Investigating the effect of powder-mixing parameter in biporous wick manufacturing on enhancement of loop heat pipe performance

This study investigated the use biporous wick with two pore sizes to enhance the performance of loop heat pipe (LHP). In the manufacturing process of a biporous wick, this paper varied the mixing ratio between high polymer PMMA, which was used to make large pores, and nickel powder, which was used to make small pores. This paper used PMMA as the sacrificial material to form large pores; the pore size and content of PMMA was varied, with powder sizes of 177-210 μm, 250-297 μm and 350-420 μm, and contents of 30 vol%, 35 vol%, and 40 vol%. After mixing with nickel powder and the sintering process to produce the biporous wick, the product was put into LHP for performance testing and measurements. Experimental results indicated that a higher content of PMMA particles corresponds to better performance, but beyond a maximum and optimal content the performance worsens; results also indicated that larger powder size leads to better vapor transport and evaporation, but beyond a certain point the large pores can cause weakened structure. Therefore, we found that 250-297 μm and 35 vol% was the optimal PMMA powder diameter and content, respectively; under these parameters, the maximum LHP heat load was 800 W, the thermal resistance was around 0.095 °C/W, the evaporator heat transfer coefficient was 131 kW/m2 C, and the porosity was 86%. Compared with using a monoporous wick, the wick performance was enhanced by about 130%, reducing the LHP thermal resistance by about 60% and, for the first time, to less than the order of 10−2 °C/W.