Evaporation heat transfer coefficient in a capillary pumped loop and loop heat pipe for different working fluids

Capillary pumped loop (CPL) and Loop Heat Pipe (LHP) are passive two-phase heat transport devices. They have been gaining importance as a part of the thermal control system of spacecraft. The evaporation heat transfer coefficient at the tooth-wick interface of an LHP or CPL has a significant impact on the evaporator temperature. It is also the main parameter in sizing of a CPL or LHP. Experimentally determined evaporation heat transfer coefficients from a three-port CPL with tubular axially grooved (TAG) evaporator and a TAG LHP with Acetone, R-134A and Ammonia as working fluids are presented in this paper. The influence of working fluid, hydrodynamic blocks in the core, evaporator configuration (LHP or CPL), and adverse elevation (evaporator above condenser) on the heat transfer coefficient are presented