Modeling and experimental investigation of looped separate heat pipe as waste heat recovery facility

A looped separate heat pipe as waste heat recovery facility for the air-conditioning exhaust system has been developed in this work. A one-dimensional steady-state model is presented for determining the upper and lower operating boundaries of the initial filling ratio of the working fluid, as a function of the separate heat pipe geometry, vapor temperature of working fluid and power throughput, combined with two-phase heat exchange characteristics and distribution of the liquid film velocity along with the liquid film thickness direction. A parametric analysis is performed to investigate the effects of the length of the evaporator, vapor temperature, and power throughput on the critical values of the upper and lower boundaries. Simulation results show that the length of the evaporator makes almost no influence on the upper boundary, but great effect on the lower boundary. An increase of the vapor temperature leads to the easier arriving of the lower boundary. Moreover, operation ranges of the separate heat pipe vary with the working fluids. Water and methanol were used separately. An experiment was implemented to validate the simulated results. The numerical predictions compare favorably with experimental results.