Tubular ceramic membranes with many, small-diameter feed flow channels have the advantage of being less costly per unit membrane area. For this reason, membranes with many small channels are often favored over those with fewer larger channels. We have theoretically studied how the diameter of the feed flow channels influences the frictional pressure drop, the membrane performance (flux and retention) and the process cost by performing basic pressure drop calculations and using experimental data from bench-scale experiments. The investigation was carried out on a model microfiltration process consisting of the separation of yeast cells from polyethylene glycol (PEG) macromolecules. For a membrane with 2.5 mm channels the average flux and PEG retention were 112 L/m(2)h and 22%, respectively, differing significantly from a membrane with 6.0 mm channel diameter (131 L/m(2)h, 17%), under the same hydrodynamic conditions. The choice of channel diameter also has a considerable impact on the process cost. While the costs were similar for membranes with 6.0 and 3.8 mm diameter channels, they were about 55% higher using a membrane with 2.5 mm channels. This high cost was mainly attributed to the high frictional pressure drop along the membrane, which increases the energy required for pumping. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.