Advanced analysis of an ammonia loop heat pipe for space applications. Part II: numerical results

A novel and advanced thermal model is proposed for nonstationary simulations of a loop heat pipe (LHP) with variation of the heat power loads and the boundary heat flux conditions. The thermal system has two ammonia-filled LHPs, with the heat loads distributed between the LHPs depending on the temperature gradients on the radiator. Since one critical problem for the thermal simulation of orbital conditions is linked to the long computational times, a novel, adaptive, and fast model for a LHP, based on a thermal model built using the lumped parameters code, was built in order to get CPU times lower than the real times of the flying device. Consequently, the LHP fluid part is switched on and off according to the heat power level toward the evaporator and taking into account the capillary limit under which no pumping force is generated in the porous wick. Such an indication is also applicable to any commercial and noncommercial code, once the complex LHP parameter set is known. In particular, the computational times have been reduced by a factor of 14 with respect to standard-space LHP simulations, allowing a sensitivity analysis of the various parameters.