Numerical and Experimental Investigation of Direct Contact Membrane Distillation (DCMD)

Abstract

Direct contact membrane distillation (DCMD) qualifies to be an emerging water separation technology that acquires low-grade energy requirement for several applications such as desalination. The system incorporates the integration of two parallel channels comprising saline water approximately at 3.5% salinity and fresh water flowing at different inlet temperatures in an adjacent configuration. The flows are in direct contact with a thin porous hydrophobic membrane polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) at the respective sides. The temperature gradient induces a pressure difference across the membrane, triggering partial vaporization of water film at the feed-side. The remaining pressure gradient facilitates the vapor transport through the membrane pores via combined mechanisms (Pouiselle, Diffusion, Knudsen) leading to condensation at the permeate side where the flux is collected. DCMD suffers low efficiency in comparison to other technologies such as RO, MSF, solar still and other thermal desalination, thus demoting it to be economically unfeasible and drawing limitations towards commercialization. This thesis aims to fulfill two main goals, firstly to establish a solid numerical investigation to seek and identify the main pronouncing parameters influencing the DCMD productivity and thus quantify them. This lead to high fidelity model development of conjugated heat flow within the framework of Ansys Fluent and Matlab. The model considered several inlet conditions, parallel and counter flow configurations, geometrical assessment and other complementing studies with the implementation of the suitable transport mechanisms, boundary and flow conditions. The second aim was to bridge the gap between theoretical and practical analysis to a broad application of an experimental test unit in order to validate and present a robust view. The setup involved the combination of PVDF membrane and a DCMD cell designed by the authors. The exploration focused primarily on the ability of the arrangement to desalinate seawater, produce flux, and thus qualitatively comprehend the validity of the system in comparison with simulation models. Results were in line with numerical simulation and other published literature on the low flux and process metrics. Therefore, qualifying the eligibility of this technology for further potential advances in terms of high flow metrics.

Date of Award	May 2015
Original language	American English
Supervisor	Isam Janajreh (Supervisor)