In this paper, experiments were conducted to achieve a better understanding of the oscillating heat pipe (OHP) operating behavior with water and ethanol as working fluid. The experimental results showed that there existed a necessary temperature difference between the evaporator and the condenser section to keep the heat pipe working. The maximum effective conductivity of the water OHP reached up to $259 kW/m K$, while that of the ethanol OHP is of $111 kW/m K$. Not all the OHPs are operated in the horizontal operation mode. The heat transfer performance of the ethanol OHP was obviously affected by the filling ratio and the inclination angle but the influence law is irregular. The effect of the filling ratio and the inclination angle of the water OHP were smaller than that of the ethanol one. The heat transfer performance of the OHP was improved with increase of operating temperature. The startup characteristics of the OHP depended on the establishment of the integral oscillating process, which was determined by the operating factors. The startup temperature of the ethanol OHP varied from $40°C$ to $50°C$ and that of the water, OHP varied from $40°C$ to $60°C$ without considering the horizontal operating mode. The water OHP showed a better performance and more stable heat transfer characteristics than the ethanol OHP, which had no obvious advantages of the startup capability as well.

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