Exploration of the effect of surface roughness on heat transfer in microscale liquid flow

As technology provides smaller devices with greater heat dissipation needs, microfludic systems become essential. The scale of device architecture causes concerns to arise that were previously not an issue. The results of manufacturing processes, such as roughness structures on machined surfaces, now play a significant role in transport phenomena. This study takes an analytical and experimental approach to understanding the fundamental heat transfer process in rectangular channels with artificially roughened walls. Steady, incompressible, fully developed liquid flow is modeled with lubrication theory to develop an expression for the fully developed Nusselt number. The heat transfer performance of the small aspect ratio rectangular channels with two wall heating under the H2 boundary condition is experimentally investigated. A constant wall heat flux is applied at opposing long walls. Four different structured roughness geometries are investigated along with smooth channels as the heated walls. In total, hydraulic diameters ranged from Dh = 183mum to Dh = 1698mu m and were tested over a Reynolds number range of 45 to 600. The pitch to height ratio of the sinusoidal roughness surfaces covered the ranged of 2:6 to 10:6. The resulting relative roughness was 2:17% to 16:53%. Fully developed Nusselt was found to lie below classic theory. Sinusoidal roughness geometries were found not to provide heat transfer enhancement over smooth channel walls.