EXPERIMENTAL INVESTIGATION OF CONVECTIVE HEAT TRANSFER IN A TRANSITIONAL CHANNEL FLOW WITH PERIODIC CAVITY INDUCED ROUGHNESS

An experimental investigation of forced convective heat transfer is reported for a transitional channel flow. One channel wall is formed by repeating surface mounted ribs. Cavities formed in between the ribs provide a surface roughness. The effect of variations in the channel wall-to-wall spacing, the rib-to-rib spacing and flow rate have been studied. The resulting flow and thermal fields, in the vicinity of a single heated rib, are discussed. Investigation of the flow field consisted of a flow visualization study, measurements of axial pressure variation and measurements of the mean and rms axial velocity profile. The disturbance level in the roughness layer, adjacent to the surface, increases with rib-to-rib spacing.;Local measurements of the surface temperature rise, convective heat flux and transverse temperature profile were obtained using a Mach-Zehnder interferometer. Variation of the local conductance with axial postion is similar to that of a laminar smooth wall flow. Transverse temperature profiles display similarity when the transverse coordinate is normalized by the thermal boundary layer thickness. The average convective resistance is well correlated with a Reynolds number based on the rib length using a power law. The effect of the volume average velocity on the average convection rate is dominant; geometry variations produce secondary effects. At small rib-to-rib spacing the convection rate is the same as for a smooth wall transitional flow. At large rib-to-rib spacing a change from a roughness independent to a roughness dependent regime occurs as flow rate increases. In the latter regime the "turbulent" transport is enhanced as increases in the rib-to-rib spacing increase the roughness.