One-dimensional numerical study for loop heat pipe with two-phase heat leak model

Abstract

Heat leak (HL) has a significant influence on the thermal performance of loop heat pipes. It is difficult to measure the HL properties inside the evaporator through proper experiments. In this study, a one-dimensional numerical study is conducted for the HL simulation. A two-phase HL model is proposed, which takes into account the effects of the bubble generation on HL properties and systemic operations. Compared with the traditional conductive HL equation, the present model can clearly describe the two-phase transport characteristics in an evaporator core. The present model is validated by the experimental data of the loop heat pipe (LHP) at different heat loads and heat sink temperatures. The present model improves the prediction accuracy for radial HL in the variable-conductance mode of LHP. By coupling the one-dimensional two-phase HL model with the global LHP model, the two-phase transport properties in the evaporator core, the vapor temperatures, and the HL characteristics are investigated. Due to the existence of bubble generation, the equivalent thermal conductance between the evaporator and reservoir is increased. The HL amount is also induced to increase, which results in an increased vapor temperature especially in the variable-conductance region. The evaporator core contains the subcooled and saturated zones. The variation trends of the fluid temperature, heat transfer coefficient, equilibrium vapor quality, and void fraction are different in the two zones. The subcooled zone in the evaporator core is suggested to be enlarged in order to weaken the effects of bubbles on the system operation.