Heat transfer investigation in rotating smooth square U-duct with different wall-temperature ratios and channel orientations

The correlations between the critical Ro (Roc) and the location (X/D), including wall-temperature ratios (TR) and channel orientations (β), are developed into simple expression. The correlations demonstrate that the minimum heat transfer in the whole channel can be determined by the specified rotational states. And thus the correlations for minimum Nu/Nus ratio as a function of Ro (0 < Ro < 1.0) are developed for different wall-temperature ratios and channel orientations.