Recent developments in experimental (PIV) and numerical (DNS) investigation of solid–liquid fluidized beds

Abstract

Particle image velocimetry measurements have been performed in a solid–liquid fluidized bed in the Reynolds number range 51–759. To do this, the refractive indexes of the solid and liquid phases were matched at approximately 1.47 using 3mm diameter borosilicate glass beads and a solution of turpentine and tetra-hydronaphthalene. Paraffin oil was added in varying quantities to vary the dynamic viscosity between 0.0012 and 0.010Pas without changing the refractive index of the solution. From the PIV measurements, at sampling rates of 2Hz, the fluctuating velocity components were found to be quite uniform in both the axial and radial directions. Moreover, the computed turbulent kinetic energy dissipation rates were also found to be relatively constant throughout the bed, thus highlighting the homogenous nature of the turbulence within the system.Following from Reddy et al. (2010b), direct numerical simulations were undertaken at particle Reynolds numbers up to 200 for assemblages of 1, 9, 27, 100, 180 and 245 particles, which corresponded to a liquid volume fraction range of 0.687<∈L<0.998. The effect of surrounding particles on the settling velocity (hindrance effect) and the wake dynamics was investigated. It was found that the average settling velocity decreased with an increasing number of particles, with the quantitative results being in good agreement with the well established empirical correlation of Richardson and Zaki (1954). The local energy dissipation rate was also computed, and for a particle Reynolds number of 51, it was found to be 5.5m2s−3. This value was approximately 18 times the average energy dissipation rate of 0.30m2s−3; and compared favourably with the 0.36m2s−3obtained by a volume-averaged energy balance of the experimental system.