Lattice Boltzmann simulation of TiO2-water nanofluid in a curved boundary domain at high Rayleigh numbers

In this paper, a lattice Boltzmann method has been utilized to simulate the natural convection of TiO2-water nanofluid in a curved geometry. The effect of Rayleigh number, volume fraction of nanoparticles, size of nanoparticles and boundary conditions on the average Nusselt number have been studied numerically. A two component model has been used to consider the interaction forces between nanoparticles and the base fluid. In this way, the effect of nanoparticle size can be considered. The natural convection has been simulated in a cavity with two curved boundaries. The aspect ratio, ratio of the diameter of the curved boundaries to the total height, is chosen to be 0.33. Two different thermal boundary conditions, namely adiabatic and constant temperature, have been considered in the current work for the curved boundaries. The Rayleigh number varies from 103 to 109. The size effect of nanoparticles has also been considered through interaction forces and four different sizes namely 10, 25, 65 and 90nm, have been chosen for nanoparticles. Results show that the enhancement in Nusselt number by adding nanoparticles (Nu*) increases with the increase in and Rayleigh number and the decrease of nanoparticle diameter. Results also show that increasing volume fraction increases viscosity which in higher values of might reduce Nu*. Furthermore, the effect of boundary condition on the improvement of Nusselt number due to presence of nanoparticles has been investigated. The method is also shown to have higher convergence rate than the traditional computational methods.

Keywords:

Lattice Boltzmann method , High Rayleigh number , curved boundary , nanofluid , natural convection