Three-dimensional lattice Boltzmann investigation on pore scale liquid–vapor distribution patterns and heat transfer performance of a loop heat pipe heterogeneous porous wick evaporator

Abstract

The pore scale numerical simulations on evaporation of a three-dimensional heterogeneous porous wick capillary evaporator used in a loop heat pipe (LHP) are realized through using a lattice Boltzmann method with liquid–vapor phase change. The dynamic liquid–vapor interface characteristics are obtained. The steady-state wick state and heat transfer performance as well as the influences of wick porosity and surface wettability are discussed. It is found that as heat flux increases, the wick state changes from the fully saturated state at low heat fluxes, to the partial dryout state at medium heat fluxes, and finally to the complete dryout state at high heat fluxes. The effective heat transfer coefficient of evaporator firstly grows slowly for the saturated wick, then increases rapidly and reaches a maximum value at partial dryout wick state, but afterwards drops sharply when the wick starts to be complete dryout. With the decreasing of wick porosity and contact angle, the heat flux to achieve the maximum effective heat transfer coefficient is increased and the complete dryout state is postponed. In the present range of parameters, the maximum effective heat transfer coefficient is improved by reducing wick porosity, while it is barely affected by contact angle.