Experimental study on effective range of miniature oscillating heat pipes

A series of experiments were performed to investigate the effect of heat transfer length and inner diameter on the heat transport capability of miniature oscillating heat pipes (MOHPs). In the experiments, MOHPs with heat transfer length (L) of 100, 150 and 200 mm, consisting of 4 meandering turns and inner diameter of 0.4, 0.8, 1.3 and 1.8 mm were adopted, and pure water was used as the working fluid. The results show that increasing inner diameter or decreasing heat transfer length is beneficial to MOHPs startup. An effective range of MOHPs has been identified. The recommended inner diameter of MOHPs should be bigger than 0.8 mm in vertical bottom heating mode, while the heat transfer length should be controlled less than approximately 100 mm in horizontal heating mode. For high heating power, the thermal performance of MOHPs can only approach that of sintered heat pipes in horizontal heating mode, while exceed it in vertical bottom heating mode. Finally, the dominating dimensionless parameters, including Di/L, Ja, Bo and Wa, are used to predict the heat transport capability of MOHPs. The correlation prediction agrees with the experimental results fairly well.