Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs

The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1—q″_r1/q″_s = q″_r2/q″_s = 1; Case 2—q″_r1/q″_s = q″_r2/q″_s = 3; Case 3—q″_r1/q″_s = q″_r2/q″_s = 6; Case 4—q″_r1/q″_s = 6 and q″_r2/q″_s = 4; Case 5—q″_r1/q″_s = q″_r2/q″_s = ∞; Case 6—q″_r1/q″_s = ∞ and q″_r2/q″_s = 0) were studied for four rib orientations (90 deg rib, 60 deg parallel rib, 60 deg crossed rib, and 60 deg V-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5—q″_r1/q″_s = q″_r2/q″_s = ∞) provides a higher ribbed side wall heat transfer augmentation than the four-wall uniform heating (Case 1—q″_r1/q″_s = q″_r2/q″_s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60 deg V-shaped rib and 60 deg parallel rib perform better than the 60 deg crossed rib and 90 deg rib, regardless of wall heat flux ratio and Reynolds number.