The main objective of this work is to introduce a length correction Factor, based oil CFD simulation results, in order to extend the method for taking into account the surface roughness effects ill the calculation of laminar flow through rough microchannels described in [J.R. Valdes, M.J. Miana, T. Putz, Numerical investigation of the influence of roughness On the laminar incompressible fluid flow through annular microchannels, Int. J. Heat Mass Transfer 50 (2007) 1865-1878], to surface roughness values much larger than the ones considered in the previous study. The method proposed in Valdes et al. (2007) consisted in building an equivalent smooth channel with the same flow resistance as the rough one. As in this case, the new method is validated with results of CFD simulations of microchannels with different roughness values. (C) 2008 Elsevier Ltd. All rights reserved.