Development of a loop heat pipe with kW-class heat transport capability

Abstract

This paper describes the design, fabrication, and heat transfer characteristics of a loop heat pipe (LHP) with a kW-class heat transfer performance. A one-dimensional numerical model incorporating a two-phase flow pattern of the LHP condenser was developed during the design process. Based on the numerical model, a kW-class LHP comprising a single evaporator was constructed. At the evaporator, a stainless steel 316 (SUS316) box-type wick was installed, and pure water was used as the working fluid. Additionally, two types of condensers with diameters of 1/2 and 3/4 in. were manufactured based on the devised numerical model. An experimental investigation of the heat transport performance of the kW-class LHP was conducted under a cooling temperature of 30 °C using four conditions of heat dissipation at the condenser: natural air, forced air, natural water, and forced water convection. The world’s highest heat transport of 6.2 kW was achieved using the 1/2-in. diameter condenser under natural water convection. The thermal resistance between the evaporator and condenser was 0.004 °C/W, and annular flow dominated the condenser’s flow pattern. Under the other cooling conditions, maximum heat transport capabilities of 1.5, 2.5, and 4.5 kW for natural air, forced air, and forced water convection, respectively, were achieved. Conversely, due to vapor penetration from the condenser to the compensation chamber caused by stratified flow at the condenser, lower LHP performances were demonstrated by the 3/4-in. condenser under all cooling conditions. The findings confirmed that to improve heat transfer performance, the appropriate control of the two-phase flow pattern at the condenser is critical, and it is essential for the development of kW-class LHPs.