Visualization study on the heat and mass transfer in the evaporator-compensation chamber of a loop heat pipe

To visually analyze the flow and heat transfer characteristics of the working fluid in a loop heat pipe (LHP), the evaporator-compensation chamber (CC) was designed as a half-sectioned cylindrical structure sealed with a glass window. Using acetone as the working fluid, visualization experiments were performed under different heat loads and tilt angles. The vapour-liquid distribution in the evaporator-CC coupling structure and the temperature variation characteristics of the LHP system were investigated at three tilt angles of the evaporator-CC coupling structure. According to the experimental results including the startup and steady-state operation, some important conclusions have been drawn as summarized below: (1) with the subcooled liquid outflow from the bayonet tube, the vapour-liquid interface in the evaporator-CC coupling structure rises when the heat load is applied to the evaporator; (2) the bubble generation inside the porous wick becomes more intense with an increased heat load, and there are various bubble movement patterns at different tilt angles; (3) the temperature fluctuation of the LHP system is closely related to the oscillation of the vapour-liquid interface in the evaporator core.