Rib-Spacing Effect on Heat Transfer in Rectangular Channels at High Rotation Numbers

This study experimentally determined the effects of rib spacing on heat transfer in a rotating 1:4 AR channel with a sharp-bend entrance. The leading and trailing walls used 45 deg angled ribs. The rib-height-to-hydraulic-diam ratio e/D-h, was 0.078. The rib-pitch-to-rib-height ratios P/e studied were P/e = 2.5,5, and 10. Each ratio was tested at five Reynolds numbers up to 40,000. For each Reynolds number, experiments were conducted at five rotational speeds up to 400 rpm. Results showed that the sharp-bend entrance has a significant effect on the first-pass heat transfer enhancement. In the second pass, the rib spacing and rotation effect are reduced. The P/e = 10 case had the highest heat transfer enhancement, based on the total area, and the P/e = 2.5 had the highest heat transfer enhancement, based on the projected area. The current study has extended the range of the rotation number Ro and local buoyancy parameter Bo(x) for a ribbed 1:4 AR channel up to 0.65 and 1.5, respectively. Correlations for predicting heat transfer enhancement due to rotation in the ribbed 1:4 AR channel, based on the extended range of the rotation number and buoyancy parameter, are presented in the paper.