Effect of localized dry-out on startup and steady-state operation characteristics of ethanol-based oscillating heat pipes

It's a significant challenge to choose a suitable heat dissipation method in different electronics assembly environments requiring different heat transfer distances. Oscillating heat pipes are promising heat exchangers, but localized dry-out during operation leads to an unstable heat transfer and limits further application of oscillating heat pipes. To extend the applicability of oscillating heat pipes, it is essential to reveal the localized dry-out characteristics under various heat transfer distances. In this study, the impact of localized dry-out on the multi-stage operating characteristics of ethanol-oscillating heat pipes with various heat transfer distances was investigated through partial visualization experiments. The anti-dry-out capacity of ethanol-oscillating heat pipes was quantitatively evaluated and compared with that of water-oscillating heat pipes. The experimental results revealed that the dry-out performance was closely related to the flow motion of the operating fluid. The stagnation of the operating fluid was the primary cause of localized dry-out. Localized dry-out deteriorated the startup and heat transfer performances of oscillating heat pipes. The anti-dry-out capacity first improved and then diminished as the heat transfer distance increased. The results also revealed that ethanol exhibited superior dry-out performance compared to water, especially at long heat transfer distances. Besides, an empirical correlation equation was fitted to evaluate the anti-dry-out capacity of oscillating heat pipes under different heat transfer distances based on the experimental results. The empirical correlation equation about the Ku number could be a reasonable predictor of the anti-dry-out capacity of oscillating heat pipes. The predicted results were in good agreement with the experimental results, with 86 % of the data deviating within +/- 20 % and an average standard deviation of 19.72 %. This research closed the gap in the prediction for the anti-dry-out capacity and provided a valuable reference to broaden the applicability of oscillating heat pipes.