For the materials in modern gas turbines to survive, a considerable amount of cooling is required. In cases where large amounts of heat need to be removed, impingement cooling with its high heat transfer coefficients may be a good alternative. The possibilities of enhancing impingement cooling by introducing surface enlarging/turbulence enhancing elements are examined experimentally in this work. A technique using thin foil heaters combined with an infrared camera is used. Local temperature distribution on the target plate is measured, enabeling to separately evaluate the Nusselt number enhancement for different areas. Experiments are conducted for four different area enlarging geometries: triangle, wing, cylinder and dashed rib all made from aluminum. Comparison between each area enlarged surface and a flat plate is made in terms of Nusselt number and also pumping power in order to maximize the cooling efficiency. Overall Nusselt number enhancement factors compared to impingement on a flat plate show values of 1 to 1.3, the trend decreasing with increased jet-to-plate distance and Reynolds number. When normalizing by the spent pumping power the enhancement factors drop to 0.4 to 1.2 compared to impingement on a smooth plate. The best results were achieved with die rib geometry and when not using a too large value of enlarger height compared to jet-to-plate distance. Row-wise evaluation of Nusselt number enhancement shows an increased enhancement factor with row number and therefore crossflow ratio (Gc/Gj). The infrared camera pictures reveal that the enhancement is found in three different areas, on the enlarger base area, the area just downstream the enlarger and in diagonal streaks with increased turbulence generated by the enlargers. Tests using an enlarger material with heat conductivity scaled to represent actual gas turbine conditions show that only the enlarger base area is affected when decreasing the enlarger heat conductivity. The result is a small decrease in total Nusselt number enhancement.

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