Experimental and theoretical investigations on the influence of spacer on the DCMD process performance

Abstract

In this study, the experimental and theoretical studies have been carried out to achieve a more comprehensive and systematic understandings on the fundamentals in heat and mass transfer through a commercial flat sheet composite membrane that employs different types of spacers in bulk feed and permeate flow channels. The commercial composite membrane used is comprised of an active layer of polytetrafluoroethylene (PTFE) and a scrim-backing support layer of polypropylene (PP), and its performance has been tested in the DCMD process. The different types of polypropylene and nylon mesh spacers have been used at both sides of the composite membrane as a support and turbulence promoter. In DCMD process the water vapor passes through the dry membrane pores, driven by the vapor partial pressure difference imposed between the liquid–vapor interfaces. The mass transport through the composite membrane can be described by two individual transfer paths: (i) polytetrafluoroethylene active layer not covered by polypropylene scrim support layer at the permeate side (i.e., effective open area for diffusion) and (ii) composite polytetrafluoroethylene active and polypropylene support layers. The influence of the spacers on the permeate flux enhancement in DCMD process with a PTFE/PP composite membrane has been examined experimentally and theoretically. The heat transfer coefficients are evaluated and correlated with the spacer geometries, hydrodynamic angle and voidage.