Enhancement of Impingement Heat Transfer With the Crossflow Normal to Ribs and Pins Between Each Row of Holes

Impingement heat transfer investigations with obstacle (fins) on the target surface were carried out with the obstacles aligned normal to the cross-flow. Conjugate heat transfer (CHT) computational fluid dynamics (CFD) analysis were used for the geometries previously been investigated experimentally. A 10 × 10 row of impingement jet holes or hole density, n, of 4306 m−2 with ten rows of holes in the cross-flow direction was used. The impingement hole pitch X to diameter D, X/D, and gap Z to diameter, Z/D, ratios were kept constant at 4.66 and 3.06 for X, D and Z of 15.24, 3.27 and 10.00 mm, respectively. Nimonic 75 test walls were used with a thickness of 6.35 mm. Two different shaped obstacles of the same flow blockage were investigated: a continuous rectangular ribbed wall of 4.5 mm height, H, and 3.0 mm thick and 8 mm high rectangular pin-fins that were 8.6 mm wide and 3.0 mm thick. The obstacles were equally spaced on the centre-line between each row of impingement jets and aligned normal to the cross-flow. The two obstacles had height to diameter ratios, H/D, of 1.38 and 2.45, respectively. Comparison of the predictions and experimental results were made for the flow pressure loss, ΔP/P, and the surface average heat transfer coefficient (HTC), h. The computations were carried out for air coolant mass flux, G, of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss and surface average HTC for all the predicted G showed reasonable agreement with the experimental results, but the predictions for surface averaged h were below the measured values by 5–10%. The predictions showed that the main effect of the ribs and pins was to increase the pressure loss, which led to an increased flow maldistribution between the ten rows of holes. This led to lower heat transfer over the first 5 holes and higher heat transfer over the last 3 holes and the net result was little benefit of either obstacle relative to a smooth wall. The results were significantly worse than the same obstacles aligned for co-flow, where the flow maldistribution changes were lower and there was a net benefit of the obstacles on the surface averaged heat transfer coefficient.