The modified correlation equation for predicting the permeate flux of membrane ultrafiltration (UF) in hollow-fiber modules was derived from the complete momentum balance coupled with the application of exponential model. The correlation predictions obtained in present study are more accurate than those obtained in the previous works, in which the momentum balance was taken inaccurately by simply applying Hagen-Poiseuille theory without the consideration of the effect of permeate flux loss, as well as the effect of the loss of momentum transfer due to convection. on overall momentum balance. (C) 2008 Elsevier B.V. All rights reserved.