Experimental study on a R134a loop heat pipe with high heat transfer capacity

Loop heat pipe (LHP) promises great application potential in electronics cooling. However, the selection of environmentally friendly working fluid remains a big issue, especially in commercial applications. Although R134a is a common refrigerant, the R134a-charged LHP is limited by small heat transfer capacity (HTC). In this work, a LHP with R134a as the working fluid is designed and fabricated. In order to enhance its HTC, the structure optimization has been made based on the theoretical analysis of flow resistance where the smaller wick thickness and larger diameter of the vapor and condenser lines are adopted. Experimental results show that the R134a LHP can reach a high HTC up to 250 W at the horizontal orientation with the condenser cooled by air forced convection. With an adverse elevation of 5 cm, the HTC is reduced to about 230 W. In addition, an extensive experimental study on its startup characteristics with the heat loads ranging from 5 to 30 W is conducted. The influence of the initial liquid/vapor distribution in the evaporator on the startup performance is investigated. This work proposes an effective method to enhance the HTC of the R134a LHP, which contributes greatly to its structure optimization and future commercial applications.