In this work, a commercial computational fluid dynamics code (CFD), Fluent, was used to analyze the design of a filterpress reactor working under laminar flow (300 < Re < 2000) and transition (2000 < Re < 3000) regimes. The reactor is a rectangular channel (0. 1 m length x0.05 m width x0.01 m depth) made of acrylic. Several velocity flow profiles have been obtained as a function of the channel length and width. For the laminar and transition flow regimes, Re number was evaluated as a function of channel length and width. At the center of the channel, Re number was evaluated as a function of its length. It was found that Re number is quasi-constant after short distances from the entrance, indicating a developed flow. A three-dimensional reticulated vitreous carbon (RVC) electrode (60 pores per inch, 0.0 m x 0.05m x 0.01m) was fitted at the center of the channel and was found that experimental mass transfer coefficient (k(Fe(CN)6)(3-)), obtained from different flow velocities, obeys the empirical correlation k(m)Ae = av(b) (where k(m) is the mass transfer coefficient, v is the flow velocity, A(e) is the specific surface area of the electrode, a and b are constants) under the flow regime studied. Other velocities and geometries are discussed in the work. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.