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Flow Boiling Heat Transfer of Subcooled Water on Sintered Microporous Surfaces

[+] Author and Article Information
Yeonghwan Kim, Junsub Kim

Department of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, Korea

Seung M. You

Mechanical Engineering Department, University of Texas at Dallas, Richardson, USA

Jungho Lee

Department of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, Korea
jungho@kimm.re.kr

Jeong Lak Sohn

Extreme Mechanical Engineering Research Division, Korea Institute of Machinery and Materials, Daejeon, 34103, Korea

Jungho Lee

Extreme Mechanical Engineering Research Division, Korea Institute of Machinery and Materials, Daejeon, 34103, Korea
jungho@kimm.re.kr

J. Heat Transfer 139(8), 080906 (Jun 05, 2017) Paper No: HT-17-1181; doi: 10.1115/1.4036883 History: Received April 01, 2017; Revised April 28, 2017

Abstract

Electronic devices such as battery packs in electric vehicles and LED lights require advanced control in temperature uniformity for their optimum performance and prolonged lifetime. Flow boiling heat transfer of subcooled water (∆Tsub = 20K) in a 300 mm long minichannel with the cross section of 20×10 mm2 was investigated to improve the temperature uniformity over the entire minichannel. The minichannel was uniformity heated from the bottom copper surface. A 10 mm thick Pyrex glass was used for the top plate of the channel to visualize two-phase flow during the experiment. Microporous coating was fabricated by sintering copper particles on the top surface of the copper block. The average particle size was 50 μm, the average coating thickness was 300 μm, and the porosity was 41%, respectively. At the heat flux of 100 kW/m2, more bubbles are shown on the microporous surface compared with plain surface, resulting in better boiling heat transfer performance. These bubbles were large and stationary as liquid is evaporated and condensed to transport the heat as if heat pumps. As heat flux increases, bubble nucleation becomes more intensive, however, the larger stationary bubbles observed at 100 kW/m2 started to decrease. Most of the generated bubbles flowed through the downstream and they shrank quickly upon departure from the wall due to the 20K subcooling. High speed video showed some streaks of these small bubbles, and more streaks were observed as the heat flux increased. As shown in the left graph above, at 50 kW/m2 in subcooled flow boiling, both plain and microporous surfaces show similar local wall temperature because both are placed in the single-phase regime. In contrast, the difference of wall superheat between plain and porous surface is relatively large at higher heat flux of 500 kW/m2. Sintered microporous surface showed smaller increase in wall superheat compared with plain surface at higher wall superheat. [This study was supported by National Research Council of Science and Technology (NST) grant, Korea (Grant No. KIMM-NK203B)].

Copyright (c) 2017 by ASME
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