Variable property effects in single-phase incompressible flows through microchannels

In a systematic approach we address the question of how important variable property effects are for flows in micro-sized channels. Due to heat transfer, the temperature dependence of fluid properties like viscosity and thermal conductivity results in deviations in a solution which accounts for that dependence compared to a solution only considering constant fluid properties. Compared to flows through macro-sized geometries, it turns out that two distinct scaling effects lead to a strong influence of variable fluid properties in micro-sized channels; Reynolds numbers are Re=O(1) and not large, and axial temperature gradients are no longer small. These scaling effects can be identified after the basic equations are nondimensionalized properly. Examples are given in which Nusselt numbers differ by up to 30% depending on how the property behaviour is accounted for.