Membrane Distillation: Parametric Studies and Numerical Simulations for Hollow Fiber and Flat Sheet Membranes

Abstract

Water scarcity is among the most serious, long-term challenges in the world. To an ever increasing degree, sustainable water supply depends on the utilization of water of impaired initial quality. This is particularly true in developing nations and in water-stressed areas such as the American Southwest. Water of impaired quality could be water of high salinity such as brackish groundwater. Traditionally, reverse osmosis (RO) would be chosen to desalinate the brackish groundwater, since RO costs are competitive with those of thermal desalination, even for seawater applications. However, both conventional thermal distillation and RO are energy intensive, complex processes that discourage decentralized or rural implementation. In addition, both technologies require enhanced expertise for operation and maintenance, and are susceptible to scaling and fouling unless extensive feed pretreatment is employed. Membrane distillation (MD), driven by vapor pressure gradients, can potentially overcome many of these drawbacks. MD can operate using low-grade, sub-boiling temperature heat sources. When it is driven by solar energy it does not require highly concentrating collection devices, non-aqueous working fluids, or complex temperature control systems, nor does it require extensive operational expertise. Membrane Distillation (MD) applications, background and modeling efforts are discussed in the first part of this dissertation. Two main studies are presented in this document: Firstly, Sweeping Gas Membrane Distillation (SGMD) through a hollow fiber membrane was studied both experimentally and modeled mathematically to describe performance of SGMD and extend results to predict membrane module efficiency and secondly, SGMD through a flat sheet MD module to study the effect of membrane characteristics in combination with operational variables. A final study was conducted to examine the effect of mesh spacer insertion in flat sheet membrane module on the permeate water production.