Forced Convection Heat Transfer in Power Law Liquids from a Pair of Cylinders in Tandem Arrangement

Forced convection heat transfer characteristics for the flow of incompressible power law fluids over a pair of cylinders (of equal diameters) in tandem arrangement has been studied in the two-dimensional, steady cross-flow regime. The field equations have been solved using a finite volume method based solver (FLUENT 6.2) over the ranges of conditions as follows: power law index (0.2 <= n <= 1.8), Reynolds number (1 <= Re <= 40), Prandtl number (1 <= Pr <= 100), and the gap ratio between the two cylinders (2 <= G <= 10). Extensive results on the isotherm patterns, centerline temperature profiles, and local and average Nusselt numbers have been presented in detail, for the two commonly used thermal boundary conditions, namely, constant temperature or constant heat flux prescribed on the surface of the two cylinders. While the upstream cylinder shows characteristics similar to an isolated cylinder, the downstream cylinder displays a complex dependence on the relevant dimensionless parameters. As expected, at large values of the gap ratio (G), the behavior of the downstream cylinder approaches that of a single cylinder, thereby suggesting no or weak interference between the two cylinders. Depending upon the values of G and n, both the wake interference and power-law rheology influence the heat transfer characteristics to varying extents. Generally, the upstream cylinder shows higher values of the average Nusselt number than the downstream cylinder. On the other hand, the average Nusselt number for both cylinders is seen to be smaller than that for a single cylinder under otherwise identical conditions. With reference to Newtonian fluids, the shear-thinning behavior promotes heat transfer, whereas shear-thickening lowers it. Finally, simple predictive correlations are developed to estimate the value of the average Nusselt number or the j-factor in a new application.