Simulation of complete liquid–vapour phase change process inside porous evaporator using local thermal non-equilibrium model

• Complete liquid–vapour phase change inside porous media has been considered.
• Two-phase mixture model has been used along with local thermal non-equilibrium condition.
• One dimensional phase change problem is considered as demonstrative example.
• Smoothing of effective diffusion coefficient is required as remedy.
• Axial diffusion strongly influences initiation and termination of phase change process.

The present article demonstrates the necessity and the usefulness of a newly proposed smoothing algorithm for the effective diffusion coefficient in order to avoid non-physical “jump” in the predicted properties during numerical simulations of the complete liquid–vapour phase change process within porous media. The formulation is based on the two-phase mixture model (TPMM) along with the assumption of local thermal non-equilibrium (LTNE) condition where the governing equations have been solved using the finite volume method. For the purpose of demonstration, one-dimensional phase change problem of water has been considered. Comparison between results obtained with the local thermal equilibrium (LTE) and LTNE models indicates that wherever applicable, particularly for lower inlet Reynolds number and higher heat input, the latter should be used. The effect of employing different models for the partitioning of wall heat flux using LTNE model has been found negligible owing to the very high convective heat transfer coefficient between the solid and the fluid phases. A representative parametric study suggests that the diffusive energy transport process in the upstream direction through the solid and the fluid phases has a strong influence on the initiation and the termination of the phase change process.