Local heat transfer in a rotating smooth and ribbed U-shaped channels

Experiments are made to determine the local heat transfer performances in a U-shaped square channel with smooth walls and those with ribbed surfaces. The rib turbulators are placed symmetrically on the trailing and leading walls with an angle of attack of 90°. The rib height-to-hydraulic diameter (e/D_h) is 0.143; the rib pitch-to-height ratio (P/e) is 7. The Reynolds number and rotation number are varied in 6100-25100, and 0-0.26, respectively. Results for the smooth serpentine channel are compared with those for rib-roughened one. These results show that a significant enhancement in the heat transfer is achieved by means of rib turbulators in a serpentine channel in stationary state as well as in rotation state. The heat transfer of the first pass trailing surface and the second pass leading surface is enhanced by rotation, whereas the first pass leading surface and the second pass trailing surface show a decrease in heat transfer with rotation. The rotation effect on heat transfer is most significant in the first straight section of the rib roughened channel. The bend induced vortices exert more influence on local heat transfer after 180° sharp turn in the smooth channel.