Mass transfer in hollow fiber module for reverse osmosis seawater desalination

With regard to mass transfer in a seawater flow channel of a hollow fiber m odule used for seawater desalination, the seawater flow channel in an infin itesimal space is taken as a model of a flow channel in a circular tube and between similarly parallel flat plates. An analytical solution of velocity distribution and a numerical solution of concentration distribution are obtained from fundamental equations by use of a separation procedure of variables. As a result, the ratio of concentra tion polarization on a membrane surface is determined by salt rejection and a dimensionless volumetric flux of water through the membrane, that is, a product of the volumetric flux of water through the membrane and the half w idth of the flow channel are divided by a diffusion coefficient. It has become clear that under practical operating conditions, the ratio of concentration polarization can be ignored. There is almost no difference b etween a seawater flow channel model with parallel flat plates and another model in the form of a circular tube. On the other hand, the calculated thi ckness of a concentration boundary layer is much larger than the width of t he seawater flow channel in a conventional equation of mass transfer, which is expressed as a function of Reynolds number. It seems that this may be m istaken for a non-uniform flow not related to diffusion resistance.