CFD simulation of multiphase fluid flow in a two-dimensional gas-solid fluidized bed using two different turbulence models

Computational fluid dynamics and experimental study of the hydrodynamics of a gas–solid tapered fluidized bed

CFD modeling to determine the minimum fluidization velocity of particles in gas-solid fluidized bed at different temperatures

In this work, the business Computational Fluid Dynamics (CFD) is used for the numerical simulations of an air-solid fluidized bed container in the solid phase involving a multi-fluid Eulerian multiphase model and the Kinetic Theory of Granular Flow (KTGF). The height of the fluidized bed setup is 1.5 m while its diameter is 0.2 m. With it, a series of experimentations were obtained using Helium tracer to determine the Residence Time Distribution (RTD) at various normalized velocities, that is, mixing of air-solids at different degrees. 2 and 3 dimensions of the fluidized bed container are simulated. The main purpose of this study is to understand the hydrodynamic behavior of air-solid fluidized bed container through a framework of Eulerian multiphase model and to analyze the hydrodynamic behavior of the air-solids mixing. As a first approach, the CFD model is validated using the experimental results of the residence time study. The numerical results of RTD corresponded well with the experimental findings. This shows that the CFD modeling might be used to indicate the performance of a fluidized bed reactor. Key words: Computational fluid dynamics, fluidized bed, residence time distribution (RTD), gas-solids mixing, turbulence.

The flow behaviour of a lab-scale fluidised bed with a central jet has been simulated. The study has been performed with an in-house computational fluid dynamics (CFD) model named FLOTRACS-MP-3D. The CFD model is based ona multi-fluid Eulerian description of the phases, where the kinetic theory for granular flow forms the basis for turbulence modelling of the solid phases. A two-dimensional Cartesian co-ordinate system is used to describe the geometry. This paper discusses whether bubble formation and bed height are influenced by coefficient of restitution, drag model and number of solid phases. Measurements of the same fluidised bed with a digital video camera are performed. Computational results are compared with the experimental results, and the discrepancies are discussed.

High energy consumption in fluidized bed dryers (FBDs) remains a critical challenge for tea processing, largely due to poor fluidization quality of sticky, irregular, and non-uniform tea particles. To address this issue, this study investigated the potential of horizontal-axis rotary agitators to improve the hydrodynamics of a gas-solid FBD and reduce energy losses. Computational fluid dynamics (CFD) simulations were performed using the two-fluid model combined with the kinetic theory of granular flow (TFM-KTGF), focusing on key parameters including pressure drop, standard deviation of pressure drop, solid volume fraction distribution, and granular temperature. Some configurations were analyzed: a bed without an agitator, and beds equipped with rotary agitators of varying blade numbers (three and five) and diameters (200 mm and 300 mm) at different rotational speeds. The results demonstrated that introducing a horizontal-axis rotary agitator significantly improves fluidization. The largest rotary domain (five blades, 300 mm diameter) achieved the lowest pressure drop of 315,135 Pa at 6.28 rad/s, while also promoting more uniform solid distribution and increasing granular temperature up to 2.5 × 10⁻ 3 J/kg. The agitator enhanced particle circulation, expanded lean regions within the bed, and reduced dense packing, leading to improved gas-solid contact and reduced resistance to airflow. Furthermore, increasing the agitator speed decreased pressure drop and its standard deviation, while increasing the granular temperature, confirming the beneficial effect of enhanced stirring energy. This study highlights the effectiveness of horizontal-axis rotary agitators in enhancing the hydrodynamic performance of FBDs, offering a promising approach to improve energy efficiency and drying uniformity in tea production. The insights presented here can guide future design and optimization of industrial-scale dryers handling cohesive, irregular particles.

Determination of minimum fluidization velocity in fluidized bed at elevated pressures and temperatures using CFD simulations

Effect of flow pulsation on fluidization degree of gas-solid fluidized beds by using coupled CFD-DEM

Fundamental particle fluidization behavior and handling of nano-particles in a rotating fluidized bed

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

Hydrodynamic characteristics of a gas−liquid−solid conical fluidized bed were studied and compared with both liquid−solid conical beds and three-phase cylindrical fluidized beds. The effect of bubbles on particle mixing, pressure drop, and minimum fluidization velocity were discussed. Minimum fluidization velocities predicted by modified Ergun equation which accounts for the variation of the cross-sectional area with the bed height were found to be in good agreement with the liquid−solid conical fluidized bed data. The models of Song et al. [Can. J. Chem. Eng. 1989, 67, 265] and Zhang et al. [Power Tech. 1998, 100, 113; PhD. Thesis, 1996], derived originally for three-phase cylindrical fluidized beds, respectively, were modified for the prediction of Umf in a three-phase conical fluidized bed by accounting for the geometrical variation of the conical bed. It is found that the modified Song et al. model gave a better agreement than the modified Zhang et al. model in comparison with the current experimental data. However, the prediction of the modified Zhang et al. model is much improved when the parameter α, fractional gas holdup, was estimated using the equation from the Song et al. model.

Numerical analysis of liquid-solid flow in tapered and cylindrical fluidized beds for wastewater treatment and biogas production

Computational fluid dynamics (CFD) is an important and effective tool to study the airflow field and contaminant distribution in aircraft cabins. The accuracy of numerical simulation using the CFD approach could be significantly affected by configurations of the inlet boundary conditions, turbulence model, etc. The core of this study was to assess whether conclusions achieved in simulation of airflow on usual surfaces in buildings like in commercial offices could be applicable to aircraft cabins. Comparative studies involving turbulence models or air supply opening models in aircraft cabin environment are still absent in the literature. Therefore, in this study, two turbulence models (the renormalization group (RNG) k-ɛ model and Reynolds-stress model) and three types of air supply opening models (simple open model, basic model and momentum model) were applied to simulate the airflow and contaminant concentration fields in a mockup seven-row cabin section. Our simulation results were compared with the experimental data. Six indexes based on different criteria were used to quantitatively evaluate the agreement between measurements and modelled results given by turbulence models and air supply opening models. The results show that the RNG k-ɛ and RSM turbulence models have similar accuracy in airflow and contaminant fields in the mockup cabin, and the momentum model has the best accuracy among the three air supply opening models for the aircraft cabin environment.

Supercritical water fluidized bed is a promising reactor which can realize the efficient and clean gasification of coal to produce hydrogen. As the high pressure and temperature inside supercritical water fluidized bed, the study of the detail flow behaviors needs the help of numerical method. Considering the limitation of the two-fluid method and discrete element method, the computational particle fluid dynamics method was applied to this work. When particle size distribution was taken into consideration, the simulated results showed that the transformation from fixed bed regime to fluidized bed regime is a gradual process. With the increase in superficial fluid velocity, particles in small diameter migrate to the top of the bed and there exits layering phenomenon in the bed. Besides, though the particles are categorized as Geldart B group, the minimum fluidization velocity is not equal to the minimum bubbling fluidization velocity and there is a complicated bed expansion process after incipient fluidization. The bed expansion process is also influenced by the particle size distribution.

The effects of an apartment complex on flow and pollutant dispersion in an urban area are numerically investigated using a computational fluid dynamics (CFD) model. The CFD model is based on the Reynolds-averaged Navier-Stokes equations and includes the renormalization group k- turbulence model. The geographic information system (GIS) data is used as an input data of the CFD model. Eight numerical simulations are carried out for different inflow directions and, for each inflow direction, the effects of an apartment complex are investigated, comparing the characteristics of flow and dispersion before and after construction of the apartment complex in detail. The observation data of automatic weather system (AWS) is analyzed. The windrose analysis shows that the wind speed and direction after the construction of the complex are quite different from those before the construction. The construction of the apartment complex resulted in the decrease in wind speed at the downwind region. It is also shown that the wind speed increased partially inside the apartment complex due to the channeling effect to satisfy the mass continuity. On the whole, the wind speed decreased at the downwind region due to the drag effect by the apartment complex. As a result, the passive pollutant concentration increased (decreased) near the downwind region of (within) the apartment complex compared with that before the construction.

The hydrodynamics and heat transfer of a gas-solid fluidized bed chamber was investigated by computational fluid dynamic (CFD) techniques. A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this chamber. For momentum exchange coefficients, Syamlal-O’Brien drag functions were used. A suitable numerical method that employed finite volume method was applied to discretize the equations. The simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Also, the solid particle temperature effect on heat transfer and hydrodynamics was studied. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops and mean gas temperature predicted by the simulations at different positions in the chamber were in good agreement with experimental measurements at gas velocities higher than the minimum fluidization velocity. Furthermore, this comparison showed that the model could predict hydrodynamics and heat transfer behaviors of gas solid fluidized bed reasonably well.