Endwall heat transfer and pressure drop in rectangular channels with attached and detached circular pin-fin array

Endwall heat transfer and pressure drop characteristics in four rectangular channels with a channel aspect ratio of 4 and the staggered arrays of circular pin-fins with four clearances (C) between pin-tips and the measured endwall of 0, 1/4, 1/2 and 3/4 pin-diameter (d) are examined comparatively at Reynolds numbers (Re) of 10,000, 15,000, 20,000, 25,000 and 30,000 to determine the effects of pin-tip leakages on the endwall heat transfer and on channel inlet-to-exit pressure drops. The accelerated flows through pin-to-endwall clearances modify the protrusion-endwall interactions that affect the horseshoe vortices as well as the downstream wakes and shear layer separations. By way of increasing C/d ratio from 0 to 3/4, the area averaged endwall Nusselt numbers decrease with substantial reductions in channel inlet-to-exit pressure drops. The endwall heat transfer level with detached pin-fins at C/d = 1/4 is somewhat less than that with attached pin-fins but the pressure drop coefficient of the former is much lower than that of the later, which leads to the highest thermal performance factor among the four comparative cases in the Re range examined by this study. A set of correlations that evaluate the area averaged endwall Nusselt number and the pressure drop coefficient with Re and C/d as the controlling parameters are derived.