Exploring thermodynamic processes through CFD of free convection of Bingham fluids in innovative hexagonal enclosure (Papanastasiou model)

This research presents a unique enclosure geometry, namely, a hexagonal finned cavity, for the analysis of Bingham–Papanastasiou fluid natural convection, which is examined numerically through COMSOL Multiphysics. The momentum and energy equations that govern the phenomena are solved via the Galerkin approach. The external walls have been assumed to be cold, while the inner wall has been taken as hot. A thorough investigation of the thermo-hydrodynamic flow is carried out considering the nominal value of the Rayleigh number (Ra), the range of plasticity Bn (1–50), and the obstacle lengths L (0.1, 0.4). The findings demonstrate that the rate of heat transfer ( Nu ) is positively correlated with the buoyancy parameter (Ra) while it is inversely related to the plasticity parameter (Bn), with larger values of the latter resulting in lesser heat transfer. This reduction seems to occur due to lame yield stress at a bigger Bn, damping the fluid flow inside the enclosure. The streamline patterns further confirm this trend, showing a significant weakening of circulation at high plasticity levels, particularly for Bn = 50. The effect of obstacle length can be seen on the streamline and isotherm contours, which may indicate the intermediate fin length (L = 0.2) for Rayleigh Number (Ra) as the best, as it increases vortex creation and supports good circulation in the cavity, thus enhancing the heat transfer performance.