Heat transfer and pressure drop in a square spiral channel roughened by in-line skew ribs

This experimental study examines the detailed Nusselt number (Nu) distributions, pressure drop coefficients (f) and thermal performance factors (TPF) for a square spiral channel with two opposite endwalls roughened by in-line 45° ribs. Detailed Nu distributions over the rib floor with forward and backward flows are measured using the steady-state infrared thermo-graphic method at Reynolds numbers (Re) of 900–30,000. With the increased f from the smooth-walled straight tube references (f∞), the rib-induced sectional vortical flows interact with the centrifugal-force driven Dean vortices along the entire spiral passage to generate the considerable heat transfer enhancement (HTE) impacts that raise the area-averaged turbulent Nusselt numbers (image) to 8.41–3.66 and 5.05–2.78 times of the Dittus–Boelter Nusselt numbers (Nu∞) for forward and backward flows at 2700 ⩽ Re ⩽ 30,000, respectively. Comparisons of image and TPF obtained from the ribbed spiral channel with other types of HTE devices reveal the thermal performances of the present HTE measure. Two sets of image and f correlations for the square spiral ribbed duct with forward and backward flows are generated to assist the design applications using this HTE measure.