Heat and Mass Transfer in Evaporator of Loop Heat Pipe

Investigation of heat-exchange processes in the evaporator of a loop heat pipe is important for the development of heat transfer devices with low thermal resistances. A two-dimensional mathematical model of the evaporator active zone is presented. Three modes of vapor generation in the wick have been examined, where each differs in the mechanism of the vapor phase formation and in the saturation of the capillary structure: 1) evaporation to the vapor grooves, 2) volumetric evaporation in the two-phase zone, and 3) volumetric evaporation in the two-phase zone separated from the heated wall of the evaporator by dried zones. Conditions identifying changes between modes have been formulated. Structural characteristics of the wick with different pore sizes have been taken into account. Using a numerical-analytical method, results were obtained for three copper loop heat pipes with biporous wicks, where the working fluid was water for one of the loop heat pipes and methanol for the other two. The heat-load dependent temperature drop between the evaporator wall and the vapor in the vapor grooves has been presented. Additionally, a comparative analysis of calculated and experimental results was performed.