Regularized lattice Boltzmann simulation of double-diffusive convection of power-law nanofluids in rectangular enclosures

Abstract

In this paper, double-diffusive convection of power-law nanofluids in rectangular enclosures is investigated in detail with regularized lattice Boltzmann method. In order to appropriately treat the external force appears in the fluid field, a unified forcing term is also incorporated in the evolution equation such that the Navier–Stokes equations can be recovered correctly. The fluid in the cavity is a water-based nanofluid containing Cu nanoparticles, and the numerical simulations presented here span a wide range of thermal Rayleigh number (104⩽Ra⩽106), volume fraction of nanoparticles (0⩽ϕ⩽0.1), power-law index (0.5⩽n⩽1.5), buoyancy ratio (-1.0⩽Nc⩽1.0), Lewis number (1⩽Le⩽50) and aspect ratio (0.125⩽AR⩽8) to identify the different flow patterns, temperature and concentration distributions. The results show that the augmentation of the nanoparticle volume fraction increases the average Nusselt number but reduces the average Sherwood number. In addition, the average Nusselt and Sherwood numbers are generally decrease with an increase in the power-law index. Further, it was observed that the average Nusselt and Sherwood numbers increase with increasing AR up to an aspect ratio value of ARmax at which the maximum values of Nuav and Shav are obtained. For AR>ARmax, the mean Nusselt and Sherwood numbers start to decrease with increasing AR. What’s more, we also found that the average Nusselt number obtained in some shallow enclosures is abnormally increased with the increase of power-law index.