Numerical simulation of complete liquid–vapour phase change process inside porous media: A comparison between local thermal equilibrium and non-equilibrium models

Abstract

The Complete liquid-vapour phase change process inside an asymmetrically heated porous channel has been numerically investigated in this article, based on the Two-Phase Mixture Model (TPMM), while employing both Local Thermal Equilibrium (LTE) and Non-Equilibrium (LTNE) conditions. For the latter condition, four different models have been considered for the partitioning of imposed wall heat flux. All simulations have been carried out by applying the recently proposed smoothing algorithm for the effective diffusion coefficient, without which, the occurrence of non-physical “jump” in the predicated properties, across the interface between the single and the two-phase regions could not be always avoided. The governing equations have been discretised using the finite volume method on a fixed staggered grid layout and solved iteratively in a SIMPLE-like manner. Only the imposed wall heat flux has been varied, while all other parameters and properties have been kept fixed during the present investigation. It has been observed that LTE model fails to produce realistic predictions, particularly when the superheated vapour phase is formed inside the evaporator. On the other hand, the conduction heat transfer through the solid phase and the internal heat exchange between the solid and the fluid phases across the interface separating the superheated vapour and the two-phase mixture regions provide two additionally required mechanisms for LTNE model for the realistic predictions. As far as different models for the partitioning of wall of heat flux is concerned, Model-2 appears to be the most realistic, while Model-1 has been found to be the most stable.