NEWTONIAN / NON-NEWTONIAN FORCED AND MIXED CONVECTIVE HEAT TRANSFER AND FLUID FLOW PAST A PAIR OF TANDEM CYLINDERS

Abstract

The current work concerns with the 2-D numerical study of flow and heat transfer of a Newtonian and non-Newtonian power law fluids (0.2≤n≤1.0) in both confined and unconfined channels for tandemly arranged cylinders. Involved equations are solved by finite volume-based method code for different gap ratios (2.5D to 5.5D) with varying Richardson number (0≤Ri≤1, for confined channel) at fixed Re=100 for confined channel and varying Reynolds number from 20≤Re≤40 for unconfined channel. Prandtl number for Newtonian and non-Newtonian fluids are taken as 0.7 (air) and 50 (n-butanol) respectively. Outcomes are presented in terms of different flow and thermal parameters like lift coefficients, drag coefficients, Strouhal number, local and surface average Nusselt number. For confined case we observed a sudden jump in physical parameters, spacing at which this phenomena occurs is termed as critical spacing. In confined channel the introduction of thermal buoyancy (Ri >0) made a deep impact on calculated physical parameters and it is noted that the critical spacing shifts towards a lower value for increasing Richardson number. Analysis of lift coefficients shows that the fluctuations in lift signal shifts from zero average value for Ri =0 towards a non-zero negative average value for both cylinders for Ri >0. In case of non-Newtonian fluid at Ri=0 with decrease in power law index (n) critical spacing keeps on increasing and vice-versa effect can be observed for Ri=1. In unconfined channel with increase in Reynolds number the drag decreases and Nusselt number for both the cylinders keeps on increasing. It was also observed that the percentage increment in the physical parameters of the downstream cylinder for both confined and unconfined channel is much more than its upstream counterpart.