Entropy generation for two-dimensional convective flows in square enclosures

Numerical simulation studies of buoyancy-driven natural convection and lid-driven mixed convection are performed in a two-dimensional square enclosure. The Bhatnagar-Gross-Krook collision model-based lattice Boltzmann method with a double distribution function is employed. The effect of various non-dimensional numbers on total entropy generation (Stotal), average Nusselt number (Nu) on the hot wall, and Bejan number (Be) is studied. The Stotal in a differentially heated square cavity, case A is a linear function of Rayleigh number (Ra) and irreversibility ratio, and it reduces as the Prandtl number (Pr) decreases for a given Ra. The Be reaches a minimum value at the maximum Stotal. The significant contribution of fluid friction irreversibilities is observed in the entropy generation for stable one-sided lid-driven dominated flows (Richardson number, Ri & DLANGBRAC; 1), case B, wherein the prominent shear effect is observed close to the moving lid. In contrast, buoyancy-dominated flows (Ri & drangbrac; 1) induce greater entropy generation due to the intensity of velocity variations and thermal gradients at the domain boundaries in the case of unstable two-sided lid-driven flows, case C. Thus, enhancing the steady state behavior of Nu and Stotal with Grashof number (Gr). Case B decelerates both quantities with an increase in Gr. The entropy criterion between Nu and Stotal is maximum at Gr = 106, and it varies based on the thermal conditions and Pr. The flow's kinetic energy is higher for Ri & DLANGBRAC; 1 and decreases with an increase in Gr for case B, while case C enhances kinetic energy for significant velocity variations at the boundaries.

Automated summary

Numerical simulation studies were conducted on buoyancy-driven natural convection and lid-driven mixed convection in a two-dimensional square enclosure using the Bhatnagar-Gross-Krook collision model-based lattice Boltzmann method. The effect of various non-dimensional numbers on total entropy generation, average Nusselt number on the hot wall, and Bejan number was investigated. It was found that the total entropy generation is linearly dependent on the Rayleigh number and irreversibility ratio, and decreases with decreasing Prandtl number. The Bejan number reaches a minimum value at the maximum total entropy generation. The study also revealed the significant contribution of fluid friction irreversibilities and the influence of buoyancy and velocity variations on entropy generation in different flow regimes.