Variable Property Nusselt Numbers in a Channel with Pin Fins

摘要

Nusselt numbers and friction factors are presented that show the effects of temperature ratio and variable properties in a rectangular channel with pin fins and an aspect ratio of 8. The ratio of air inlet stagnation temperature to local surface temperature T_(0i)/T_w varies from 0.68 to 0.93, and Reynolds numbers based on channel height range from 1.8 x 10~4 to 3.38 x 10~4. The pins are placed in 12 rows, with pin diameter and spacing between adjacent pins in both directions all equal to the channel height. Ratios of globally averaged Nusselt numbers to baseline, constant-property Nusselt numbers, Nu/Nu_(0,cp), increase by about 35% as the temperature ratio T_(0i)/T_w decreases, provided that Reynolds number Re_H is approximately constant and that the base areas beneath the pins are not considered. When heat transfer from the pin fins is also included, this increase is about the same. Friction factor ratios f/f_(0,cp) decrease as T_(0i)/T_w decreases over this same range of values. Such global Nusselt number changes are a result of local Nusselt number ratio increases with decreasing temperature ratio, which are especially pronounced beneath the wake and shear layers that are present downstream of each pin and beneath the horseshoe vortex that forms just upstream of each pin tin.