Heat Transfer in Square Channels with Wedge-Shaped and Delta-Shaped Turbulence Promoters

The effect of rib configuration on local heat transfer coefficients and pressure drop in a square channel with two opposite in-line ribbed walls was investigated at Reynolds numbers from 15,000 to 80,000. Two types of rib configurations were studied. The first group is a wedge-shaped rib with the rib height-to-hydraulic diameter ratio of 0.125 and the rib pitch-to-height ratio of 5 or 10. Both full length and broken ribs are studied. The second group is a delta-shaped rib with the rib height-to-hydraulic diameter ratio of 0.125 and the rib pitch-to-height ratio of 5. Both aligned and offset arrangements are studied for a forward and backward direction relative to the mainstream flow. Results show that, for the delta-shaped rib, the backward flow direction has higher heat transfer than the forward flow direction, and the aligned arrangement is better than the offset arrangement. The broken configuration for the wedge-shaped rib performs better than the full length one. In general, the delta-shaped rib performs better than the wedge-shaped rib. The backward delta-shaped aligned rib configuration produces the highest heat transfer augmentation (3-4 times), while the backward delta-shaped offset rib creates the smallest pressure drop penalty (5-6 times). Results also show that the surface heat flux ratio has significant effect on the smooth-side heat transfer augmentation, while the effect on the ribbed-side is relatively small.