PREDICTION OF MASS-TRANSFER COEFFICIENT WITH SUCTION IN THE APPLICATIONS OF REVERSE-OSMOSIS AND ULTRAFILTRATION

Sherwood-number relations for prediction of the mass-transfer coeffici ent for developing concentration boundary-layer have been obtained for laminar flow-regime from first principles. The common flow-modules, n amely, rectangular channel, tubular and radial cross-flow are consider ed. The relationships developed include the effect of suction through the membrane. Relevant relations for estimation of mass-transfer coeff icient for cross-flow reverse osmosis and ultrafiltration are formulat ed. The Sherwood-number relations developed are compared with the stan dard correlations to quantify the effect of the suction. The proposed Sherwood relations are used in conjunction with the osmotic-pressure m odel to predict the permeate flux in reverse osmosis and osmotic-press ure governed ultrafiltration.