The expression of mass transfer coefficient is derived from first principles for the turbulent non-Newtonian fluid flow in the membrane modules. The effects of suction are incorporated in the mass transfer coefficient from a theoretical basis. The analysis is carried out for a power law fluid, the common rheology for fruit juices and other food products. The analysis shows that there is significant effect of suction on mass transfer coefficient. The effects of the operating conditions, e.g., Reynolds number, permeate flux and the rheological nature of the fluid (pseudoplastic or dilatant) on the mass transfer coefficient are also investigated. Both rectangular thin channel and tubular modules are considered. (C) 2004 Elsevier Ltd. All rights reserved.