Theoretical analysis of steady-state operating characteristics of a cryogenic loop heat pipe

Based on energy balance, pressure balance and mass conservation, a steady-state mathematical model of a cryogenic loop heat pipe (CLHP) with nitrogen as the working fluid was established in this paper, and the modeling results showed good agreement with the experimental data. Theoretical investigation of the steady-state operating characteristics of the CLHP was conducted based on the mathematical model, where the effects of the parasitic heat load and power applied to the secondary evaporator on the performance of the CLHP was studied. The conclusions below were drawn: the heat transport capability of the CLHP is obviously reduced as compared with ambient loop heat pipe; when the heat load applied to the primary evaporator is small, the steady-state operating temperature is high due to the existence of the parasitic heat load and adverse elevation. However, the performance of CLHP at small heat loads can be notably improved by applying heat load to the secondary evaporator. The maximum operating temperature/pressure drops as the volume of the gas reservoir increases, and the maximum heat transport capability of CLHP will be limited accordingly.