Impact of gap-ratios on buoyancy-assisted mixed convection flow and heat transfer in unconfined framework with two side-by-side cylinders

An analysis has been carried out to understand the consequences of side-by-side gap-ratio on thermal buoyancy-assisted two-dimensional flow past a pair of heated circular cylinders for a dominant viscous flow field. This is implemented through studies at Reynolds number (Re) ranging from 5 to 40, Prandtl number (Pr) 0.7, gap-ratio (T/D) 1.5 to 4 and Richardson number (Ri) 0 to 1. An ANSYS-based incompressible flow solver is used with Boussinesq approximation to account for density variations in the momentum equation. One can realize features like the steady-separated and steady-unseparated flow on varying flow and thermal parameters. Unlike streamlines, non-interacting isotherms are non-existent in the current numerical framework. The influence of gap-ratio on enhancement in Nusselt number (Nu) is the best realized at T/D = 1.5 and buoyancy-aided effects play a dominant role for enhancement in Nu at diffusion and/or viscous-dominant conditions occurring at Re = 5. Correlations are developed to quantify the impact of T/D, Re, and Richardson number Ri on Nu. For the first time, Nu's correlation based on varying side-by-side gap-ratio has been stated in a single expression. Finally, a comparison for the heat transfer enhancement/reduction in Nu under a similar numerical framework is provided with cases of high-Pr flow and/or different relatable flow arrangements for circular and square cylinders.