Buoyancy and blockage effects on transient laminar opposing mixed convection heat transfer from two horizontal confined isothermal cylinder in tandem*

Transient mixed convection in a laminar cross-flow from two isothermal cylinders in tandem arrangement confined inside a vertical channel is studied numerically using the vorticity-stream function formulation of the unsteady two-dimensional Navier-Stokes and energy equations. Numerical experiments are performed for a Reynolds number based on cylinder diameter of Re $=$ 200, Prandtl number of Pr $=$ 7, blockage ratio of D/H $=$ 0.2, a pitch-to-diameter ratio of L/D $=$ 2, and several values of buoyancy strength or Richardson number Ri $=$ Gr/Re$^{\mathrm{2}}$. The results reported herein demonstrate how the wall confinement, interference effects and opposing buoyancy affect the flow structure and heat transfer characteristics of the cylinder array.