Simulation of heat and mass transport for ethylene glycol solution separation using a vacuum membrane distillation process

In this research, a comprehensive model was extended to study the effects of different vacuum membrane distillation (VMD) parameters in flat membrane modules. The model is based on computational fluid dynamics (CFD) which uses the finite element method (FEM) as a powerful tool to solve different partial differential equations (PDEs) simultaneously. COMSOL Multiphysics as a commonly used software for problems involving Navier-Stokes and mass conservation equations based on FEM, was used. Furthermore, the fugacity coefficient was used in order to calculate vapor and liquid activity coefficients. Vacuum membrane distillation was used as a separation method for ethylene glycol (EG) solution separation using a flat polypropylene (PP) membrane module. Flow distribution through the membrane was obtained by two mass transfer mechanisms; Knudsen and free diffusion. Furthermore, the calculated vapor pressure using the UNIQUAC method was used as a reference vapor pressure. Effects of operating parameters comprising feed temperature, feed concentration and vacuum pressure and effects of membrane characteristics including porosity, pore size and thickness on permeate flux were investigated. Moreover, field distributions (velocity, temperature and concentration) and flux along the membrane module were studied. Based on results, increasing feed temperature, porosity and pore size leads to permeate flux enhancement, while increasing vacuum pressure, feed concentration and thickness causes to permeate flux diminution. Furthermore, the simulation validation was performed using the comparison of results with the experimental data. Hence, the model was found to have significant potential for simulating VMD involving different aqueous solutions.