Effect of Height Difference on The Performance of Two-phase Thermosyphon Loop Used in Air-conditioning System

Two-phase thermosyphon loops (TPTLs) are widely used in air-conditioning field for heat recovery and free cooling utilization in recent years. The height difference between the condenser and the evaporator is always considered as the driven force of thermosyphon. However, experiments show the cooling capacity of the TPTLs is not linearly improved with the increase of the height difference. So, the influence mechanism of height difference on the performance of TPTLs is not clear and needs more deep investigation. In this study, a visual experimental setup is established, and the effect of height difference and circulation resistance on the performance of TPTL is investigated. The results shows that with the increase of the height difference, the liquid head rises continuously until remain stable approximately. Therefore, the liquid head is less than the height difference in some cases, which means that the downcomer is partially liquid filled. Consequently, with the increase of height difference, the circulation flow rate and thermal performance firstly increases then remains constant, rather than continuous increase in the traditional understandings.