Numerical simulation of flow behavior of particles in a gas-solid stirred fluidized bed

The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Grober equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

Multiphase modeling of settling and suspension in anaerobic digester

Simulations of flow behavior of particles in a liquid-solid fluidized bed using a second-order moments model

Hydrodynamics of dense gas-solid flows is investigated computationally using Euler-Euler methodology. The method used is primarily based on the kinetic theory of granular flow (KTGF) and additionally by incorporating the features of frictional pressure models (FPM). Frictional stresses are accounted when solid volume fraction reaches the frictional packing limit (FPL). Investigations on the effects of bed pressure drop and other gas-solid flow characteristics have revealed that a value for frictional packing limit around 0.61 yields better results. It is also found that the FPM affects the bed hydrodynamics up to a superficial gas velocity of around 1.5 times the minimum fluidisation velocity. The numerical results of bed pressure drop and bed expansion ratio are validated against the corresponding experimental data available in literature. Detailed velocity and voidage profiles are reported along with the contours of solid volume fraction, and velocity vectors of gas and solid phases.

Modification of kinetic theory of granular flow for frictional spheres, part II: Model validation

Batch kinetic study of sorption of methylene blue by perlite

Flow behavior of particles is simulated by means of discrete element method (DEM) in a screw conveyor. The gas flow is considered by the Euler model. The subgrid scale model turbulence model is applied to solve gas turbulence. A detailed description of the model equations applied has been presented. The comparison between computational fluid dynamics (CFD)‐DEM (i.e., considering gas flow) and DEM (i.e., not considering gas flow) simulation results is performed. Predicted mass flow rate with CFD‐DEM model is in better agreement with experiments by Roberts and Wills comparing with DEM results. The effects of incline angle and filling rate on the flow behavior of particles are predicted. The simulation results show that the gas flow has a major impact on particle flow behavior at a high rotation speed, whereas the velocity of particles increases with an increase of rotation speed. As the filling rate rises, both the translational granular temperature and the rotational granular particle temperature decline, which means that the particles fluctuation turns weak. While with an increase of incline angle, from the horizontal to vertical, the translational granular temperature is increased, but the rotational granular temperature reduces and then goes up. In brief, translational motion is a main mode of motion in a screw conveyor.

The granular pressure and granular temperature underpin various models of granular flows while they are playing an increasing role in modeling of other phenomena in granular systems such as heat transfer, segregation, erosion, attrition, and aggregation. The development and validation of these theories demand experimental determination of these two quantities. Diffusing wave spectroscopy (DWS) is now an accepted technique for measurement of granular temperature in dense granular systems. Using granular temperature data obtained from DWS with the kinetic theory of granular flow, we have derived the granular pressure data for a liquid‐fluidized bed. The determined variation of the mean bed granular pressure with mean bed solid volume fraction compares favorably with previously published experimental data and theoretical models of others. Where discrepancies do occur, they may be attributed to differences in particle inertia, suggesting further work on granular pressure models is required. Finally, we report the variation of the granular pressure with height above the distributor for several mean solids volume fractions. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Numerical study on liquid-solid flow characteristics in inverse circulating fluidized beds

Numerical simulation of gas–solid flow with two fluid model in a spouted-fluid bed

Effect of agitation on the characteristics of air dense medium fluidization

CFD simulation of an agitated gas-fluidized bed: Effects of particle–particle restitution coefficient on the hydrodynamics

Biosorption of chromium (VI) from aqueous solutions by the husk of Bengal gram (Cicer arientinum)

ABSTRACTIn this paper, numerical and experimental analyses of the heat transfer between an immersed heater and a cone bed of sand particles were carried out. A three-dimensional (3D) model using the Eulerian–Eulerian model coupled with the kinetic theory for granular flow was used to simulate heat transfer and the related bed flow characteristics. The effects of different inlet gas velocities, represented by the fluidizing number (the ratio between inlet gas velocity to minimum fluidizing velocity), and different particle-wall boundary conditions on heat transfer and hydrodynamics were investigated. Both the experiments and numerical simulation results showed that the heat transfer coefficient and the bed expansion ratio increased with increasing the inlet gas velocity. For the particle-wall boundary condition, applying the no-slip condition showed the best agreement in the heat transfer coefficient and the bed expansion ratio to the experimental results.

Numerical simulation of flow behavior of particles in a porous media based on CFD-DEM