Effect of boundary conditions on heat transfer and entropy generation during two-phase mixed convection hybrid Al2O3-Cu/water nanofluid flow in a cavity

In this work, the effect of three different boundary conditions on the fluid flow and heat transfer is analyzed for mixed convection in a differentially heated double sided lid-driven square cavity. The current work deals with water-based hybrid Al2O3-Cu/water nanofluid with volume fractions phi <= 3%. We use thermal lattice Boltzmann (LB) method to simulate two-phase nanofluid flow for discretely varying Richardson number (0.1 <= Ri <= 10) at fixed Grashof number of Gr = 10(4). The experimental and numerical validations of current two-phase LB model show better accuracy in predicting nanofluid behaviour compared to single-phase LB model. Examination of the second law of thermodynamics-based energy efficiency reveals that the heat transfer rate and total entropy generation of the current system are influenced by the change in boundary condition and Richardson number. The addition of nanoparticles is unable to attain desirable effectiveness in the overall improvement of the current thermal system due to augmentation of entropy generation, despite the improvement of heat transfer rate. The current results suggest two different optimal volume fractions based on the maximum heat transfer rate and performance coefficient parameter respectively.