Turbulent flow of air with variable properties in a set of regular polygonal ducts and circular tube have been numerically simulated. All the ducts have the same hydraulic diameter as their characteristic length dimension in the Reynolds number. The flow is modeled as three-dimensional and fully elliptic by using the finite volume method and the standard k-ε turbulence model is adopted. The performances of the flow and heat transfer have been thoroughly investigated. The results showed that comparatively strong secondary flow can be observed with variable properties fluid. For the regular polygonal duct, the local heat transfer coefficient along circumferential direction is not uniform and there is an appreciable reduction in the corner region. The use of hydraulic diameter for regular polygonal ducts to determine turbulent flow heat transfer from circular tube correlations leads to unacceptably large errors. Based on the simulation results, a correction factor Cϕ is proposed to ameliorate the previous correlations, and the error in the prediction of turbulent heat transfer with the new correlation is within 6%.

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