Investigation on liquid-vapor interface behavior in capillary evaporator for high heat flux loop heat pipe

Abstract

This paper reports a theoretical and experimental study on a thermo-fluid dynamics in an evaporator of a loop heat pipe (LHP). A steady-state model that includes liquid–vapor interface behaviors in the evaporator was developed. In this model, the changes in the heat transfer coefficient of the evaporator were considered. A flat-type evaporator was designed on the basis of the LHP model. The main characteristics of the evaporator are as follows: the number and width of the vapor grooves that were processed in a porous wick were 85 and 0.3 mm, respectively. As results of the experiments, the LHP transported heat up to 260 W (18.2 W/cm2) for the heat transport length of 550 mm. The minimum thermal resistance of the LHP was 0.13 K/W. The operating temperature of the experimental result agrees well with the calculation result. The liquid–vapor interface behaviors in the evaporator during the LHP operation were discussed. On the basis of the model, the relation between the liquid–vapor interface behaviors and the heat transfer performance of the LHP was quantitatively explained. In addition, it was found that the contribution of the nucleate boiling heat transfer increased with the applied heat. This phenomenon enhanced the heat transfer performance at high heat flux.