Effect of rib spacing on heat transfer in rectangular channels with 45 deg ribs on one wall

An experimental investigation of heat transfer in a rectangular channel with angled rib turbulators, inclined at 45 deg, is presented. The angled ribs were deployed with parallel orientations on one wall of the channel. The aim of the work was to study the effect of the rib spacing on the thermal performance of the ribbed channel. Experiments were based on the use of heating foils and the steady-state, liquid crystal thermography. From the processing of liquid crystal images, the maps of local heat transfer coefficient (and local Nusselt number) have been reconstructed. The thermal performance of each ribbed channel is identified by the average Nusselt number and by the friction factor obtained from the measured pressure drop across the ribbed test section. The optimal rib pitch-to-height ratio giving the best heat transfer performance was identified, for the explored range of Reynolds number, under the constraints of constant mass flow rate or pumping power.