(41d) A New Polydisperse Drag Law Derived from Lattice Boltzmann Simulations

We have performed extensive lattice Boltzmann simulations to obtain the drag force for random arrays of monodisperse and bidisperse spheres. For the monodisperse systems we studied 35 different combinations of the Reynolds number Re (up to Re=1000) and packing fraction, whereas for the bidisperse systems we also varied the diameter ratio (from 1:1.5 to 1:4) and composition, which brings the total number of different systems that we considered to 150. For monodisperse systems we find that our data is markedly different from the Ergun equation, and consistent with the correlation by Hill, Koch and Ladd which was based on similar type of simulations up to Re = 120. For bidisperse systems, we find that the correction of the monodisperse drag force for bidispersity, which was derived for the limit Re = 0, also applies for higher Reynolds numbers. On the basis of the data, we suggest a new drag law for general polydisperse systems which is on average within 10 % of the simulation data for Reynolds numbers up to 1000, and diameter ratio's up to 1:4. We have applied the new drag law in the larger scale discrete particle simulations of a binary fluidized bed. We find that with the our new drag relations the segregation rate is much closer to the experimental value, compared to the standard drag models.