Heat transfer in rotating spiral channel with two opposite planar walls roughened by skew ribs

Heat transfer performances in a radially rotating spiral channel with two opposite planar endwalls roughened by in-line 45 degrees ribs at speeds of 0-900 rev/min are experimentally examined. Airflow enters this rotating channel from the spiral eye and flows spirally outward with different co- and counter rotating conditions at which the Coriolis secondary flows respectively enrich and suppress the combined vortices tripped by skew-ribs and centrifugal forces. Local Nusselt numbers along the centerlines of the inner/outer smooth curved walls and the ribbed planar endwall are individually measured at Reynolds numbers (Re) of 750-30,000, rotation numbers (Ro) of 0-3.09 and buoyancy numbers (Bu) of 0.00038-7.88 with co- and counter rotations. In the static channel, the rib-induced sectional flows enrich Dean vortices to raise the mean centerline-averaged Nusselt numbers ((Nu) over bar (0,mean)) to 5.79-9.84 and 3.37-2.11 times of the straight plain duct references (Nu(infinity)) at laminar and turbulent conditions, respectively. In the rotating channel, the rotation induced Coriolis and centrifugal forces act synergetically to generate various degrees of heat transfer impacts on the inner, outer and ribbed channel walls. A set of selected heat transfer data illustrates the differential rotational-force effects on local Nu and the averaged Nusselt numbers ((Nu) over bar) along the centerlines of rotating inner, outer and ribbed walls by analyzing the interdependent and isolated Re, Ro and Bu impacts on Nu and (Nu) over bar at co- and counter rotating conditions. Due to the combined Re, Ro and Bu effects, (Nu) over bar/(Nu) over bar (0) ratios over the inner, outer and ribbed walls with co- and counter rotations respectively fall in the ranges of 1.08-3.01,1.03-2.6 and 1.01-2.19 at co-rotating conditions and 1.01-2.63.2.68-1.87 and 0.74-2.13 with counter rotations. A set of physically consistent heat transfer correlations is generated to permit the evaluation of individual and interdependent Re, Ro and Bu impacts on Nu over each constituent channel wall for this rotating spiral ribbed channel. (C) 2012 Elsevier Masson SAS. All rights reserved.