Perturbation of the heat transfer and the friction factor of a rib roughened surface in an annular passage due to localised removal of the ribbing

The paper describes part of experimental work concerned with the measurement of the flow losses due to, and the convective heat transfer from, the ribbed core of a rough-smooth annulus, where the ribbing has been partially or totally removed from relatively small locations. Air was forced through the annular passage formed by a helically ribbed fuel cladding can placed within a smooth circular tube. The fuel can was heated by passing a large direct current through it. The temperature of the bore of the ribbed can, at the location of the disrupted ribbed surface, was measured by sliding in a probe supporting eight springloaded thermocouple junctions. The temperature values were recorded at a number of flow rates and electrical power settings. The measurements show that the local impairment may, in some instances, be worse than that expected from correlations of heat transfer which apply to uniformly reduced ribbing. On the other hand, at low flows, where the ribs cease to have a large effect on the flow, the heat transfer due to the reduced ribbing was better than might have been expected. © 1999 Elsevier Science S.A. All rights reserved.