3D numerical study on the influence of particle porosity on heat and fluid flow

This work is devoted to the three-dimensional numerical simulations of the heat and fluid flow past and through a porous spherical particle over a wide range of Reynolds numbers (20 < Re < 500) corresponding to the steady-state flow and different values of porosity varying between 0.62 and 0.92. The porosity of a particle is modelled using two approaches corresponding to a microscopic and macroscopic representation of the pores, respectively. Specifically, in the first approach the porous particle is represented by a cluster of small spherical particles distributed inside the porous particle. The second approach represents the porosity implicitly utilising the so-called permeability model, adopting the Blake-Kozeny equation to treat the fluid and heat flow inside a particle. The comparison of the two models showed good agreement for a porosity below 0.7. The analysis of numerical simulations showed that for a constant Reynolds number (Re < 100), with increasing porosity, the value of the drag coefficient decreases slightly. However, when the Reynolds number is increased (Re > 100) a local maximum in the drag force coefficient was observed for a porosity of about 0.76. On the basis of the results of simulations, expressions are derived and examined for the drag coefficient and the surface-averaged Nusselt number.