Technical Briefs

Experimental Study of a Two-Phase Thermosyphon With Porous Graphite Foam Insert

[+] Author and Article Information
L. W. Jin, I. Pranoto, H. Y. Li

School of Mechanical and Aerospace Engineering,  Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore

K. C. Leong1

School of Mechanical and Aerospace Engineering,  Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singaporemkcleong@ntu.edu.sg

J. C. Chai

 Mechanical Engineering Department, The Petroleum Institute, Abu Dhabi, United Arab Emirates


Corresponding author.

J. Thermal Sci. Eng. Appl 3(2), 024502 (Jul 05, 2011) (6 pages) doi:10.1115/1.4003885 History: Received October 27, 2010; Revised March 29, 2011; Published July 05, 2011; Online July 05, 2011

This paper presents an experimental study of heat transfer in a pool boiling evaporator with porous insert. Porous graphite foams were structured into cubic block and straight fin shapes and tested with FC-72 and HFE-7000 coolants with the objective of maximizing the heat transfer in a pool boiling configuration. A two-phase thermosyphon facility was developed to investigate the system’s performance using graphite foams of block and fin structures. The effects of foam configuration, working fluid type, and coolant filling volume on pool boiling heat transfer were analyzed. The results showed that the coolant filling volume has negligible effect on cooling performance. On the other hand, the thermosyphon performance is significantly affected by the coolant properties and the configuration of the porous graphite foam. A comparison of the Bond numbers obtained for FC-72 and HFE-7000 indicates that the bubbles have to overcome higher surface tension forces before departing the foam surface in HFE-7000. Meanwhile, the effect of the foam configuration on the boiling heat transfer performance implies that a properly designed geometry of the porous graphite foam will lead to significant enhancement of the evaporation process in a thermosyphon system.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Internal structure of “Poco” graphite foam of 75% porosity

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Figure 2

(a) Schematic diagram of designed porous thermosyphon system and (b) top view of the evaporator chamber

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Figure 3

Structures of designed (a) block and (b) fin foams

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Figure 4

Superheat versus heat flux at various coolant filling levels of FC-72 and HFE-7000

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Figure 5

Variations of heater wall temperature subjected to fin and block structures

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Figure 6

Comparison of boiling heat transfer coefficients between fin and block structures

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Figure 7

Boiling processes in (a) block and (b) fin structures at heat flux of 78 kW/m2 using HFE-7000




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