Local heat transfer characteristics of circular multiple air jet impinging on a semicircular concave surface

The local heat transfer characteristics of circular multiple air jet impingement on semicircular concave surface were studied experimentally. For constant Reynolds number (Re = 9,000), the effect of jet to concave surface spacing (z/d = 1, 4.2, 6), ratio of curvature (D/d = 4.28, 6, 8.6), jet-to-jet spacing (s/d = 2.4, 4, 5.6), and number of jets were considered. The local heat transfer characteristics were determined by using infrared thermal camera and thin foil method. Lower curvature value ratio (D/d = 4.28) resulted higher average heat transfer coefficient due to broader spread of heat transfer distribution, whereas higher curvature ratio (D/d = 8.6) resulted in lower average heat transfer coefficient due to steeper heat transfer distribution in the stagnation area. At lower D/d, z/d, and s/d with seven jet configuration, the heat transfer coefficients were found effective as compared to other configurations due to broad heat transfer distribution and less interaction between the jets. At given D/d and s/d configuration, the stagnation Nu at theta = 0 degrees do not coincide with jet hole center axis and this shift is more pronounced at higher z/d value. This could be due to additional push before jet impinging on concave surface. The secondary peaks were observed between two neighboring stagnation regions in Nu distribution along the center longitudinal line for lower z/d and higher s/d values. This resulted due to upwash that was obtained from jet interactions related to collisions with the wall jets. The correlations of stagnation line average Nu and overall average Nu were obtained. The coefficient of variance of local heat transfer coefficient for each configuration was determined, and correlation was proposed to analyze the degree of non-uniformity.