Heat Transfer in Smooth and Ribbed Rectangular Two-Pass Channels with a Developing Flow Entrance at High Rotation Numbers

摘要

Cooling channels with a developing flow entrance condition and aspect ratios of1:4 and 2:1 were studied. The range of the rotation number and buoyancy parameter forthe selected AR channels was extended. The maximum Ro and Bo for the 1:4 channelwas 0.67 and 1.9, respectively. For the 2:1 channel, these values were 0.45 and 0.85,respectively.The effect of rib spacing and rib height on heat transfer in the 1:4 channel isinvestigated. Three rib spacing configurations were considered: P/e=2.5, 5, 10 with aconstant e/Dh ratio of 0.078. To investigate the effect of rib height, a rib configurationwith an e/Dh ratio of 0.156 and P/e ratio of 10 was considered. For the 2:1 channel, asmooth channel surface condition was studied. For each channel aspect ratio and surfacecondition, five Reynolds numbers were studied up to 40K. At each Re, five rotationalspeeds are considered up to 400 rpm.The results of this research work indicate that rotation can cause a significantincrease in heat transfer on the first pass trailing surface of both aspect ratio channels. The leading surface in ribbed channels has shown a dramatic decrease in heat transferwith rotation in the first pass. Reductions in heat transfer by as much as 50% wereobserved. In the second pass, the leading and trailing surfaces with ribs showed verysimilar effects of rotation. Also, the effect of rotation seems to vary with the rib spacing.The strength of rotation showed to be greater in the tight rib spacing of P/e=2.5. The ribheight in the 1:4 channel had minimal impact due to the large distance between theleading and trailing surfaces. The tip cap heat transfer for both channels showed largeincreases with rotation. This is very beneficial since tip cooling is an important part ofmaintaining the life a turbine blade. Finally, the buoyancy parameter proved to be veryuseful in predicting heat transfer in rotating conditions. The correlations developedshowed very acceptable accuracy when compared to the experimental data.