Effect of Wick Characteristics on Heat Transfer by Using Lattice Boltzmann Method in a Loop Heat Pipe
Date Issued
2011
Date
2011
Author(s)
Huang, San-Yu
Abstract
Loop heat pipes(LHPs) are efficient two-phase heat transport devices and have been applied to thermal management in space application. The evaporator and wick’s structure are important components in a loop pipe. The wick’s properties which include the porosity, the permeability, and the pore size distribution are essential. However, most of the mathematical models were developed without considering the relationship among these properties. The range of application and prediction for LHPs will be therefore restricted.
The purpose of this work is to develop a mathematical model and to discuss the relationship between the wick’s properties and heat transfer performance. The modeling strategy is as follows: (1) A flow field is established with random particle packing by controlling porosity and particle size. (2)The permeability is calculated by the Lattice Boltzmann Method for the flow field. (3)The pore size distribution is simulated in the packing medium. The heat transfer performance of the LHPs was discussed with different particle sizes and porosities using ammonia as the working fluid at horizontal and vertical operating conditions. The mean absolute errors of wick’s properties as well as the thermal performance prediction did not exceed 37%.
The modeling results showed the permeability and the pore size were increased with a larger particle size and a higher porosity. At horizontal operating condition, the higher permeability and average pore size were beneficial for the supplying of working fluid and vapor exhaust. This reduced the vapor blanket and thermal resistance in the wick structure. However, at vertical operating condition, the bigger pores formed by larger particles was disadvantageous for capillary pumping force; and the smaller particles retarded the supplying of working fluid. Therefore, it caused a reduction of heat transfer performance. In conclusion, the development of this work is proved to be a useful tool for the prediction in LHP heat transfer performance.
Subjects
loop heat pipe
lattice Boltzmann method
pore size simulation
Type
thesis
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