Random Surface Roughness Effect on Microtube Heat Transfer

Abstract

We propose a novel bottom-up approach to generate a rough microtube surface. This approach starts from four corner points with two defined coordinates and roughness height created by a Gaussian number generator, and uses a bi-cubic Coons patch repeatedly to form the curved surface. A computational fluid dynamics solver is used to isolate the roughness effect and solve the three-dimensional N-S equations for the flow through the generated rough microtubes with diameter D = 50μm and length L = 100μm. The boundary conditions are carefully defined for results comparison between smooth and rough microtubes. It is found that when the mean diameter of the rough microtube is used as the hydraulic diameter, the roughness has little effect on the averaged Nusselt number and it still can be predicted by the conventional theory because the effects of peaks and valleys are counteracted for the whole microtube. The local Nusselt numbers along the microtube randomly distribute below the theoretical value with a very small deviation.