Experimental study on the effects of filling ratios on heat transfer characteristics of liquid metal high-temperature oscillating heat pipes

Abstract

The liquid metal high-temperature oscillating heat pipe (LMHOHP) is a kind of oscillating heat pipe with liquid metal as the working fluid, which can work efficiently in high-temperature environments over 500 ℃. In this paper, in order to master the effects of the filling ratio on the performance of the LMHOHPs, the start-up performance, the flow state, and the heat transfer performance of LMHOHPs were studied by experiments. The working fluid of LMHOHPs was sodium-potassium alloy with the potassium mass fraction of 78%. Under the input powers of 1500–3500 W and the inclination angles of 0–90°, LMHOHPs with filling ratios of 11–88% were tested. The experimental results showed that: (1) The LMHOHPs with filling ratios of 22–80% could successfully start up, and the heat transfer process was carried out by oscillation flow of the working fluid. The start-up mode varies with the filling ratio, and the start-up temperature increased with the increasing filling ratio. (2) With the filling ratios of 35–64%, the flow states of the LMHOHPs could change from the oscillation flow to the unidirectional circulation flow, and the heat transfer performance was significantly enhanced. With the increase of filling ratio, the required input power at the transition of the flow state decreased. (3) When the inclination angles were 30–90°, the thermal resistance of LMHOHPs decreased firstly and then increased with the filling ratio, and the achieved minimum thermal resistance was 0.081 ℃/W when the filling ratio was 48%. However, when the inclination angle was 0°, the thermal resistance of LMHOHPs monotonically increased with the filling ratio.