Système de refroidissement d'un récepteur de système photovoltaïque de haute concentration

International audienceLe système de refroidissement proposé pour traiter la problématique des hauts flux énergétiques des générateurs photovoltaïques de haute concentration combine les caractéristiques des jets impactants et des micro canaux. Ces deux technologies, actuellement utilisées dans le domaine de l'électronique de puissance, présentent un inconvénient pour leur application en concentration solaire : la non uniformité des températures dans le sens de l'écoulement qui provoque la diminution du rendement du récepteur photovoltaïque. Cette étude présente l'effet de la variation des paramètres caractéristiques des deux technologies combinées dans le système proposé sur l'uniformité des températures des cellules photovoltaïques

Experimental analysis of flow boiling pressure drop through copper metallic foam

This work concerns the flow boiling pressure drop inside a channel filled with metallic foam soldered to its lateral walls. Notice that Open cell metallic foams are increasingly used in the heat and mass exchangers. This is due to the considerable opportunity that this material could offer in terms of hydrodynamic characteristics namely porosity and permeability which are larger than 0.88 and 10-7 m2, respectively. The state of the art shows that the works in this field are still in their early stages. In this study the tested metallic foam is from copper with 97% porosity and 36 PPI (Pore per Inch Linear). The working fluid is n-pentane. The independent variables are: the mass flux in the range from 10 to 100 kg/m2s and heating power which varies between 0 and 25 W/cm2. The dependent variables are: the static pressure and exit quality. The hydrodynamics results represented in terms of pressure drop are qualitatively similar to those found for plain tube. The two-phase friction multiplier is used to compare results of the present work with those in the literature. Hence results are compared to correlations in the literature for metal porous media. As metallic foam occupies only 5% of the channel entire volume, the obtained results are also compared to those given by the homogeneous and separated models for two-phase flow in plain tube. The results concerning pressure drop through metallic foam found in this work are in good agreement with the homogeneous model with a discrepancy of about 25%, for the other models this discrepancy is upper to 50%

Boiling heat transfer inside parallel microchannels

Heat transfer study was carried out on convective boiling of R134a through nine horizontally positioned, parallel microchannels. The microchannels were of circular cross sections with internal diameter and length of 0.77 mm and 150 mm, respectively. The test conditions are as follows: mass velocity, G, of 250, 500, 750 and 1000 kg/m2s; inlet pressure, pin, of 600, 700, and 900 kPa and subcooling degrees of 1, 10 and 20oC. The experimental results for heat transfer coefficient are compared with seven correlations and semi-empirical models and the best predictions are obtained with the models of Sun and Mishima [13] and Thome et al. [15] for which the Mean Absolute Error was 14.4% and 14.9%, respectively.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

PREFACE: DROPS, BUBBLES, AND THIN FILMS, SPECIAL ISSUE HONORING PROFESSOR OLEG KABOV

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A review on boiling heat transfer enhancement with nanofluids

There has been increasing interest of late in nanofluid boiling and its use in heat transfer enhancement. This article covers recent advances in the last decade by researchers in both pool boiling and convective boiling applications, with nanofluids as the working fluid. The available data in the literature is reviewed in terms of enhancements, and degradations in the nucleate boiling heat transfer and critical heat flux. Conflicting data have been presented in the literature on the effect that nanofluids have on the boiling heat-transfer coefficient; however, almost all researchers have noted an enhancement in the critical heat flux during nanofluid boiling. Several researchers have observed nanoparticle deposition at the heater surface, which they have related back to the critical heat flux enhancement

Boiling Flow Pressure Drop Modeling In A Minichannel

The present paper deals with two-phase flow pressure drop modeling. This is based on solving the mass, momentum and energy balance equations in steady state conditions. In the two-phase zone, the liquid-vapor is assumed to be a homogeneous fluid. The calculated pressure drop variation is found to be similar to the experimental one when the two--phase flow is steady. In the unsteady state conditions characterized by high amplitude of the pressure fluctuations, the computed pressure drop is found to be different from the experimental mean pressure drop. This difference is all the higher as the pressure fluctuation is high