LOCAL FLOW CHARACTERISTICS AND ITS EFFECT ON COWLED FINNED SYSTEMS

An experimental study of local flow characteristics within cowled finn ed systems has been carried out using laser Doppler anemometry (LDA). Such systems are used to control axial temperature profiles within the barrel of an extrusion process. During the experiments, a perspex mod el was used to simulate the actual system, The inlet Reynolds number w ithin the air cowl was 1.72 x 10(4). The local flow between fins was c haracterized by the flow in the curved duct formed by the fin base tub e, fin surfaces and air cowl around the outer diameter of the fins. Th e flow pattern between the fins was measured at the sight windows on t he air cowl wall. The local flow characteristics and its effect on hea t transfer behaviour on tin surfaces were discussed. It was highlighte d that the heat transfer through fin surfaces can be greatly influence d by the local flow characteristics. The mean heat transfer coefficien t in the curved duct was estimated using both empirical equations and experimental results. The mean coefficient was also predicted using a computational fluid dynamics (CFD) package, and was underestimated by 12 per cent when compared with that found using the empirical relation ships.