Loop Heat Pipes with Sintered Nickel Wick Structures Skewed Pore Size Distribution.

Loop heat pipes（LHPs）,which possess the advantages including high transfer capacity, long transport distance, self-priming and active control, have great potential for spacecrafts and electronic cooling. The main purpose of this study is to enhance the performance of miniature LHPs. According to the literatures, when a LHP is miniaturized for electronic cooling, its performance would become more sensitive to the structure of the capillary wick in the evaporator. Traditionally, mono-porous sintered wicks were used in LHPs; however, the pore size distribution of mono-porous wick is intolerant of boiling inside the capillary structure, which leads to dry-out in capillary structure. In order to improve this drawback, this study manufactures the wick structure with skewed pore size distribution by using two particle sizes of the same material. Such a wick structure incorporates the higher capillarity of small-size pores and the better permeability of big-size pores. In the experiments, different mixing ratio and sintered temperature were used to control skewed level of pore size distribution. The thermal performances of wicks with skewed pore size distribution were then tested and a comparison was made between mono-porous wicks and the wicks with skewed pore size distribution for the heat transport capability of the LHP.
The present experimental results show that the wick with skewed pore size distribution can make the vapor generated at high heat flux vents smoothly, and hence enhance the performance of LHPs. With the mixing ratio of 75% and the sintering temperature of 700℃, the manufactured LHP achieves the heat capacity of 200W at the allowable evaporator temperature of 85℃ and thermal resistance is 0.367℃/W. In comparison with a mono-porous wick, the performance is enhanced about 100%. The wick structures with skewed pore size distribution have not only increased the heat transfer performance but also reduced the thermal resistance. With this kind of wicks, LHPs would have more attractive applications to high heat flux in the future.