Effect of the passage area ratio of liquid to vapor on an ultra-thin flattened heat pipe

Highlights: • An ultra-thin flattened heat pipe with a composite mesh wick is proposed. • Effect of the passage area ratio of liquid to vapor on the performance is studied. • The passage area ratio of liquid to vapor is adjusted by changing the wick width. • The optimum design of passage area ratio for high heat transfer is provided. -- Abstract: The effect of the passage area ratio of liquid to vapor on the heat transfer performance of ultra-thin heat pipe (UTHP) in horizontal state was experimentally investigated in this work. The wick was sintered with a layer of 100- and 180-mesh copper mesh. The passage area ratio of liquid to vapor of UTHP was adjusted by changing the wick width. The capillary limits of UTHPs with various wick widths were analyzed theoretically. The effects of the wick width and filling ratio parameters on the thermal performance of UTHPs were studied experimentally. The maximum heat transport capacity of UTHPs were compared with the calculated capillary limits. The results indicated that the optimum filling ratio of the UTHP gradually decreased with increasing wick width. An appropriate wick width was beneficial to enhance the UTHP's thermal performance by increasing the vapor-liquid circulation efficiency during heat transfer. When the wick width was 4 mm, the maximum heat transport capacity of UTHP could reach 8.5 W, which was 4.25 times that of UTHPs with 2 and 7 mm wide wicks. From the capillary limit calculation and sample testing, the optimum passage area ratio of liquid to vapor of the experimental UTHP was 67.28%.