Effects of fluidization velocity on solid stack volume in a bubbling fluidized-bed with nozzle-type distributor

CFD modeling of heat transfer and hydrodynamics in a draft tube conical spouted bed reactor under pyrolysis conditions: Impact of wall boundary condition

Slush nitrogen is a mixture of solid nitrogen particles and liquid nitrogen, and its flow characteristics in a horizontal pipe are investigated experimentally and theoretically in this study. Pressure drop of slush nitrogen is higher than that of subcooled liquid nitrogen due to the viscous and the mechanical frictions, and the dependence of pressure drop on the mean velocity varies under different flow conditions. The solid volume fraction distributions and the velocity throughout the pipe cross‐section of slush nitrogen flow are investigated with the Eulerian–Eulerian multiphase approach incorporated with the kinetic theory of granular flow. The flow patterns of slush nitrogen are determined as the pseudo‐homogeneous flow, the heterogeneous flow and the bedload flow from the experimental and numerical results. The relationship between the friction factor and the Reynolds number for slush nitrogen with various solid volume fractions is obtained by using the slush Reynolds number. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1762–1773, 2013

Parametric study of particles homogenization in cold-flow riser reactors

Based on the two-fluid model, a three-zone drag model was developed, and the kinetic theory of granular flows and the Schneiderbauer solids wall boundary model were modified to establish a new three-dimensional (3D) unsteady mathematical model for high-pressure dense-phase pneumatic conveying in horizontal pipe. With this mathematical model, the influence of the three frictional stress models, namely Dartevelle frictional stress model, Srivastava and Sundaresan frictional stress model, and the modified Berzi frictional stress model, on the simulation result was explored. The simulation results showed that the three frictional stress models accurately predicted the pressure drop and its variations with supplementary gas in the horizontal pipe, with relative errors ranging from −4.91% to +7.60%. Moreover, the predicted solids volume fraction distribution in the cross-section of the horizontal pipe using these frictional stress models exhibited good agreement with the electrical capacitance tomography (ECT) images. Notably, the influence of the three frictional stress models on the simulation results was predominantly observed in the transition region and deposited region. In the deposited region, stronger frictional stress resulting in lower solids volume fraction and a higher pressure drop in the horizontal pipe were observed. Among the three frictional stress models, the simulation results with the modified Berzi frictional stress model aligned better with the experimental data. Therefore, the modified Berzi frictional stress model is deemed more suitable for simulating high-pressure dense-phase pneumatic conveying in horizontal pipe.

Disengagement of dispersed cerium oxalate from nitric-oxalic acid medium in a batch settler: Measurements and CFD simulations

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

Multiphase modeling of settling and suspension in anaerobic digester

Gas leakage between reactors in a dual fluidized bed system

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

Fluidized beds are conventional components of many industrial processes, such as coal gasification for energy generation and syngas production. Numerical simulations help to properly design and understand the complex multiphase flows occurring in these reactors. Two modeling approaches are usually adopted to simulate multiphase flows: the two fluids Eulerian-Eulerian model and the continuous/discrete Eulerian-Lagrangian model. Since fluidized beds account for an extremely large number of particles, tracking each of them could not assure to get results within a reasonable computational time. The Computational Particle-Fluid Dynamics (CPFD) approach, which belongs to the Eulerian-Lagrangian models class, groups together particles with similar key parameters (e.g. composition, size) into computational units (parcels). Parcel collisions are modeled by an isotropic solid stress function, depending on solid volume fraction. In this paper, the bubbling fluidized bed (BFB) upstream gasifier of the EU research infrastructure ZECOMIX (Zero Emissions of Carbon with Mixed technologies) has been simulated using a CPFD approach via Barracuda® software. The effect of different fluidizing agent injection strategies on bed bubbling and mixing, for non-reacting cases, has been studied. The numerical results for a reacting case have been compared to the available experimental data, gathered during the coal gasification campaign. The model has proved to be very useful in the choice of the more efficient injection configuration that assures a more effective contact of the gas with the solid bed and a good bubbling fluidization regime, together with a satisfactory prediction of the outlet gas composition. The numerical approach has turned out to be robust and time-saving and allowed to dramatically reduce the computational cost with respect the classical two fluids Eulerian-Eulerian models. © 2018, Isfahan University of Technology.

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.

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

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.

This paper describes the numerical study on the effect of inlet air distribution in the Bubbling Fluidized Bed (BFB) riser of diameter 0.18 m and 1.44 m of length using a 3-hole orifice plate. A 2D model has been developed and meshed using Gambit software version 2.4.6 and was simulated using CFD code, fluent version 6.3. Laminar model has been used for the modeling and Eulerian-Eulerian multiphase model coupled with kinetic theory of granular flow was employed. For the drag, Gidaspow Drag Model was used to calculate the phase interaction between the gas and solid particles. The simulation results obtained for the validation purpose showed good agreement with the results available in the literature. The model with orifice plate gives a better and clear bubble shape with improved turbulent and better mixing compared to the model without the orifice plate. The model with orifice plate is also more realistic and ideal as compared to the model without the orifice plate.

Mixed convection in a lid-driven cavity filled with single and multiple-walled carbon nanotubes nanofluid having an inner elliptic obstacle