Optimization of L‐ and C‐Shaped Enclosures for Natural Convection Flow: Thermal Performance and Irreversibility Analysis by Using Finite Element Method in FEniCS

This study provides a comprehensive finite element analysis of natural convection and entropy generation in L‐shaped and C‐shaped enclosures. The analysis considers a Prandtl number () of , a Grashof number range of , and a Rayleigh number range of . The simulations are conducted using the open‐source computational platform FEniCS. The investigation focuses on optimizing geometric parameters to enhance thermal performance while minimizing irreversibility. For L‐shaped enclosures, extending the horizontal arm initially intensifies buoyancy‐driven circulation and improves heat transfer, but leads to increased entropy production due to viscous dissipation. Beyond a critical length (), the benefits diminish and irreversibility decreases due to smoother thermal and flow fields. In contrast, increasing the vertical arm length () improves thermodynamic efficiency by broadening the plume path and promoting uniform mixing, without significantly affecting heat transfer rates. For C‐shaped enclosures, optimal thermal performance with moderate entropy generation is observed at narrow and shallow recesses (), which sustain a strong, singular circulation cell. As the recess deepens or widens (), multiple vortices form, leading to increased irreversibility despite fair heat transfer. Excessive recess dimensions degrade flow and sharply raise entropy generation. Across all configurations, increasing the Rayleigh number () enhances convective heat transfer but also escalates thermal irreversibility, which remains the dominant source of entropy generation over viscous effects. Optimal performance is achieved in L‐shaped enclosures with and in C‐shaped cavities with minimal cutout size, offering a balanced strategy for maximizing natural convection efficiency with reduced thermodynamic losses.