Computational model and simulation of DCMD desalination systems with heat recovery

Abstract

Desalination technologies can help mitigating the water scarcity problem facing humankind. Membrane distillation (MD) is a desalination technology attractive for its adequacy to use low-grade waste heat or renewable energy sources. This work addresses the modelling of a Direct Contact Membrane Distillation (DCMD) plant with heat recovery. The desalination unit comprises several DCMD modules, each of a shell and hollow fibre tube bundle type. A multiscale approach is needed to address the problem. It includes modelling of the vapour flux through the micro/nano porous membrane, models for the mass and energy conservation at the scale of a single DCMD module, and thermodynamic modelling at the scale of the desalination plant. Analytical solutions of the mass and heat transfer across the membranes are combined with finite volume discretised equations describing heat and mass conservation for the feed and permeate streams. An iterative scheme is devised to solve the model equations in order to determine the flow and temperature variables in the DCMD module. The computational model predictions show good agreement with experimental data available in the literature. Finally, the methodology presented herein is used to simulate the performance of a DCMD desalination plant with heat recovery.