Influence of streamwise pitch on the local heat transfer characteristics for in-line arrays of circular jets with crossflow of spent air in one direction

Influence of the streamwise pitch on local heat transfer distribution due to a rectangular in-line array of circular air jets of length-to-diameter ratio (l/d) of 1.0 is studied experimentally. The flow, after the impingement, is constrained to exit in one direction. Mean jet Reynolds number is varied from 3000 to 10000 and jet-to-plate spacing from d to 3d. Streamwise jet-to-jet distances of 3d, 4d and 5d and a constant spanwise pitch of 4d are considered. A flat target surface is made of thin stainless steel metal foil. The local temperature distribution on a target plate is measured using thermal infrared camera. The jet exit pressures are measured to estimate the cross-flow velocities and individual jet velocities. The streamwise distribution of the jet-flow and the cross-flow is least influenced by the streamwise pitch variation for the range of parameters investigated. Heat transfer characteristics are explained partially on the basis of flow distribution. The cooling performance, based on strip averaged Nusselt number per unit mass flow rate of coolant per unit area of cooled surface, deteriorates for lower streamwise pitch and higher jet-to-plate distance.