HYDRODYNAMIC MODEL AND EXPERIMENTS FOR CROSSFLOW MICROFILTRATION

Crossflow microfiltration, in which a suspension is passed through a pressurized open-ended tube or channel having microporous membrane walls, is an effective means of filtering fine particles from a liquid and is finding increasing application in separations involving microbial suspensions and products. The particles, which are carried toward the walls with the filtrate cross-flow, form a thin cake layer on the membrane surface which does not accumulate substantially but is rather swept along the channel by the tangential flow of suspension. This paper presents a stratified-flow model of this phenomenon which predicts the steady-state permeation flux, and the velocity, pressure, and concentrated particle layer thickness profiles, as functions of the system parameters. In addition, the results of laboratory experiments which used a crossflow microfiltration channel with glass sides are reported. The measured steady-state thickness of the cake layer as a function of distance from the channel entrance shows good agreement with the theory, except for the case of a relatively thick layer when it is believed that a stagnant sublayer had formed beneath the flowing cake layer.