An experimental study of heat transfer in the turn region of a U-bend channel with various ribs

The detailed heat transfer distributions and pressure drop in the turn region of a U-bend channel with and without ribs have been experimentally investigated using liquid crystal thermography. The Reynolds numbers based on hydraulic diameter of the channel and the bulk velocity are 20,000 and 26,000. The ribs are mounted on the outer wall surface in the turn region of the U-bend channel; the rib height-to-hydraulic diameter ratio is 6%; the rib pitch-to-height ratio is 12; and the rib configurations studied are transverse (90°), angled (45°, 60°), and V-shaped (45°, 60°) with tip facing downstream and upstream. Results indicate that heat transfer on the smooth outer wall is dominated by the flow impingement. In the presence of ribs, the heat transfer patterns are significantly altered due to the combined effects of the sharp turn and ribs. Based on the average heat transfer and pressure drop, thermal performance is evaluated and heat transfer non-uniformity is also considered to provide better rib configurations