Effect of Channel Orientation on Heat Transfer in Rotating Smooth Square U-Duct at High Rotation Number

Abstract

The effect of channel orientation on heat transfer in a rotating, two-pass, square channel is experimentally investigated in current work. The classical copper plate technique is employed to measure the regional averaged heat transfer coefficients. The inlet Reynolds number and Rotation number range from 25000 to 35000 and 0 to 0.82, respectively. Five different channel angles (−45°, −22.5°, 0°, 22.5°, 45°) are selected to study the effect of channel orientation on heat transfer. In the radially outward flow channel, the surface average heat transfer in β = 0° channel are higher than those in angled-channel (±22.5°, ±45°) on the trailing surface at all Rotation number ranges (0–0.82). While on the leading surface, surface average heat transfer are lower before a critical Rotation number, and turn higher after the critical point. Channel orientations show less influence on heat transfer in the radially inward flow channel. Compared with their corresponding perpendicular channel orientation values (β = 0° channel), heat transfer in angled-channels decrease on the pressure side and increase on the suction side at a relatively lower Rotation number (Ro<0.4) for both inward and outward channels. While at higher Rotation number (Ro>0.4), heat transfer in angled-channel decrease on both the leading and trailing walls in the first pass, and increase on both the leading and trailing walls in the second pass. By considering the effect of channel orientations, the relation between critical Rotation number on the leading surface in the first pass and dimensionless location (X/D) obeys a simple rule: (Roc·X/D)·cosβ = 1.31. The trailing-to-leading heat transfer differences induced by rotation increase with the increasing of Rotation number in angled-channel, and they are larger than β = 0° channel after the critical Rotation number in both passages.