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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

THE EFFECT OF HEATING DIRECTION ON FLOW BOILING HEAT TRANSFER OF R134A IN MICRO-CHANNELS

Xu Mingchen
Institute of Thermal Engineering, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China; Beijing Key Laboratory of Flow and Heat Transfer of Phase Changing in Micro and Small Scale, Beijing 100044, China

Jia Li
Institute of Thermal Engineering, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China; Beijing Key Laboratory of Flow and Heat Transfer of Phase Changing in Micro and Small Scale, Beijing 100044, China

Dang Chao
Institute of Thermal Engineering, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China; Beijing Key Laboratory of Flow and Heat Transfer of Phase Changing in Micro and Small Scale, Beijing 100044, China

Peng Qi
Institute of Thermal Engineering, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China; Beijing Key Laboratory of Flow and Heat Transfer of Phase Changing in Micro and Small Scale, Beijing 100044, China

Abstract

This paper presents effects of heating directions on heat transfer performance of R134a flow boiling in micro-channel heat sink. The heat sink has 30 parallel rectangular channels with cross-sectional dimensions of 500μm width, 500μm depth and 30mm length. The experimental operation condition ranges of the heat flux and the mass flux are 13.48 to 82.25 W/cm2 and 373.3 to 1244.4 kg/m2s respectively. The vapor quality range from 0.07 to 0.93. The heat transfer coefficients of top heating and bottom heating both are up to 25 kW/m2 K. Two dominate transfer mechanisms of nucleate boiling and convection boiling are observed according to boiling curves. The experimental results indicate that the heat transfer coefficient of bottom heating is 13.9% higher than that of top heating in low heat flux, while in high heat flux, the heat transfer coefficient of bottom heating is 9.9% higher than that of top heating because bubbles are harder to divorce the heating wall. And a modified correlation is provided to predict heat transfer of top heating.

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