Evaluation of Thermal-Hydraulic Behavior in a Loop Heat Pipe by Image Analysis

A loop heat pipe (LHP) is a high-efficient two-phase heat transfer device that utilizes evaporation and condensation requiring no electrical power. In addition, LHP having multiple evaporators including compensation chambers (MLHP) is capable of heat load sharing among evaporators. Thermal-hydraulic behaviors in the evaporators of MLHP under the heat load sharing mode have not been sufficiently clarified. Hence, this paper aims to investigate the thermal-hydraulic behaviors in case of MLHP having two evaporators while visualizing inside the evaporators with borescope cameras. As a result, the heat load sharing mode could be classified into two modes in accordance with a quantity of heat absorbed at the evaporator that not be received any heat load. In one mode (named mode A), a heat sharing ratio between evaporators increased as the quantity of heat absorbed increased. On the other hand, in the other mode (named mode B), the heat sharing ratio became constant at any quantity of heat absorbed. In addition, a numerical model to predict a transition from mode A to mode B was developed. The numerical model was good agreement with the experimental data.