A detailed modeling, analysis and simulation of an out-in configuration vacuum membrane distillation (vmd) process

Abstract

A detailed rigorous theoretical model has been developed to predict the transmembrane flux of a shell-and-tube type vacuum membrane distillation (VMD) module for seawater desalination. There are primarily two modes of operation to carry out VMD: lumen-side feed (in-out configuration) and shell-side feed (out-in configuration). In this study, detailed mathematical formulations are derived, not for in-out configuration since it has been observed to be restricted by operational constraints such as crystallization in the lumen side of the hollow fiber at high seawater concentrations, but for outin configuration commonly used in seawater desalination applications. For the out-in configuration VMD module, in spite of the much lower viscosity of water vapor than liquid phase, the pressure build-up of water vapor in the lumen should not be overlooked as the pressure build-up directly reduces the driving force for vapor permeation through the membrane pores. Experimental results and model predictions for mean permeate flux are compared and shown to be in good agreement. The property variation of feed and permeate sides along the axial direction is also examined. Further, the influences of operating parameters (feed temperature and flow rate, hollow-fiber length) on the permeate flux are evaluated, and the pressure build-up of the water vapor in the lumen side is also investigated.