Experimental investigation of laminar mixed convection in an inclined semicircular duct under buoyancy assisted and opposed conditions

Combined free and forced convection is experimentally investigated for lami nar water flow in the entrance region of a semicircular duct with upward an d downward inclinations within +/-20 degrees using the boundary condition o f uniform heat input axially. The experiment was designed for determining t he effect of inclination (particularly the downward) on the wall temperatur e, and the local and fully-developed Nusselt numbers at three Reynolds numb ers (500, 1000, and 1500) and a wide range of Grashof numbers. For the upwa rd inclinations, Nusselt number was found to increase with Grashof number a nd the inclination angle (up to 20 degrees), while the effect of Reynolds n umber was found to be small. For the downward inclination, Reynolds number has a strong effect on Nusselt number and the manner by which it varies wit h Grashof number. The fully-developed values of Nusselt number agree well i n magnitude and trend with theoretical results recently obtained by the aut hors. (C) 2000 Elsevier Science Ltd. All rights reserved.