Numerical study on desalinated water flux from NACL solution using hollow fiber type DCMD module

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.

The direct contact membrane distillation process is used for water desalination. DCMD is a thermally driven separation process, in which only vapor molecules transfer through a microporous hydrophobic membrane. The driving force in the DCMD process is the vapor pressure difference induced by the temperature difference across the hydrophobic membrane. In this study, the one-dimensional based model is developed for predicting the performance of the seawater desalination to produce fresh water for hollow fiber type DCMD module. The mass, energy and momentum balance equations are coupled to determine the concentration of NaCl, the temperature and velocity distribution of the feed and permeate side along the module length, and productivity of fresh water in the DCMD process. The KMPT model is used to calculate the mass transfer at the membrane surface. The mathematical and kinetics models used in this study are validated in comparison of the present simulation results with previous data given in the literature. The simulation results are in good agreement with the data in the literature. The performance of pure water production rate with respect to the membrane distillation coefficient is compared with the previously reported data. The numerical analysis is performed on a DCMD module using hollow fiber type PVDF membrane with a pore size of 0.22 μm. Feed solutions are aqueous NaCl solution. The values of the parameters considered in this work are: feed temperature, 40-70 ; feed velocity, 0.472m/s to 0.55m/℃ s; mass fraction of salt, 0.025-0.05; cold permeate temperature, 17-45℃ and the velocity of the permeate side are 0.3 m/s. It is found that the production rate of fresh water increases with feed temperature and velocity, but decreases with feed concentration.