In this paper an attempt has been made to review the literature regarding heat transfer and pressure drop in one- and two-phase flow in microchannels. The emphasis has been on reports presented during the last few years. For single phase flow, channels with hydraulic diameters less than 1 mm have been considered. In two-phase flow very little information is available for such small channels. Also, for two-phase flow, deviations from large-tube behavior start at diameters of a few millimeters. For these reasons a slightly larger diameter range has been considered in this case.
As a conclusion it could be stated that the understanding of flow in microchannels is increasing steadily, but that there are still many questions to be answered concerning the reasons for deviations from classical theory developed for larger channels.