Numerical study of flow and heat transfer in the vapour grooves of a loop heat pipe evaporator

A three-dimensional numerical study is developed to investigate the heat and mass transfer in the vapour removal channels of a Loop Heat Pipe (LHP). The heat transfer governing equations and the Navier-Stokes equations are solved under steady-state conditions for two vapour removal channel configurations: when the channels are in the wick and when the channels are in the casing. The boundary conditions for both configurations are extracted from numerical simulations using a model of the evaporator in which the modelization of the transfers in the wick is based on a pore network model. The results show that assuming that the vapour temperature in the channels is close to the saturation temperature is acceptable when the channels are within the wick but questionable when the vapour removal channels are within the casing. The simulations also indicate significant variations of the wall temperature between the various channel limiting surfaces. The heat transfer coefficient is different on the various surfaces and cannot be predicted using standard correlations for convective heat transfer in pipes.