Flow and heat transfer of impinging jet array associated with entrained air ducts

Abstract

The purpose of this research was to investigate experimentally and numerically the effects of an impinging jet array with entrained air ducts on heat transfer. Straight pipes with 17.2 mm inner diameter (d) and 300 mm length (l) were in a 5 × 5 nozzle array with in-line configuration. The length of air duct (L) was varied among L/d = 2, 4, or 6, and the diameter of the duct (D) satisfied D/d = 2, 4, or 6. The jet-to-surface distance (H) was tested at H/d = 4, 6, or 8; and the jet-to-jet spacing (S) was among S/d = 4, 6, or 8. Reynolds number (Re) in the jets was from 10,000 to 40,000. Conventional impinging jets were also examined for benchmarking. Flow characteristics obtained numerically from v2f turbulence model were also presented to explain the heat transfer mechanisms. The results indicated that heat transfer rates on the target surface became higher when the duct was elongated, and was more widely spread when the duct diameter was expanded. These effects were more marked in cases with narrow jet-to-jet spacing (S/d = 4) and with large jet-to-surface distance (H/d = 8). Moreover, a heat transfer correlation was constructed from the experimental results to predict heat transfer rates within the studied ranges of parameters.