Entropy generation and natural convection in rectangular cavities

This work presents a numerical analysis of entropy generation in rectangular cavities that were submitted to the natural convection process. This natural convection process was caused by temperature differences between the vertical walls of the cavities. Momentum and energy equations were used to solve this problem. These equations were coupled by the Boussinesq approximation. Initially the cavities were submitted to uniform temperature and velocity fields. The hypothesis of perfect insulation was considered for the top and bottom walls of the cavity. Impermeability and non-slip condition in the boundary were assumed for every wall of the cavity. The numerical analysis is performed through a two-dimensional model with the Finite Volume method. The results of the entropy generation obtained to a square cavity were used to validate the numerical model and it presented good concordance with results from other authors. Additionally, an analysis of the entropy generation in rectangular cavities was performed with five aspect ratios, five Rayleigh numbers and four irreversibility coefficients. The results of this work indicate that: (a) the total entropy generation in steady state increases linearly in both cases, the aspect ratio and the irreversibility coefficient, and exponentially with the Rayleigh number; (b) the influence of the aspect ratio on Bejan number is proportional to Rayleigh number and inversely proportional to the irreversibility coefficient; (c) for the same aspect ratio, the entropy generation due to the viscous effects increases with the Rayleigh number and, for a certain Rayleigh number, the entropy generation due to the viscous effects also increases with the aspect ratio.