Flat plate convection heat transfer enhancement via a square rib

Abstract

Flow and convection heat transfer downstream of a square rib on a flat plate were experimentally investigated inside a closed loop wind tunnel. Heat transfer augmentation for the ribbed plate compared to the smooth plate (Nu/Nu0) was studied at Reynolds numbers, based on the rib’s height (H=1cm), of ReH=1.3×103, 2.6×103, 5×103 and 6.3×103. The ribbed plate presented an enhancement in heat transfer (Nu/Nu0>1) at all studied Reynolds numbers. A trend of decreasing enhancement with increasing ReH was observed, with the largest decrease in Nu/Nu0 occurring when ReH increased from 1.3×103 to 2.6×103. The remarkable enhancement in Nu at the lowest Reynolds number (ReH=1.3×103), compared to higher ReH, was presumably due to the transition of the boundary layer regime from laminar to turbulent. To investigate the effect of the rib on the flow over the surface, flow and turbulence structures were measured using an X-probe hot-wire anemometer. It appears that the turbulence generated by the rib (urms, vrms, uv‾) is the most influential factor on enhancing the heat transfer from the surface. Also, the normal velocity (V) created downstream of the rib seems to be somewhat effective in extracting heat from the surface, while the streamwise velocity (U) was blocked by the rib. The energy spectra of normal velocity fluctuations showed traces of vortex shedding from the rib’s edge at ReH=1.3×103.