Experimental investigation on the heat transfer characteristics of loop thermosyphon with a micro-channel evaporator under low heat flux

Abstract

Loop thermosyphon is an efficient heat transfer device increasingly used in solar energy applications. The heat flux offered by solar radition is relatively restricted, but the mechanism of heat and mass transfer in loop thermosyphon at low heat flux remains ambiguous. Hence, a low heat flux loop thermosyphon experimental test platform was proposed and constructed in this paper to investigate the influences of filling ratio, heat load and cooling water temperature on the start-up and operation characteristics of the system. The outcomes reveal that instances of local dry-out, temperature overshoot, and geyser boiling are witnessed throughout the experimental process. With an increase in the filling ratio, the occurrences of local dry-out and geyser boiling gradually decrease and disappear, while the temperature overshoot becomes more prominent. The system’s optimal filling ratio is found to be approximately 80 %, and the lowest thermal resistance is 0.0053 K/W. No heat leakage is observed from the bottom of the evaporator to the liquid line. Except for the 40 % filling ratio, the system’s heat transfer efficiency exceeds 94 % for all other filling ratios, and the heat transfer performance is outstanding. The research results will contribute to the enhanced application of loop thermosyphon in solar energy utilization, possessing practical engineering significance. Additionally, they can also enhance the heat and mass transfer mechanisms of loop thermosyphon, having certain academic significance.