Experimental investigation of flow and heat transfer in a rectangular channel with 45° angled ribs on one/two walls

The flow and heat transfer characteristics in a rectangular channel (aspect ratio AR=5) with angled rib turbulators, inclined at 45 deg, have been investigated. The angled ribs were attached, with parallel orientations, on one or two surfaces of the channel. The ratio of rib height to hydraulic diameter (e/D) was 0.09, while the rib pitch-to-height ratio (P/e) was 10. Experiments were carried out using air as the convective fluid, with the Reynolds number Re=29000 and periodic fully developed conditions. The flow patterns were investigated by using laser-Doppler velocimetry (LDV), while the local heat transfer coefficients were provided by liquid crystal (LC) thermography. Inclined ribs are responsible for two-cell secondary flow when installed on two opposite walls of the channel and for one-cell secondary flow when placed on one wall only. The secondary flow brings relatively cold core fluid towards the rib leading end regions and warm fluid towards the opposite rib trailing regions, causing marked spanwise variations in the local heat transfer coefficient.