Impact of mixed convection on flow dynamics and heat transfer through an isotropic porous triangular array of periodic heated/cooled cylinders

The effect of aiding and opposing buoyancy (-1 <= Ri <= 1) on flow and heat transfer across cylinders specifically arranged in an equilateral triangular array in a heat exchanger has not previously been studied. Periodic boundary condition in the transverse direction is imposed where porosity of the array ranges from 0.7 to 0.99. The influence of buoyancy and Prandtl number (1 and 50) on the flow structure and its effect on the overall heat transfer is thoroughly elucidated in the present work. The impact of aiding/opposing buoyancy on the thermal performance of the array is predominant at higher porosities. The average drag of the array of cylinders increases with an increase in the aiding buoyancy and decreases with an increase in opposing buoyancy with respect to forced convection. The porosity of the triangular array has an inverse relation with the average drag coefficient, barring few exceptions which are explained in detail in the present work. The heat exchange is assertively higher at opposing-buoyancy cases for all values of porosity and Prandtl number. The present results are in agreement with the available experimental/numerical studies.