Heat transfer performance of a two-phase closed thermosyphon with different inclination angles based on the core-tube monitoring

Two-phase closed thermosyphons (TPCTs) have been widely used in permafrost regions because of their good cooling effect. The variation in the inclination angle of TPCTs significantly affects the heat transfer process and temperature distribution inside TPCTs, which is still not fully un-derstood. This study experimentally investigated the heat transfer performance of TPCTs with inclination angles varied from 0 degrees to 90 degrees with 10 degrees intervals. In addition to the outer wall tem-perature and heat flux, the thermal regime of the working medium inside TPCT was simulta-neously monitored based on the core-tube. Experimental results show that the temperature distributions inside TPCT along the axial direction vary regularly with inclination angle. The heat transfer rates of the evaporator and condenser sections change nonmonotonically and nonlinearly with the inclination angle. The influence of the inclination angle on the thermal resistance is greater in the evaporator and the adiabatic sections than in the condenser section. Consequently, a TPCT at 10 degrees produces the best heat transfer performance, corresponding to the best isothermal characteristics, the maximum heat transfer rates of the evaporator and condenser sections, and the minimum total thermal resistance. This study provides a reference of monitoring method for further research on TPCT.