Experimental study on the startup and heat transfer behaviors of a two-phase closed thermosyphon at subzero temperatures

Abstract

In permafrost regions, two-phase closed thermosyphons (TPCTs) can be used to release heat from permafrost. TPCTs are thus embedded in foundations of infrastructures for preventing the permafrost thawing. The installation of a TPCT, however, greatly influences the efficiency of releasing heat, which has not been fully understood. To find an optimum installation for TPCTs, we experimentally studied the temperature differences and thermal resistances of a TPCT that was sequentially installed at an inclination angle of 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90° at subzero temperatures. It is found that the inner startup temperature difference varied irregularly with inclination angle. It is also found that at evaporator and condenser sections, the thermal resistance of the wall contributes negligibly to the thermal resistance of the corresponding section. Furthermore, the thermal resistances vary with inclination angle in the evaporator, adiabatic, and condenser sections. The adiabatic section has a thermal resistance that is comparable to the thermal resistance of the evaporator and condenser sections except the inclination angle of 90°. The TPCT has the minimum total thermal resistance when the inclination angle is about 20°. The results could be helpful for the optimal application of TPCTs in permafrost engineering.