Non-Isothermal Pervaporation

Pervaporation includes a phase change as compounds are transported from the liquid feed to the vapour permeate. This vaporization involves a consumption of energy and thus a decrease in the mixture temperature on the membrane feed-side. This temperature can be seen as a temperature difference between the feed and the retentate, as well as between the feed and permeate streams. Usually, this thermal effect is assumed to have a little effect on mass transfer, however recent studies have bee pointed out that it can have substantial influence in certain systems.

In order to study the heat transfer problem in pervaporation we have developed a two-dimensional numerical model, which includes the continuity equation, the Navier-Stokes equation, and the energy and convection-diffusion equations, respectively, for the temperature and concentration fields. The model equations were solved simultaneously for a specific geometry and initial and boundary conditions. In this paper we report on simulations with binary-mixtures cases, which include the dehydration of ethanol and the removal of organics from water. Results showed that the temperature variation can be significant near the membrane surface. As a result, there is an accompanying reduction in the mass fluxes of the components through the membrane, relative to the usual isothermal assumption.

The present modeling scheme is presently being applied to tubular pervaporation geometry and to multicomponent pervaporation systems.

Schematic illustration of a rectangular pervaporation channel geometry.

Axial variation of wate concentration along the pervaporation channel for ethanol dehydration. Feed composition = 95.6% ethanol (w/w). Feed temperature = 333 K; Permeate temperature = 293 K; Re = 513; Sc = 164; Pr = 8.2; H/L = 0.01.

Axial variation of the local Sherwood number for the pervaporation of TCE-water at different feed temperatures. Feed = 0.024 % (w/w) TCE, permeate temperature = 293 K; Feed temperatures= 298-348 K, H/L = 0.01.

Reference:

Juan P.G.Villaluenga and Yoram Cohen, "Numerical Model of Non-Isothermal Pervaporation in a Rectangular Channel," Journal of Membrane Science, submitted (2004).

Last update:

10/24/2004