Analysis of non-uniform heat loads on evaporators with loop heat pipes

Loop heat pipes (LHPs) are passive two-phase heat transfer devices which are widely used in cooling applications such as spacecraft thermal control and electronics cooling. As these devices often encounter non-uniform heat load during operation, a numerical analysis based on a 2-dimensional dynamic mesh model is conducted to gauge the influence of non-uniform load on the performance of a flat-plate evaporator used in LHPs. The variations of evaporation heat transfer coefficient, outflow working fluid temperature, vapor and liquid interface position as well as surface temperature with heat load concentration are analyzed. The results reveal that when the heat load is not highly concentrated and relatively low, non-uniformity facilitates the heat transfer. On the other hand, highly non-uniform heat load will deteriorate heat transfer. Furthermore, the maximum surface temperature will increase significantly under non-uniform heat flux, although the phenomenon can be mitigated by using shell materials with higher heat conductivity.