Experimental study of mechanical-capillary driven phase-change loop for heat dissipation of electronic devices and batteries

Abstract

To solve the disadvantages of traditional phase-change heat dissipation technologies, such as instability in two-phase flow and difficulty in active temperature control, a mechanical-capillary driven hybrid phase-change loop (HPCL) is designed and tested. The experiment results show that the heating power and liquid-vapor pressure difference have a decisive influence on the transformation of heat transfer modes. With the increase of heating power while maintaining the liquid-vapor pressure difference unchanged, the baseplate of evaporator undergoes four heat transfer modes, i.e. flooded, partially flooded, thin film evaporation and overheating. Among them, thin film evaporation has the significant advantages of short start-up time and high heat transfer efficiency. Meanwhile, when the baseplate temperature is maintained below 85 ℃, the heat dissipation power is enhanced by about 6.5 times if the liquid-vapor pressure difference is increased from 0 kPa to 15 kPa. Therefore, increasing the liquid-vapor pressure difference is an active means in heat transfer enhancement. The heat transfer modes distribution diagram is drawn by taking into account of power and liquid-vapor pressure difference. Transition criterions between different heat transfer modes are given. The diagram suggests that the thin film evaporation region is in the shape of “horn”. In engineering application, liquid-vapor pressure difference can be regulated adaptively according to the actual operating characteristics of heat dissipation target to achieve the optimal heat dissipation effect. Furthermore, the accurate and rapid control over baseplate temperature can be realized by controlling liquid-vapor pressure difference. In such way, the accuracy of temperature control is within ±0.5 ℃. Therefore, controlling liquid-vapor pressure difference is a simple and effective means of active temperature control.