Direct contact membrane distillation: The role of membrane porosity

Isam Janajreh, Khadije El Kadi, Noora Al Hammadie, Raed Hashaikeh

Research output: Contribution to journalArticlepeer-review

Abstract

Direct contact membrane distillation (DCMD) is pursued as low energy thermally driven process. Its basic configuration consists of two chambers one for the hot brine feed and second for the colder fresh permeate separated by a thin-porous-hydrophobic membrane of low thermal conductivity. The process involves brine evaporation that localized at the hot membrane surface, vapor transport through the thin porous membrane and condensation at the permeate membrane surface side. A sustaining temperature difference across the membrane ensures the driving process pressure. In this work a validated high fidelity model is developed to quantitatively assess the DCMD performance that address the influence of the porosity for homogenous and composite membrane. The flow is governed by the Navier-Stokes of none-isothermal that thermally coupled with the hydrophobic porous membrane consist of a single PVDF layer and a triplet layered membrane in which a stiffer layer SiO is sandwiched in between the PVDF to improve membrane post-treatment. The model was tested2 and run at fixed salinity value for the brine of 4% and inlet temperate of 75˚C under different porosity and membrane composite configurations. Results reveals a pronounced influence of the porosity seen by temperature polarization (TPC), mass and heat flux across the membrane, as well as thermal efficiency metrics. Specifically, an increase or decrease in porosity from the baseline 85% by 5 and 10 points lead to and increase/decrease in the mass flux and the thermal efficiency by 11–12% and 22–25%, respectively. The introduction of a sandwiched silicon oxide layer while preserved the same trend and relative values it, however, drastically reduced the mass flux and efficiency due to over all penalty in the membrane conductivity. This suggests that while inclusion of functional material could improve membrane reliability and post treatment one needs to use these materials at higher porosity than the original membrane to compensate for their added conductivity.

Original languageEnglish (US)
Pages (from-to)258-267
Number of pages10
JournalDesalination and Water Treatment
Volume100
DOIs
StatePublished - Dec 2017

Keywords

  • Composite membrane
  • Membrane distillation
  • Membraneporosity
  • Temperature polarization (TPC)
  • Thermal efficiency

ASJC Scopus subject areas

  • Water Science and Technology
  • Ocean Engineering
  • Pollution

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