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 measuremen t of the flow losses due to, and the convective heat transfer from, the rib bed core of a rough-smooth annulus, where the ribbing has been partially or totally removed from relatively small locations. Air was forced through th e annular passage formed by a helically ribbed fuel cladding can placed wit hin a smooth circular tube. The fuel can was heated by passing a large dire ct current through it. The temperature of the bore of the ribbed can, at th e location of the disrupted ribbed surface, was measured by sliding in a pr obe supporting eight springloaded thermocouple junctions. The temperature v alues were recorded at a number of flow rates and electrical power settings . The measurements show that the local impairment may, in some instances, b e worse than that expected from correlations of heat transfer which apply t o uniformly reduced ribbing. On the other hand, at low flows, where the rib s cease to have a large effect on the flow, the heat transfer due to the re duced ribbing was better than might have been expected. (C) 1999 Elsevier S cience S.A. All rights reserved.