The predicting equation for the permeate flux of membrane ultrafiltration in hollow-fiber modules, was derived from the complete momentum balance coupled with the application of hyperbolic-tangent model. The correlation predictions obtained in present modeling study are based on the consideration of the effect of the loss of momentum transfer due to convection. It is found that the hyperbolic-tangent model analysis for permeate flux confirms well with the ultrafiltration of polyvinyl alcohol aqueous solution in hollow fiber modules.