Tung-Wen Cheng

Influence of inclination on gas-sparged cross-flow ultrafiltration through an inorganic tubular membrane

Abstract The effect of membrane inclination on the flux of single-phase or gas–liquid two-phase ultrafiltration in a tubular membrane has been investigated. Experimental result shows that membrane inclination has a significant enhancement on the flux of two-phase ultrafiltration operated at slug flow pattern. As the angle of inclination from the horizontal increases, the flux increases, reaches a maximum, and then decreases. The flux may be enhanced more than 1.5 when the membrane is inclined from 0 to 50°. The flux enhancement due to membrane inclination increases with increasing the gas velocity, the feed concentration, and the transmembrane pressure, while it decreases with increasing the liquid velocity. The optimal inclination angle of the membrane in a slug-flow ultrafiltration is close to 50°. An equation for determining the optimal inclination angle was also proposed in this work.

Effects of gas slugs and inclination angle on the ultrafiltration flux in tubular membrane module

Abstract The permeate fluxes of an inclined gas-slugs ultrafiltration system were measured and discussed under various gas–liquid flow ratios and inclination angles. The experiments were carried out in a tubular ceramic membrane module by using dextran T500 aqueous solution as the tested solution. In the single liquid-phase ultrafiltration system or the gas–liquid two-phase ultrafiltration system with turbulent liquid flow, the variation of inclination angle affects the permeate flux slightly. In the gas–liquid two-phase ultrafiltration system with laminar liquid flow, the permeate flux is enhanced significantly as the inclination of the ultrafiltration column increases up to a certain angle. The optimal inclination angle of the ultrafiltration column is about 53° in present experimental system. The enhancement in flux is due to the combination effects of natural convection and forced convection induced by the slug flow in the inclined tubular membrane.

Analysis of dialysis coupled with ultrafiltration in cross-flow membrane modules

Analytical solution of solute concentration for the systems of dialysis coupled with ultrafiltration in cross-flow membrane modules was obtained by the method of perturbation, and thus separation efficiencies could be calculated for various operating and design conditions. The overall mass transfer coefficient was assumed to be constant and the concentration polarization and pressure drop on both compartments were neglected in solving this problem. Moreover, the mean values of permeation flux and sieving coefficient were taken and were treated as constant. It was found that increasing the flow rate in retentate phase is more beneficial to the mass transfer than increasing in dialysate phase. The performance of dialysis can be improved significantly by the effect of ultrafiltration, especially for the systems with low mass transfer coefficient. The present analysis could be applied to all kinds of configurations, such as parallel-flow, radial-flow and spiral-wound types, but with the limitations of laminar flow and low viscosity and high diffusivity of the fluids.

Filtration characteristics of the rejected-solute layer in dead-end ultrafiltration

The characteristics of the rejected-solute layer of ultrafiltration were investigated in a dead-end experimental apparatus with sudden reduction of filtration area. The aqueous solution of dextran T70 and T500 were ultrafiltrated in the flat membrane module with various inclination angles. The operating parameters of experiments included the inclination angles of the membrane, transmembrane pressures, compositions of solution and the membrane cut-off. Based on the conventional cake filtration theory, the filtration characteristics (the porosity and specific resistance of the rejected-solute layer) can be obtained from the flux data. Experimental results indicates that porosity of the gel-cake layer decreases while the specific resistance increases with the increase in the transmembrane pressure. The mixture solution has a larger specific resistance than a single-solute solution. The filtration under 90° inclination has a larger porosity than that under 0 or 180° inclination, and the operation under 0° inclination has a larger specific resistance of the gel-cake. Using a large molecular weight cut-off (MWCO) membrane will form a more compact gel-cake than that using a small MWCO one.