Modelling of roughness effects on heat transfer in thermally fully-developed laminar flows through microchannels

In this paper, roughness was modelled as a pattern of parallelepipedic elements of height k periodically distributed on the plane walls of a microchannel of height H and of infinite span. Two different approaches were used to predict the influence of roughness on heat transfer in laminar flows through this microchannel. Three-dimensional numerical simulations were conducted in a computational domain based on the wavelength lambda. A one-dimensional model (RLM model) was also developed on the basis of a discrete-element approach and the volume averaging technique. The numerical simulations and the rough-layer model agree to show that the Poiseuille number Po and the Nusselt number Nu increase with the relative roughness. The RLM model shows that the roughness effect may be interpreted by using effective roughness heights k(eff) and k(eff theta) for predicting Po and Nu respectively. k(eff) and k(eff theta) depend on two dimensionless local parameters: the porosity of the rough-layer and the roughness height normalized with the distance between the rough elements. The present results show that roughness increases the friction factor more than the heat transfer coefficient (performance evaluation criteria < 1), for a relative roughness height expected in the fabrication of microchannels (k/(H/2) < 0.46) or k/D-h < 0.11). (C) 2009 Elsevier Masson SAS. All rights reserved.