Laminar forced convection characteristics in a round microchannel with shape uncertainty: effect of wall slip

TL;DR

This study investigates how shape uncertainties in microchannels affect laminar forced convection, revealing that roughness generally decreases heat transfer efficiency while increasing flow resistance, especially at small scales with wall slip.

Contribution

It provides a detailed analysis of the sensitivity of heat and fluid flow to shape variations in microchannels considering wall slip effects, using a large set of randomized geometries.

Findings

Roughness tends to lower Nusselt number on average.

Roughness increases Fanning friction factor.

Wall slip influences heat transfer and flow resistance.

Abstract

The shape of a microchannel cross-section is usually affected by a significant uncertainty due to the small hydraulic diameter. Such an uncertainty is indeed present at any scale, but is amplified in smaller scales, becoming significantly important when the hydraulic diameter is smaller than some tenth micrometers. In this scenario, this paper is focused on analyzing the sensitivity of the heat and fluid flow characteristics with respect to the channel shape, considering a random modifications in the channel cross section. Forced convection in a fully developed regime with a wall slip is considered, and the analysis includes the evaluation of the Fanning friction factor and of the Nusselt number for the H1 thermal boundary condition, considering different slip-flow configurations, as dictated by the slip-length parameter. The heat and fluid flow problem is solved for one thousand randomly generated channel geometries, based on a circular microchannel which is allowed to have its boundary points move within 10\% of its nominal diameter. The calculated data for $f \Re$ and $\Nu$ are then analyzed, and compared with the nominal values (obtained for smooth channels). The results show that, on an average basis, the roughness effect has a tendency to reduce the Nusselt number while increasing the friction factor, however, with a small number of exceptions.