Hydrodynamics Of Three-phase Fluidized Bed Research Articles

CFD study on hydrodynamics in three-phase fluidized beds—Application of turbulence models and experimental validation

CFD simulations of gas–liquid–solid fluidized beds have been performed in a full three-dimensional, unsteady multiple-Euler framework by means of the commercial software FLUENT. The simulation results were compared with experimental data obtained from laboratory scale three-phase fluidized beds. The significance of implementing accurate numerical schemes, as well as the choice of available k–ε turbulence models (standard, RNG, realizable), solid wall boundary conditions and granular temperature models were investigated. The results indicate that in order to minimize numerical diffusion artifacts and to enable valid discussions on the choice of physical models, third-order numerical schemes need to be implemented. The realizable turbulence formulation was unable to produce the expected solids gulf-stream pattern (i.e., rising solid particles in the core and descending solid particles near the wall) in three-phase fluidized beds whereas the RNG and standard k–ε models were able to better capture depictions of flow patterns. The best prediction of flow characteristics was obtained with a laminar model formulation accounting for the solid phase viscosity and the molecular viscosities of the two fluids.

Hydrodynamic studies on three-phase fluidized bed using CFD analysis

Three-phase fluidization refers to fluidization of solid particles by co-current, upward flow of gas and liquid-phases for the purpose of bringing three-phases in contact in a single operation. Due to complications in understanding hydrodynamics of three-phase fluidized bed, CFD analysis is used to predict the hydrodynamics of it. In this study, liquid-phase is water which flows continuously, where as the gas phase is air which is distributed discretely throughout the bed. Ceramic particle of 1 mm diameter, density of 2650 kg/m 3 is used as a solid phase. Excellent mixing, heat and mass transfer rates are the unique features of three-phase fluidized bed. The selection of distributor plays an important role in the quality of fluidization [1]. CFD model is created as the realistic representation of actual fluidized bed. The liquid and solid flow is represented by the mixture model. The air is injected from the bottom of the fluidized by means of discrete phase method (DPM). Simulation results are obtained by using porous jump and porous zone model to represent the distributor. It is found that porous zone model is best applicable in the industries, since stability of operating conditions is achieved even with non-uniform air, water flowrates and with different bed heights(100 mm, 200 mm, 300 mm, 400 mm and 500 mm). Simulated Pressure drop values of the fluidized bed have good agreement with the experimental findings. As the gas flowrate increases, the pressure drop in the column is decreases, provided the initial bed height, diameter of the column, and liquid flowrate are constant. This is due to decrease in density of the fluid medium in the bed by means of more gas hold up. The approach of the simulated values to the experimental values can be reduced with better understanding the nature of the fluidized bed.

Solid phase hydrodynamics of three-phase fluidized beds—A convective/dispersive mixing model

The main objective of this work was to develop a solid phase mixing model that followed not only the mixing extent, but also the overall mixing mechanism, i.e., the contribution of the convective onto the dispersive mixing mechanism. A non-invasive radioactive particle tracking (RPT) technique was used to estimate the model parameters and generate tracer curves at various axial positions. The proposed model follows the tracer data well compared to the axial dispersion model. It has the flexibility to represent various contributions of the convective onto the dispersive mixing mechanism observed in three-phase fluidized beds and it is linked to the bubble velocity distribution. The convective/dispersive model successfully followed the evolution of the extent of particle mixing and the overall mixing mechanism at various superficial gas and liquid velocities as well as reactor diameters.

Use of dimensional similitude for scale-up of hydrodynamics in three-phase fluidized beds

A new method of scaling three-phase fluidized beds is presented based upon achieving geometric and dynamic similitude with the aid of the Buckingham Pi theorem. This results in five dimensionless groups that must be matched to ensure hydrodynamic similarity between separate units. Experiments have been carried out to validate this technique by comparing gas hold-up and bed expansion in two different columns operating with significantly different fluid and solids properties, but where efforts have been made to match the five dimensionless groups. These comparisons show mostly favourable agreement between the two units.

Local particle-liquid heat transfer and hydrodynamics in three-phase fluidized beds with light particles

Local particle-liquid heat transfer and hydrodynamics in three-phase fluidized beds with light particles