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Research Papers: Porous Media

Effect of Wick Characteristics on the Thermal Performance of the Miniature Loop Heat Pipe

[+] Author and Article Information
Randeep Singh

Energy Conservation and Renewable Energy Group, School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, P.O. Box 71, Bundoora East Campus, Bundoora, Victoria 3083, Australiarandeep.singh@rmit.edu.au

Aliakbar Akbarzadeh

Energy Conservation and Renewable Energy Group, School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, P.O. Box 71, Bundoora East Campus, Bundoora, Victoria 3083, Australia

Masataka Mochizuki

R&D Department, Thermal Technology Division, Fujikura Ltd., 1-5-1 Kiba, Koto-Ku, Tokyo 135-8512, Japan

J. Heat Transfer 131(8), 082601 (Jun 04, 2009) (10 pages) doi:10.1115/1.3109994 History: Received August 04, 2008; Revised February 14, 2009; Published June 04, 2009

Two phase heat transfer devices based on the miniature version of loop heat pipe (LHP) can provide very promising cooling solutions for the compact electronic devices due to their high heat flux management capability and long distance heat transfer with minimal temperature losses. This paper discusses the effect of the wick properties on the heat transfer characteristics of the miniature LHP. The miniature model of the LHP with disk-shaped evaporator, 10 mm thick and 30 mm disk diameter, was designed using copper containment vessel and water as the working fluid, which is the most acceptable combination in electronic cooling applications. In the investigation, wick structures with different physical properties including thermal conductivity, pore radius, porosity, and permeability and with different structural topology including monoporous or biporous evaporating face were used. It was experimentally observed that copper wicks are able to provide superior thermal performance than nickel wicks, particularly for low to moderate heat loads due to their low heat conducting resistance. With monoporous copper wick, maximum evaporator heat transfer coefficient (hev) of 26,270W/m2K and evaporator thermal resistance (Rev) of 0.060.10°C/W were achieved. For monoporous nickel wick, the corresponding values were 20,700W/m2K for hev and 0.080.21°C/W for Rev. Capillary structure with smaller pore size, high porosity, and high permeability showed better heat transfer characteristics due to sufficient capillary pumping capability, low heat leaks from evaporator to compensation chamber and larger surface area to volume ratio for heat exchange. In addition to this, biporous copper wick structure showed much higher heat transfer coefficient of 83,787W/m2K than monoporous copper wick due to improved evaporative heat transfer at wick wall interface and separated liquid and vapor flow pores. The present work was able to classify the importance of the wick properties in the improvement of the thermal characteristics for miniature loop heat pipes.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of the mLHP experimental prototype and details of the test setup showing the temperature measurement points and locations of condenser fan and heater

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Figure 2

Combined copper wick sample showing the (a) monoporous layer as a liquid absorbing face, (b) biporous layer as an evaporating face, and (c) side view showing the layers

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Figure 3

Structure of the (a) monoporous copper sample made from 100–200 mesh size powder, (b) monoporous copper sample made from –200 mesh size powder, and (c) biporous copper sample at ×300 magnification

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Figure 4

Heat load dependence of (a) vapor temperature (Tv) and temperature difference between evaporator and compensation chamber wall (Tew-Tcc) and (b) heat transfer coefficient (hev) and evaporator thermal resistance (Rev) for wick samples A and B

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Figure 5

Heat load dependence of vapor temperature (Tv) and temperature difference between evaporator and compensation chamber wall (Tew-Tcc) for wick samples B and C

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Figure 6

Heat load dependence of vapor temperature (Tv) and evaporator thermal resistance (Rev)

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Figure 7

Relation between vapor temperature (Tv) and applied heat load for the four wick samples tested in mLHP

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