Mathematical Model of a Loop Heat Pipe with Phase-Change Heat Transfer in a Wick Structure
Date Issued
2008
Date
2008
Author(s)
Huang, Chi-Ting
Abstract
A mathematical model for Loop heat pipes (LHPs) can provide a straightforward method of design analysis and performance improvement. However, most of mathematical models were developed for the specific component, either for a wick or a compensation chamber. These models ignored the phase-change heat transfer or the pore size distribution of a wick structure. It will restrict the range of application and prediction of the model. An improved 1-D steady state model was developed in this study. The phase-change heat transfer and the pore size distribution of a wick structure were also taken into account. The evaporator surface temperature was calculated as a function of the heat load. Both of the monoporous wick and biporous wick can also be predicted, the comparison between the predicted results and experimental data are within 23%. The effects of pore size distributions in the wick’s performances were studied by this model. Results of this study showed the different pore size distributions will influence the vapor blanket extent of the wicks, which can be estimated by the thermal resistance. This thermal resistance dominates the heat transfer performance of the wick and thus can be considered as a standard for the wick’s heat transfer capacity. Because the narrow pore size distribution of the monoporous wick would accumulate gradually to form the vapor blanket, it brings the higher thermal resistance with increasing heat flux. As the heat load increased to 500W, the thermal resistance of the vapor blanket would reach to 0.16℃/W, and 60% of the total thermal resistance(0.26℃/W). The large pores in the biporous wick play the role as the path way for vapor to escape, and thus the performance is affected less by the vapor blanket. The size and amount of larger pores in the biporous wicks was analyzed to investigate the heat transfer capacity of the LHP by this model. The Results indicate that the large pores with reducing size and increasing amount have better performance. The optimized biporous wick can obviously reduce the thermal resistance of vapor blanket to 0.002℃/W, only 2% of the total thermal resistance(0.1℃/W), on the other hand, the biporous wick can not only effectively eliminate the thermal resistance of vapor blanket but also improve the heat transfer capacity of the LHP.
Subjects
Loop heat pipe
pore size distribution
monoporous wick
biporous wick
phase-change heat transfer
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-97-R95522312-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):cadb35287f30b509a10834fca70e2d1c