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MIXED CONVECTION IN POWER-LAW FLUIDS FROM TWO CONFINED CYLINDERS IN A SQUARE DUCT: EFFECT OF CROSS BUOYANCY

L. Mishra
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P., India

Rajenda P. Chhabra
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P.208016, India

DOI: 10.1615/IHMTC-2017.2160
pages 1559-1566

Abstract

This work provides some insights into the mixed convection heat transfer from two heated circular cylinders in the cross-flow of power-law fluids confined in a square duct with single inlet and outlet ports. The coupled governing differential equations, namely, continuity, momentum and energy have been numerically solved using the finite-element method to study the momentum and heat transfer characteristics due to the combined effects of the buoyancy-induced convection acting perpendicular to the forced convection. This work also serves as an extension to our previous studies for natural [1, 2] and forced convection [3] heat transfer from two identical or differentially heated circular cylinders in a square duct. The numerical results obtained for the velocity and temperature fields have been analyzed in terms of streamlines, isotherm contours, local and average Nusselt number distribution for the following ranges of the relevant dimensionless parameters: 5 ≤ Re ≤ 200; 1 ≤ Pr ≤ 100, 0.1 ≤ Ri ≤ 5, and 0.2 ≤ n ≤ 2. The variation in the heat transfer with the power-law fluid behavior and thermal buoyancy has been delineated. The Reynolds and/or Prandtl numbers have a positive influence on heat transfer while the cross buoyancy causes asymmetry in the flow and thermal patterns. The introduction of buoyancy also leads to augmentation of heat transfer as indicated by the variation of the values of the local and average Nusselt numbers, especially in shear-thinning fluids. The secondary flows developed coupled with the fluid acceleration due to confinement further influence the rate of heat transfer which exhibits an inverse dependence on the power-law index. Thus, it can be concluded that the cross-buoyancy slightly enhances heat transfer for this configuration, especially in shear-thinning fluids.

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