Convection forcée de liquides en régime laminaire dans des micro-canaux en silicium

Abstract

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. 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 more appropriate control of the channels’ cross-section and the increase in the reliability/accuracy of the recent experimental data. In this paper the conventional theory is used to calculate numerically the Poiseuille numbers and the Nusselt numbers for trapezoidal and rectangular microchannels in which a liquid flows in laminar regime. It is evidenced the role of the cross-section geometry on the pressure drops and the local values of the convective heat transfer coefficients by taking into account the viscous dissipation inside the fluid. The numerical results presented in this paper have evidenced that the conventional theory is able to explain the experimental results obtained for trapezoidal microchannels in terms of friction factors for microchannels with hydraulic diameters greater than 30 µm. It has been demonstrated that for liquid flows, if the microchannel hydraulic diameter becomes less than 50 µm, viscous dissipation effects cannot be ignored for large Reynolds numbers.