Effects of Flow Gap Atop Pin Elements on the Heat Transfer From Pin Fin Arrays

Abstract

This study investigates the effect of gap atop an inline array of cubic fins on the heat transfer from various participating surfaces in the channel housing the array. Five different gap sizes of C/H = 0.25, 0.5, 1.0 and 2.0, as well as the baseline case without gap (C/H = 0.0) are examined and compared. The array consists of twelve rows of three columns. All tests use a unified Reynolds number at 16,000 based on the mean velocity in the channel and cube height. The heat transfer measurement uses a liquid crystal imaging technique combined with a one-dimensional, transient conduction mode) and a lumped heat-capacity model. The results reveal that the heat transfer from the surfaces uncovered by the cubic fins in the test channel generally decreases with the size of the clearance atop the array. However, such a decreasing trend is insignificant for cases with relatively smaller gaps, i.e. C/H = 0.25 and 0.5. Under these conditions, the heat transfer from the surface of cubic fin, in fact, is higher than that of the baseline case. The vortex enriched shear layer separated from the sharp edges around the cube top is considered to be responsible for this phenomenon.