Experimental of Submerged Liquid Cooling Based on Loop Thermosiphon

This paper combines loop thermosiphon with server cooling to design and fabricate a circulating cooling system for simulating liquid cooling in servers. HFE-7100 was used as the working fluid to investigate the thermal startup issues of the servers under different heating powers and to explore the effects of varying liquid injection rates and the length of the adiabatic section in the vapor line (the height difference between the enclosure and the condenser) on the heat transfer characteristics of the circulation system. Additionally, the flow state within the vapor line during the experiment was analyzed. The research findings indicate that at low heating powers (90～120 W), the temperature of the simulated server enclosure firstly increases, then decreases, and eventually stabilizes. In contrast, at high heating powers (≥150 W), the enclosure temperature initially rises quickly, then increases slowly, and finally stabilizes. The phenomena observed during the thermal startup process can be divided into three stages: Stage 1 (from subcooled to evaporation), Stage 2 (initial establishment of the circulation system), and Stage 3 (full establishment of the system circulation). In Stage 3, the maximum temperature of the enclosure gradually decreases with increasing heating power, while the time required for the system to reach stable circulation increases with higher heating power. Furthermore, when the liquid injection rate is increased from 65% to 85%, the system pressure differential (the pressure difference between the enclosure and the liquid storage tank) increases by 34.7%, but the efficiency of the condenser is reduced, and the outlet supercooling degree will be reduced by 47.4%. When the length of the adiabatic section of the vapor line is increased from 40 cm to 80 cm, the system pressure differential increases by 26.6%, while the efficiency of the condenser improves, and the outlet supercooling degree is increased by 120.6%.