Mixed convection of shear-thinning nanofluids past unconfined elliptical cylinders in vertical upward flow

The numerical results on mixed convective heat transfer phenomenon between unconfined elliptical cylinders and shear-thinning nanofluids are presented herein. The cylinders are placed horizontally over which nanofluids flowing vertically upward. The governing continuity, momentum and energy equations are simultaneously solved within the limitations of Boussinesq approximation using a commercial computational fluid dynamics based solver. Further the elliptical cylinders and the computational outer domain are considered in full domain so that to effectively delineate the deviation from flow symmetry because of mixed convection. The range of Richardson number in this work is varied widely so that both the forced and natural convections via mixed convection conditions are covered. Before obtaining new results, the conventional numerical procedures of obtaining optimum domain and grid sizes along with appropriate comparisons are followed. The ranges of the pertinent parameters considered herein are as follows: volume fraction of nanoparticles, ϕ = 0.005-0.045; Reynolds number, Re = 1-40; Richardson number, Ri = 0-40; and aspect ratio of elliptical cylinders, e = 0.25-2.5. Finally, the effects of these parameters on the streamlines, isotherm contours, surface pressure, surface vorticity, drag coefficients and local and average Nusselt numbers are thoroughly discussed. Briefly, the total drag coefficient (Cd) decreases with the increasing Re, decreasing Ri and decreasing e. For ϕ ≤ 0.025, Cd decreases with increasing ϕ; however, for ϕ > 0.025 and Re > 20, a reverse trend is seen regardless of values of Ri and e. The average Nusselt number (Nuavg) displayed mixed trends with respect to changes in Ri and e; however, it increases with increasing ϕ and Re regardless of the values of the Richardson number and the aspect ratio of elliptic cylinders.