Effect of filling rate and inclination angle on the heat transfer performance of two-phase closed thermosyphon in permafrost regions
Two-phase closed thermosyphons(TPCTs)play a significant role in permafrost regions due to their thermal semiconductor effect.Many TPCTs have been used to collect cold energy from the ambient air in perma-frost regions to cool the underlying stratum.In this study,an ammonia-steel TPCT test bench suitable for perma-frost regions was built to optimize the working conditions of the TPCT.The effects of filling rate and inclination angle on the heat transfer performance of low-temperature TPCTs were analyzed.Experiments were carried out at different filling rates(20%,30%,40%)and inclination angles(10°,30°,50°,70°,90°)under negative temperature conditions.To simulate low-temperature conditions,the ambient temperature difference between the evaporator section and the condenser section was set to 13℃.The heat transfer performance of the TPCT was evaluated based on the temperature distribution inside and outside the TPCT and the variation in the heat flux density of the outer wall.The heat transfer performance of the TPCT was evaluated using indexes such as isother-mal characteristics,thermal resistance,and transfer efficiency.The experimental results show that,under three experimental filling rates,all TPCTs with an inclination angle of 10° have the best axial internal isothermal per-formance.The minimum thermal resistance occurs at an inclination angle of 50° when the TPCT filling rates were 30%and 40%,corresponding to the highest heat transfer efficiency.For the TPCT with a filling rate of 20%,the minimum thermal resistance and the highest heat transfer efficiency both occur at an inclination angle of 30°.Overall,the TPCT with a filling rate of 30%has the optimal heat transfer performance.It is recommend-ed that the inclination angle of TPCTs is between 10° and 50°.This study provides meaningful reference for the best structural parameters in the design of TPCTs for cold regions engineering.
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