Pore size optimization and fluid channel analysis of composite wick and anti-gravity study

Abstract

Flat plate micro heat pipes (FPMHPs) utilize the vapor–liquid two-phase circulation of the working medium to transfer heat and play an essential role in heat dissipation systems. But the effects of capillary force and porosity on the flow channel’s heat transfer characteristics and the working medium’s anti-gravity properties are not clarified. It is found in the heat transfer theory that balancing the capillary force and porosity of the composite wick can improve heat transfer efficiency, increase the maximum thermal power and anti-gravity of the FPMHP. FPMHPs with composite wicks of different pore sizes were developed and tested by the established test platform. The results indicated that the capillary force and porosity of the composite wick constrained each other, and the FPMHP made of the composite wick sintered with 80 mesh copper powder (CW80-FPMHP) had the best heat transfer characteristics and anti-gravity properties. The maximum thermal power of CW80-FPMHP is 38.6 W at 0°, which is 5.4%, 3.6%, 3.5% and 17% higher than that of CW60-FPMHP, CW70-FPMHP, CW90-FPMHP and CW100-FPMHP, respectively. At a tilt of 45°, the maximum thermal power of CW80-FPMHP is 26.27 W, which is 17.6%, 24.3%, 53.9%, 53.9%, and 51.8% higher than CW60-FPMHP, CW70-FPMHP, CW90-FPMHP, and CW100-FPMHP, respectively. In addition, the thermal resistance of the vapor channel in CW80-FPMHP is lower than that of the liquid flow channel. Gravity affects the thermal conductivity of the vapor and liquid flow channels, which in turn affects the performance of the FPMHP. Balancing the capillary force and porosity can improve the performance of the FPMHP under various operating angles.