Experimental and numerical study of fluidization and pressure drop of spherical and non-spherical particles in a model scale fluidized bed

Experimental Study on the Agglomeration Behavior of Elongated Biomass Particles in a Lifting Tube

Pneumatic conveying devices are commonly used in the fields of chemical industry, raw material transportation, and material processing. Elongated biomass particles are not evenly distributed in the lifting tube because biomass clumps during conveying. Pneumatic conveying test setup and measurement system were built in this paper in order to study the agglomeration behavior of elongated biomass particles in the lifting tube experimentally. Particle tracking velocimetry (PTV) was used to determine the area distribution and velocity distribution of particles at different apparent air velocities and mass flow rates. The results show that while keeping the mass flow rate constant at 46.50 g/s, the apparent gas velocity increased from 5.91 to 7.91 m/s and the maximum size of agglomerates decreased from 0.689 to 0.235. The apparent gas velocity was kept at 6.40 m/s, and the particle mass flow rate was adjusted from 56.50 to 16.20 g/s. The maximum size of the agglomerates was reduced to 0.115. Therefore, appropriately increasing the apparent gas velocity or decreasing the particle mass flow rate can improve the uniformity of the particle distribution in the lifting tube. The results would provide a reference for parameter adjustment of pneumatic conveying devices in industrial production.

Development of a Model for the Separation Characteristics of a Deflector Wheel Classifier Including Particle Collision and Rebound Behavior

Deflector wheel classifiers are widespread in industry for the separation of powders into fine and coarse powders. Even though this separation process has been known for quite some time, it is not yet fully understood, and existing models fail to precisely predict the separation characteristics. Due to the high throughput of deflector wheel classifiers, it is greatly beneficial to estimate the separation characteristics before the experiment. Here, the developed model critically examines the usual assumptions, such as ideal airflow, neglection of particle–wall and particle–particle interactions, or spherically-shaped particles. First, the investigation of the air flow using a Particle Image Velocimetry (PIV) system showed significant differences to the assumed ideal flow field, then particle sphericity and its influence on the interaction between the particles and the paddles of the deflector wheel was investigated and compared with particle rebound behavior on a static wall. Surprisingly, comminuted glass behaves similarly to comminuted limestone in multiple aspects and not like glass beads. To determine the number of particle–particle collisions, Discrete Element Method (DEM) simulations were performed. The aforementioned aspects found application in the model and the separation behavior was well-estimated.

Impact of Particle Shape and Surface Group on Membrane Fouling

Membrane fouling remains one of the most critical drawbacks in membrane filtration processes. Although the effect of various operating parameters—such as flow velocity, concentration, and foulant size—are well-studied, the impact of particle shape is not well understood. To bridge this gap, this study investigated the effect of polystyrene particle sphericity (sphere, peanut and pear) on external membrane fouling, along with the effect of particle charge (unmodified, carboxylated, and aminated). The results indicate that the non-spherical particles produce higher critical fluxes than the spherical particles (i.e., respectively 24% and 13% higher for peanut and pear), which is caused by the looser packing in the cake due to the varied particle orientations. Although higher crossflow velocities diminished the differences in the critical flux values among the particles of different surface charges, the differences among the particle shapes remained distinct. In dead-end filtration, non-spherical particles also produced lower flux declines. The shear-induced diffusion model predicts all five particle types well. The Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (XDLVO) models were used to quantify the interaction energies, and the latter agreed with the relative critical flux trends of all of the PS particles. As for the flux decline trends, both the DLVO and XDLVO results are in good agreement.

Hydrodynamics of Irregular-Shaped Graphite Particles in Coaxial Two-Phase Jet Flow

Expanded graphite particle is characterized by the low density in comparison with those of bead glass and copper particles. Hydrodynamics of the irregular-shaped graphite particle swirling flows in a coaxial chamber are investigated via an improved kinetic frictional stress model. A drag force coefficient considering the effects of irregular shapes based on the artificial neural network algorithm is adopted to describe the momentum transfer between nonspherical particles and gas phases. The proposed model, algorithm, and source code for modeling and simulation are validated by measurement using spherical glass beads, and acceptable agreement is obtained. Lower sphericity particles enhance the anisotropic particle dispersions and induces the redistributions of the Reynolds stresses of the two-phase flow. Irregular-shaped particles are more sensitive to the gas followability instead of own inertia, whereas spherical particles are easier to be affected by the inlet effects. The interlock force between nonspherical particles takes great effect on particle flow than the spherical particle. The axial-axial normal stresses of sphericities of 0.63 and 0.72 are approximately 3.4 times larger than those of shear stress of spherical particle, and their axial velocities locating at near central regions are 3.0 times larger than those of sphericities.

Fluidization of elongated particles-Effect of multi-particle correlations for drag, lift, and torque in CFD-DEM

Having proper correlations for hydrodynamic forces is essential for successful CFD-DEM simulations of a fluidized bed. For spherical particles in a fluidized bed, efficient correlations for predicting the drag force, including the crowding effect caused by surrounding particles, are already available and well tested. However, for elongated particles, next to the drag force, the lift force, and hydrodynamic torque also gain importance. In this work, we apply recently developed multi-particle correlations for drag, lift and torque in CFD-DEM simulations of a fluidized bed with spherocylindrical particles of aspect ratio 4 and compare them to simulations with widely used single-particle correlations for elongated particles. Simulation results are compared with previous magnetic particle tracking experimental results. We show that multi-particle correlations improve the prediction of particle orientation and vertical velocity. We also show the importance of including hydrodynamic torque.

Effect of particle shape on bubble dynamics in bubbling fluidized bed

Particle shape can significantly affect the bubble dynamics of bubbling fluidized beds (BFB). In this paper, findings obtained from simulations using CFD-DEM are summarized to discuss the effect of particle shape on bubble dynamics and bubble properties such as bubble size, shape and velocity at a single orifice and uniform fluidized bed. Particles with aspect ratios at 0.5 (oblate), 1 (spherical) and 2 (prolate) are employed to represent disc-like, spherical and rod-like particles, respectively. Both single jet and uniform fluidized bed simulations demonstrate that the bubble forming/rising regions, bubble coalescence locations, and bubble splitting phenomena are significantly influenced by particle shape. The CFD-DEM results for bubble size and bubble velocity show good agreement with literature correlations.

CFD-DEM -DDM Model for Spray Coating Process in a Wurster Coater

A multiscale model by coupling computational fluid dynamics (CFD) with a discrete element model (DEM) and discrete droplet model (DDM) is developed to simulate a lab-scale Wurster coater. Two case studies are conducted to study the effect of particle shape in the system. In the first case study, 45,000 spherical particles are coated for 5 s while for the second case study, a mixture of 22,500 spherical particles and 22,500 cylindrical particles is simulated. The residence time distributions (RTD) of particles in different spray zones are compared, and the best spray zone is derived by analysing the positions of spray droplet-particle contacts. The simulation results show that the RTD of the particles within an accurate spray zone can provide valuable information on the final product's particles size distribution. Furthermore, the coefficient of variation (COV) for the coating mass received by the particles is studied for both case studies.