JET ARRAY IMPINGEMENT COOLING LOCAL NUSSELT NUMBER VARIATIONS: EFFECTS OF HOLE ARRAY SPACING, JET-TO-TARGET PLATE DISTANCE, AND REYNOLDS NUMBER

Discussed in the article are the combined and separate effects of hole array spacing, jet-to-target plate distance, and Reynolds number on the local surface heat transfer rate for an impinging jet array. The array of impinging jets is directed to one flat surface of a channel which is bounded on three sides. Considered are the Reynolds numbers ranging from 8000 to 50,000, jet-to-target plate distances of 1.5D, 3.0D, 5.0D, and 8.0D, and the streamwise and spanwise hole spacing of 5D, 8D, and 12D, where D is the impingement hole diameter. Also included is a conduction analysis of the impingement cooling array target surface. In general, the local Nusselt numbers generally increase at each x/D location as either the Reynolds number increases, or as the X/D = Y/D hole spacing decreases. The highest Nusselt numbers are generally present at Z/D = 3.0 for Rej values of 8200, 20,000, and 30,000. When Rej = 52,000, the highest measured Nusselt number values are generally present for Z/D of either 1.5, 3.0, or 5.0, depending on the magnitudes of Rej, X/D, Y/D, and streamwise location x/D. The cumulative accumulations of crossflows, from sequential rows of jets, result in sequentially decreasing periodic Nusselt number variations with streamwise development. When examined at a particular value of Rej, the streamwise locations of the local maximum Nusselt numbers also shift to larger x/D locations as Z/D, the normalized jet-to-target distance, increases. The overall result is a complex dependence of local Nusselt numbers on the hole array spacing, jet-to-target plate distance, and impingement jet Reynolds number.