Temperature polarization in membrane distillation of water using a porous hydrophobic membrane

Abstract

The rate of water transport across porous membranes with a hydrophobic matrix (porosity E = 0.5; characteristic length of voids < = 150 nm; thickness 6 = 30 vm) caused by a temperature difference between the bulk phases is studied. The voids of the membrane are filled with water vapour. The effective temperature difference (T'-T") across the membrane is smaller than the temperature difference (T'-T") between the bulk phases ("temperature polarization") caused by heat conduction and by heat flow associated with the water transport. An experimental method is described and tested to determine the temperature polarization coefficient r ( = (7'-T")/(T'-T") for a given experimental situation. The phenomenological transport coefficient of the membrane for water vapour has to be known from independent experiments. This method is a simple alternative to the method developed by Schofield et al. (J. Membrane Sci. 33, 299 (1987)). The dominating factor determining the temperature polarization coefficient is the value of the thickness of the two boundary layer of heat conduction at the interfaces of the membrane.

Review and Analysis of Heat Transfer in Spacer-Filled Channels of Membrane Distillation Systems

“…Nu = 0.664 Re 0.5 Pr 0.333 (A7) Laminar, 1 < Pr < 10, flat-sheet, spacer not inducing change of flow direction [80,96,110] Nu = 0.664Re 0.5 Pr 0.333 (d h /L) 0.5 (A8) Laminar, flat-sheet [13,39] Nu = 0.644 f S Re 0.5 Pr 0.333 (2d h /l S ) 0.5 (A9)…”

Fouling Mitigation in Membrane Distillation Using Pulsation Flow Technique

“…Many scientists have predicted temperature polarization, maybe in light of the experimental study in [40] where a series of electrical sensors were used to predict the experimental and theoretical temperature polarization of DCMD. Besides that, the majority of them demonstrated that the bulk feed and permeate solutions' temperatures (T f and T p ) varied from one another [24,41]. The driving force, or the vapor pressure difference (P f − P p ), as well as the permeate flux through MD membranes, are both decreased as a result of the permeate side's increased partial pressure [24,41].…”

“…Besides that, the majority of them demonstrated that the bulk feed and permeate solutions' temperatures (T f and T p ) varied from one another [24,41]. The driving force, or the vapor pressure difference (P f − P p ), as well as the permeate flux through MD membranes, are both decreased as a result of the permeate side's increased partial pressure [24,41]. Because it is in equilibrium with the liquid phase, a lower temperature on the feed side causes the partial vapor pressure to decrease, while a higher temperature on the permeate side causes the partial pressure to increase.…”

Temperature Polarization Coefficients in Membrane Distillation

“…The importance of this polarization phenomenon in thermal osmosis has been analyzed by Bellucci (3), but it is frequently ignored when analyzing the distillation process using membranes. Nevertheless, a number of studies have appeared recently in the membrane distillation literature with the main purpose of examining the influence of temperature polarization on membrane distillation performance (4)(5)(6)(7)(8)(9)(10). In each of these studies the authors showed that temperature polarization can have a significant effect on the flux.…”