Laminar forced convection of liquid flows through silicon microchannels

Many experimental works which appeared in the last decade in the open literature concluded that for channel having a hydraulic diameter less than 1 mm the conventional theory can no longer be considered as able to predict the pressure drop and convective heat transfer coefficients. This conclusion seemed valid for both gas and liquid flows. Sometimes the authors justified this conclusion by invoking new micro-effects, e.g. electrostatic interaction between the fluid and the walls and so on. From a chronological analysis of these experimental results, it is possible to remark that the observed deviations from the prediction of the conventional theory are decreasing. This fact can be explained by considering the dramatic improvement in the microfabrication techniques with the consequent reduction of the influence of surface roughness of the, a more appropriate control of the channels’ cross-section and the increase in the reliability/accuracy of the more recent experimental data published in literature. In this paper the conventional theory is used to calculate the main integral flow parameters, to predict the critical Reynolds numbers associated with the laminar-to-turbulent transition and the Nusselt numbers for silicon <100> and <110> microchannels. It will be demonstrated that many among experimental results which appeared in the open literature for liquid flows through silicon microchannels can be explained by using the conventional theory, without invoking any particular micro-effects.