Three-dimensional natural convection in an enclosure with four cylinders: Effects of vertical spacing on flow and heat transfer

This study numerically investigated three-dimensional natural convection of an incompressible fluid in an enclosure containing four heated cylinders, focusing on the effects of vertical spacing on flow and heat transfer. Unsteady simulations were conducted using an in-house Fortran-based finite volume solver. The vertical spacing between the cylinders ranged from 0.1 ≤ ε v ≤ 0.5, and the Rayleigh number varied from 10 4 to 10 6 . As the Rayleigh number increased, heat transfer shifted from conduction-dominated to convection-dominated, with more complex and unstable flow patterns. Vertical spacing significantly affected flow stability, heat transfer performance, and temperature distribution. At ε v =0.2, the flow showed quasi-periodic behavior, while larger spacings led to more irregular and unsteady flows, reducing three-dimensional effects. Heat transfer increased with spacing for all Rayleigh numbers. Notably, at ε v =0.1 at Ra =10 6 , three-dimensional simulations showed distinct differences from two-dimensional results, indicating the importance of three-dimensional effects. Finally, an artificial neural network (ANN) was also used to predict heat transfer performance.