Hh. Cho et al., EXPERIMENTAL MASS (HEAT) TRANSFER IN AND NEAR A CIRCULAR HOLE IN A FLAT-PLATE, International journal of heat and mass transfer, 40(10), 1997, pp. 2431-2443
Experiments are performed to investigate the local heat/mass transfer
characteristics for flow through a single circular hole in a thin perf
orated plate (modeling a combustor wall). The naphthalene sublimation
technique is employed to determine the local values on the hole's inne
r surface and in the vicinity of the hole entrance and exit. The hole-
length-to-diameter ratio varies from 0.5 to 1.5, and the ratio of the
diameter of the outer boundary (active area) to the hole diameter vari
es from 1.5 to 4.5. The Reynolds number based on the hole diameter is
between 600 and 30 000. On the windward surface, the heat/mass transfe
r coefficient increases rapidly as the flow approaches the hole entran
ce due to flow acceleration with a thin boundary layer. Inside the hol
e, a separation zone at the hole entrance decreases with increasing Re
ynolds number and then remains constant, approximately 0.56 hole diame
ter in depth, as the Reynolds number is increased further. The mass tr
ansfer coefficient al the reattachment point is about four times that
for fully-developed tube flow. The mass transfer variations indicate a
laminar separation and a turbulent reattachment flow in this Reynolds
number range. The transfer coefficient on the leeward surface is smal
l for the single hole flow because of a weak entrainment-flow velocity
. The overall transfer rate is dominated by the inside hole surface (a
pproximately 60%) in spite of its small surface area. Correlations are
proposed for local/average heal transfer in short single holes as a f
unction of Reynolds numbers and hole aspect ratios. (C) 1997 Elsevier
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