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

Abstract

Cooling channels with a developing flow entrance condition and aspect ratios of 1:4 and 2:1 were studied. The range of the rotation number and buoyancy parameter for the selected AR channels was extended. The maximum Ro and Bo for the 1:4 channel was 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 is investigated. Three rib spacing configurations were considered: P/e=2.5, 5, 10 with a constant e/Dh ratio of 0.078. To investigate the effect of rib height, a rib configuration with an e/Dh ratio of 0.156 and P/e ratio of 10 was considered. For the 2:1 channel, a smooth channel surface condition was studied. For each channel aspect ratio and surface condition, five Reynolds numbers were studied up to 40K. At each Re, five rotational speeds are considered up to 400 rpm. The results of this research work indicate that rotation can cause a significant increase 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 transfer with rotation in the first pass. Reductions in heat transfer by as much as 50% were observed. In the second pass, the leading and trailing surfaces with ribs showed very similar 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 rib height in the 1:4 channel had minimal impact due to the large distance between the leading and trailing surfaces. The tip cap heat transfer for both channels showed large increases with rotation. This is very beneficial since tip cooling is an important part of maintaining the life a turbine blade. Finally, the buoyancy parameter proved to be very useful in predicting heat transfer in rotating conditions. The correlations developed showed very acceptable accuracy when compared to the experimental data.