SHORT AND LONG-TERM FLUX DECLINE ANALYSIS IN ULTRAFILTRATION

Flux decline during stirred UF over a long time of operation can be cl assified into short and long time domains. In the short time, the decl ine in flux is basically osmotic pressure limited and this decline is extremely rapid. The limiting flux for the osmotic pressure controlled domain is obtained by successive substitution technique. This techniq ue includes the variations of properties with concentrations. A modifi ed Sherwood number coorelation for determining the mass transfer coeff icient is proposed for laminar flow in a stirred cell. The long term f lux decline can be modeled semi-empirically by a two parameter model. One of these, the steady state polarized layer resistance, can be corr elated to the operating conditions while the other constant of the mod el is found to be a characteristic of the solute only. The simplistic model developed here to account the flux decline during UF may be usef ul to the process engineers for design purposes.