Dynamic performance of vacuum membrane distillation system

Abstract

The aim of this work was the development of a numerical methodology to simulate and study the dynamic behavior of vacuum membrane distillation (VMD) system. A time-dependent one-dimensional finite difference numerical model is developed to study the flow as well as thermal regimes and the dynamic operational performance of VMD under stepped flow disturbance function in the hot channel. The study simulates the process parameters including mass flow rates, temperatures, vapor pressures, and concentration distributions for the hot feed channels along the flat-plate membrane length with transmembrane flux. The developed dynamic tool predicts the hydrodynamic behaviors and thermal characteristics of the very thin channels of VMD module. A rectangular pulse disturbance function is applied to rise up the inlet hot mass flow rate from steady state (SS) value of 1 to 1.34 kg/s for 60 s. The model ran for 3 min, which included the 60 s of applied dynamic disturbance; it started at the 10th s and finished at the 70th s. The results show that the probability of the pressure rise and the salt precipitation (scaling problem) will appear on the second half of the membrane length more than on the first half. The hydrodynamic influence of the flow conditions on the permeate flux appears to be more significant at the feed side of the VMD module fillet.