Experimental study on the thermal performance of an ammonia loop heat pipe using a rectangular evaporator with longitudinal replenishment

Abstract

• An ammonia LHP with a rectangular evaporator was designed and fabricated. • The LHP can successfully realize the startup at small heat loads as low as 2 W. • The LHP responds quickly to the heat load change and achieves a smooth transition. • The LHP can reach a heat transfer limit up to 110 W restricted by capillary limit. • Heater area and position play an important role in the heat transfer limit. In this work, a stainless steel-ammonia loop heat pipe (LHP) using a rectangular evaporator with longitudinal replenishment was designed and fabricated. Extensive experiments have been implemented to investigate its startup characteristics, dynamic operation, heat transfer limit and thermal resistance. In particular, the effect of heat load on the startup performance was evaluated, and the effects of heater area and position on the heat transfer limit were studied. Experimental results showed that the LHP exhibited excellent startup performance. It could realize the startup successfully at a small heat load as low as 2 W. In most cases, it started up in only one situation. The temperature overshoot decreased with the increase of the heat load in the startup. In the power step change process, the LHP responded quickly to the changes of the heat load, and achieved a smooth transition. The LHP could reach a heat transfer limit up to 110 W for all the three heaters, restricted by the capillary limit. The heater area and position played an important role in the heat transfer limit, which became larger when the heater was placed closer to the compensation chamber (CC), due to reduced flow resistance of liquid replenishment in the capillary wick. It was found that the closer the heater was located to the CC, the smaller the thermal resistance of the LHP system. This work contributes to a comprehensive understanding of the thermal performance of the LHP using a rectangular evaporator, providing good guidance and reference for its future applications.