Experimental study on the heat transfer performance of loop heat pipe with different particle morphology and wettability of porous wick

Abstract

Particle morphology and wettability of porous wick affect the movement and distribution of the working fluid in wicks, which further affects the phase change heat transfer. So the heat transfer performance will be significantly different for loop heat pipe (LHP) with different porous wicks. To study the effects of particle morphology and wettability of porous wick on the heat transfer performance of LHP from the perspective of phase separation, four types of porous wicks were fabricated and applied in LHP. Porous wicks were sintered with spherical and dendritic particle copper powder, respectively. Superhydrophilic wicks can be obtained by H2O2 oxidation. The results showed that capillary performance of dendritic particle wick was better than that of spherical particle wick. At t = 470 s, the climbing height of distilled water in the hydrophilic dendritic and spherical particle wicks were 19.8 and 18.1 cm, respectively. Compared with hydrophilic wick, superhydrophilic wick has a maximum 2.0 cm enhancement in climbing height at present experiments. The particle morphology of porous wicks had great effects on the heat transfer performance of LHPs. For LHPs with spherical or dendritic particle wick before H2O2 oxidation, their operating temperatures were 73.5 and 68.9 °C under θ = 90°, Q = 220 W situation. The latter has a lower operating temperature. For LHP with superhydrophilic dendritic particle wick, it had the best heat transfer performance among four kinds of LHP. The minimum thermal resistance can reach 0.07 K/W at Q = 300 W. Two diffusion modes of liquid in porous wicks were found in the visualization experiment, the distribution of the working fluid in dendritic particle wick was more uniform than that of spherical particle wick, which can explain well that the temperature of evaporator bottom surface is more uniform for LHP with dendritic particle wick. These results have a good guiding role for the preparation of high-performance LHP.