CFD–PBM Simulation on Bubble Size Distribution in a Gas–Liquid–Solid Flow Three-Phase Flow Stirred Tank

Abstract

The bubble size distribution, location distribution, and gas holdup in a gas–liquid–solid flow three-phase stirred tank were numerically simulated by the Eulerian–Eulerian method and the population balance model (PBM). The Euler–Euler method combined with the PBM model included the influence of bubble aggregation and fragmentation on the interfacial force, which can better predict the bubble size distribution and phase holdups. The simulation results show that there are some differences in the fluid morphology and gas dispersion characteristics in the stirred tank under different rotating speeds. With the increase of rotating speed, the content of small-diameter bubbles increases obviously, and they are mainly concentrated in areas with higher speeds. The higher the rotational speed, the more the bubbles with small diameters, but the content of bubbles with large diameters is less affected by the rotational speed. Small-size bubbles mainly exist in the region of high fluid velocity, while large-size bubbles mainly exist in the region of low hydrostatic pressure. Compared with the change of the bubble content at different speeds, the content of bubbles with diameters of 0.50–1.90 mm is largest at 2000 rpm, while the content of bubbles with diameters of 2.65–10.09 mm is largest at 1500 rpm. The simulation work has certain guiding significance for the research and development of the forced mineralization device and the understanding of the dispersion characteristics of bubbles in the stirred tank.

Hydrodynamic Characteristics of a Stirred Tank with Self‐Priming Jet Impeller

“…The realizable k-e model [15][16][17][18] layer was solved by the standard wall function. Water was used as continuous-phase medium; the density is 998.2 kg m -3 and the viscosity is 1.003 mPa s. The rotating zone was set as the rotating reference frame, the rotating axis is the positive z-axis, and the origin of the coordinate system was at the center of the stirred-tank bottom.…”

“…The three‐dimensional steady‐state simulation method was used to solve the fluid flow problem. The realizable k‐ε model 15–18 was adopted to calculate the turbulence flow, and the boundary layer was solved by the standard wall function. Water was used as continuous‐phase medium; the density is 998.2 kg m −3 and the viscosity is 1.003 mPa s. The rotating zone was set as the rotating reference frame, the rotating axis is the positive z ‐axis, and the origin of the coordinate system was at the center of the stirred‐tank bottom.…”

Design and Optimization of Gas–Liquid Vortex Unit Using Computational Fluid Dynamics (CFD) Simulation

“…Detailed discussions and descriptions of the Eulerian–Eulerian two-fluid model can be found in various recent publications. ,,− Therefore, only a brief summary of the most relevant equations to be solved is given. Assuming that gas and liquid are incompressible and immiscible, the mass conservation equation for phase q is ∂ ∂ t false( α q ρ q false) + ∇ · false( α q ρ q u q → false) = 0 where α q , u q → , and ρ q are the volume fraction, velocity, and density of fluid phase q (i.e., liquid or gas), respectively.…”

Investigation of the Gas–Liquid–Solid Stirred Tank by Using the Intrusive Image-Based Method

“…Figures 4 and 5 present the statistical analysis of the probability density function (PDF) of bubbles, revealing the variation of the bubble size distribution with the solid concentration in terms of the bubble number fraction and bubble volume fraction, respectively. In Figure 4, the shape of the BSD varies significantly with the measurement position, but it is more or less similar at the same radial position, which is consistent with the results in gas−liquid stirred tanks by Senouci-Bereksi et al 2 and Li et al 42 The peak value of the bubble size is mainly concentrated in the range of 0.25−0.75 mm when the radial position (r/R = 0.3) is close to the impeller shaft, and it will shift to 0.75−1.75 mm at the radial position (r/R = 1.0) close to the tank wall. Upon comparing Figure 4(a,c), it can be observed that the bubble size distribution near the impeller shaft shows a bimodal distribution with the increase of the gas flow rate.…”