The effects of viscous dissipation on the temperature field and ultimately on the friction factor have been investigated using dimensional analysis and experimentally validated computer simulations. Three common working fluids, i.e., water, methanol and iso-propanol, in different conduit geometries were considered. It turns out that for microconduits, viscous dissipation is a strong function of the channel aspect ratio, Reynolds number, Eckert number, Prandtl number and conduit hydraulic diameter. Thus, ignoring viscous dissipation could affect accurate flow simulations and measurements in microconduits. (C) 2004 Elsevier Ltd. All rights reserved.