Effects of Jet-To-Target Plate Distance and Reynolds Number on Jet Array Impingement Heat Transfer

Data which illustrate the effects of jet-to-target plate distance and Reynolds number on the heat transfer from an array of jets impinging on a flat plate are presented. Considered are Reynolds numbers Re_j ranging from 8200 to 52,000 with isentropic jet Mach numbers of approximately 0.1 to 0.2. Jet-to-target plate distances Z of 1.5D, 3.0D, 5.0D, and 8.0D are employed, where D is the impingement hole diameter. Streamwise and spanwise hole spacings are 8D. Local and spatially-averaged Nusselt numbers show strong dependence on the impingement jet Reynolds number for all situations examined. Experimental results also illustrate the dependence of local Nusselt numbers on normalized jet-to-target plate distance, especially for smaller values of this quantity. The observed variations are partially due to accumulating cross-flows produced as the jets advect downstream, as well as the interactions of the vortex structures, which initially form around the jets and then impact and interact as they advect away from stagnation points along the impingement target surface. The highest spatially-averaged Nusselt numbers are present for Z/D = 3.0 for Re_j of 8200, 20,900, and 30,000. When Re_j = 52,000, spatially-averaged Nusselt numbers increase as Z/D decreases, with the highest value present at Z/D = 1.5.