The flow and heat transfer characteristics of the mixed convection in a horizontal square duct, whose side walls and bottom wall are heated in uniform temperature and upper wall is insulated thermally, are examined numerically in three-dimensional system and transient process. The SIMPLE algorithm and QUICK scheme are applied to solve the governing equations through a control volume. The working fluid is water, and the temperature dependence of kinetic viscosity
ν and thermal conductivity
λ of water is considered in this analysis. Numerical results show that the reverse flow, the spiral flow and two-recirculating flows appear on the upper wall, along the flow direction and near the bottom wall, respectively. The local Nusselt numbers are presented corresponding to the transient flow behavior.
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