Numerical Simulation of Turbulent Flow and Heat Transfer in an Anti- Gravity Blind Duct with Tangential Entry Jet

ABSTRACT

This numerical study investigates the flow and heat transfer characteristics in a vertical square blind duct with the coolant fed by a tangential entry jet. The detailed Nusselt number (Nu) distributions over the five constituent walls of the blind duct are calculated at duct (jet) Reynolds numbers Re(Rej) of 5000(20000), 7000(28000) and 10000(40000) using the commercial CFD Star CD code. As an attempt to explore the buoyancy effect on heat transfer performances, three different heat fluxes, which vary the gravitational Grashof numbers (Grg) at the fixed Re, are imposed on each duct wall to vary the buoyancy levels. The jet-induced flow phenomena in the blind duct exhibit various heat transfer impacts on the five duct walls over which the different near-wall flow structures are generated. This is demonstrated by cross-examining the detailed Nu distributions and the area-averaged Nusselt number ( Nu ) over the five duct walls at the tested Re and Grg. The cross-plane swirls induced by the tangential entry jet together with the impinging jet flows considerably elevate the Heat Transfer Enhancement (HTE) performances in the blind duct. Within the parametric conditions simulated, the ratios of Nu to the Dittus-Boelter levels (Nu∞) over the jet wall, back wall, impingement wall, side wall and end wall are respectively raised to 3-5.7, 2.8-5.6, 3-5.8, 2.7-4.8 and 3.1-6.1; while the HTE ratios ( Nu /Nu∞) over these duct walls consistently decrease as Re increases.