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Flow Visualization inside Thermosyphon for Measuring Heat Transfer Limit

[+] Author and Article Information
Jungho Lee

Department of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, 34103, Korea
jungho@kimm.re.kr

Jaebum Park

Department of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, 34103, Korea
johnpaulpark@snu.ac.kr

Jinsub Kim

Department of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, 34103, Korea
jskim129@kimm.re.kr

Seung M. You

Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
you@utdallas.edu

1Corresponding author.

J. Heat Transfer 139(2), 020911 (Jan 06, 2017) Paper No: HT-16-1724; doi: 10.1115/1.4035581 History: Received November 07, 2016; Revised November 13, 2016

Abstract

Heat pipe is a highly effective passive heat transfer device using phase change within small temperature difference. It is noted that heat pipe should be operated under heat transfer limit for practical heat pipe heat exchanger applications. The measurement in local and overall heat transfer coefficient is significant to anticipate the heat transfer limit. The wall temperatures and inner working fluid temperatures were measured to determine the heat transfer coefficient. The adiabatic part with transparent Pyrex glass was visualized to understand flow behaviors inside the thermosyphon. The dynamic behaviors of condensed working fluid were visualized for the specific tilted angle and power inputs at pseudo steady-state. At low heat input of 250W, the thin condensed liquid film is observed to be returned from condenser to evaporator. With increasing heat input of 500W, the nucleate boiling starts to occur in evaporator. More activated vapors turn to make wavy motion in free surface of the returned condensed liquid film which is thickened. In power input of 1,250W, the vigorous flow motion happens periodically and the interaction between vapor and liquid bursting reaches a maximum heat transfer which is led to the heat transfer limit in the thermosyphon. Over heat transfer limit (2,000 and 2,500W), the overall heat transfer is decreased when the degree of bursting motion between vapor and liquid is gradually reduced.

Copyright (c) 2017 by ASME
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