Huang

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Transfert thermique

vignette|alt=Autour d'un feu, des mains reçoivent sa chaleur par rayonnement (sur le côté), par convection (au-dessus de ses flammes) et par conduction (à travers un ustensile en métal).|Les modes de

Heat flux

In physics and engineering, heat flux or thermal flux, sometimes also referred to as heat flux density, heat-flow density or heat flow rate intensity, is a flow of energy per unit area per unit time

Méthode expérimentale

Les méthodes expérimentales scientifiques consistent à tester la validité d'une hypothèse, en reproduisant un phénomène (souvent en laboratoire) et en faisant varier un paramètre. Le paramètre que l

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A key parameter in designing two-phase flow systems for the cooling of high heat flux electronics is the pressure drop in microchannel evaporators. As a result, an experimental study was performed to investigate the flow boiling pressure drop of refrigerants in two silicon multi-microchannel evaporators. Three types of refrigerants (R1233zd(E), R245fa and R236fa) were tested under three inlet subcoolings and three nominal outlet saturation temperatures. The test section's backside base temperatures were measured by an infrared (IR) camera. A single-phase flow validation in terms of the inlet and outlet restriction pressure drops and the channel flow friction factor was carefully done before the boiling tests. The operating conditions for stable flow boiling tests were: mass fluxes from 1250 to 2750 kg m(-2) S-1, heat fluxes from 20 to 64 W cm(-2). The resulted maximum vapor quality at the outlet manifold was 0.51. It is found that within the present test conditions the channel pressure drop increased with the inlet subcooling and inlet orifice width but slightly affected by the outlet saturation temperature. In addition, compared to the other two types of refrigerants, R236fa exhibited the lowest channel pressure drop due to its smallest liquid to vapor density ratio and liquid viscosity. Based on the obtained 184 points of stable flow boiling data, a new empirical model suitable for the high mass flux operating conditions was developed. The new pressure drop model yielded the best prediction of the experimental data with a mean absolute error (MAE) of 27.8% and it was thus implemented to predict the local pressure and temperature profiles, allowing a quantitative analysis to obtain highly accurate local heat transfer coefficients. (C) 2016 Elsevier Inc. All rights reserved.

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Measuring the strong local variation in heat transfer coefficients in multi-microchannel evaporators is related to the inverse heat conduction problem (IHCP). As the local flow heat transfer coefficients change greatly in magnitude from single-phase liquid at the entrance to a peak in slug flow and then to a minimum at the transition to the onset of annular flow and finally a new substantial rise up to the outlet, a significant heat spreading occurs due to the heat transfer process itself, and this has to be accounted for when processing the data. Until now, IHCP has not been introduced in the experimental study of heat transfer in such evaporators when reducing local experimental data. In this paper, a new method for processing experimental local heat transfer data by solving the 3D IHCP is proposed. This method is then applied and validated Using two sets of single-and two-phase flow experimental data obtained with infrared (IR) camera temperature measurements. The 14 400 raw pixel temperatures per image from the IR camera are first pre-processed by a filtering technique to remove the noise and then to smooth the data, where the IR camera has undergone a prior inhouse pixel by pixel insitu temperature calibration. Three filtering techniques (Wiener filter, spline smooth, and polynomial surface fitting) are compared. The polynomial surface fitting technique was shown to be more suitable for the current type of data set. Then the 3D IHCP is solved based on a finite volume method using the TDMA (Tridiagonal Matrix Algorithm) solver with a combination of Newton-Raphson iteration and a local energy balance method. Furthermore, the present 3D TDMA method (named as 3D TDMA) is compared with three other post processing methods currently used in the literature, among which the present one is found to be more accurate for reducing the local heat transfer data in multi-microchannel evaporators. (C) 2017 Elsevier Masson SAS. All rights reserved.

Houxue Huang, Nicolas Lamaison, John Richard Thome

Multi-microchannel evaporators are often used to cool down electronic devices subjected to continuous heat load variations. However, so far, rare studies have addressed the transient flow boiling local heat transfer data occurring in such applications. The present paper introduces and compares two different data reduction methods for transient flow boiling data in a multi-microchannel evaporator. A transient test of heat disturbance from 20 to 30W cm(-2) was conducted in a multi-microchannel evaporator using R236fa as the test fluid. The test section was 1 x 1 cm(2) in size and had 67 channels, each having a cross-sectional area of 100 x 100 mu m(2). The micro-evaporator backside temperature was obtained with a fine-resolution infrared (IR) camera. The first data reduction method ( referred to three-dimensional (3D)-TDMA) consists in solving a transient 3D inverse heat conduction problem by using a tridiagonal matrix algorithm ( TDMA), a Newton-Raphson iteration, and a local energy balance method. The second method ( referred to two-dimensional (2D)controlled) considers only 2D conduction in the substrate of the micro-evaporator and solves at each time step the well-posed 2D conduction problem using a semi-implicit solver. It is shown that the first method is more accurate, while the second one reduces significantly the computational time but led to an approximated solution. This is mainly due to the 2D assumption used in the second method without considering heat conduction in the widthwise direction of the micro-evaporator.