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

Abstract

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 26,270 W/m2 K and evaporator thermal resistance (Rev) of 0.06–0.10°C/W were achieved. For monoporous nickel wick, the corresponding values were 20,700 W/m2 K for hev and 0.08–0.21°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 83,787 W/m2 K 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.

Development of cryogenic loop heat pipes: A review and comparative analysis

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Cold Energy Storage Systems Using Heat Pipe Technology for Cooling Data Centers

“…Unlike conventional heat pipes in which wick structure is built on the internal wall of the pipe, the thermosiphon internal wall has none wick to be built. As well known, the function of the wick is for capillary of liquid from condenser section to evaporator section in the heat pipe and vaporizing the liquid when heat is applied at the heating area (Zhang et al, 2002 andSingh et al, 2009).…”

A numerical comparative study of the effect of working fluids and wick properties on the performance of capillary pumped loop with a flat evaporator

“…Experimental results showed that the LHP-acetone start up is faster than the LHPmethanol and its evaporator wall temperature is lower at steady state. Singh et al [18] studied the effect of wick characteristics on the thermal performance of the Miniature Loop Heat Pipe. Different materials and porous structures have been investigated to improve the efficiency of the heat exchange process inside the evaporation zone.…”