Behavior Of Solid Particles Research Articles

Three-Dimensional Visualization Of The Behavior Of Solid Particles Traveling In A Horizontal Gas Pipe Flow By Color PTV Using Discontinuously Changing Hue Illumination

In a gas pipe, a lot of solid particles remained during its construction. They are called dust and gas supply companies have tried to remove them using filters because they cause various problems. To optimize the maintenance period of dust removal filters, it is required to understand the behaviors of particles in the pipe. However, we do not fully understand yet because of their very complex behaviors caused by dune accumulated in the pipe. Furthermore, it is hard to investigate their behaviors with a traditional volumetric PTV using multiple cameras. Normally, its calibration is difficult because of the curvature of the pipe and the plural number of cameras. Therefore, we developed a new volumetric color PTV algorithm with discontinuously changing color illumination in the camera shooting direction, i.e. the depth direction. Color PTV can determine particle positions in three dimensions using a single camera but has low depth accuracy. Our new PTV measures particle positions and velocity vectors in the plane of picture using the same algorithm used in the normal planar PTV. On the other hand, particle positions and velocity vectors in the camera shooting direction are measured by a pattern of color changing on particle scattering light, which is our original method. To adopt the new volumetric PTV in the pipe flow, a volumetric light changing color discontinuously in the flow direction was irradiated and the particles were visualized using a camera installed at the outlet of the pipe. When a dune exists, the particles are thrown to the top of the pipe and their advection velocity is increased by the wakes generated by the dune. As a result, the dune makes more particles to be advected to a longer distance.

Numerical investigation on solids settling in a non-Newtonian slurry inside a horizontal flume

Slurry transportation is always crucial for many industrial processes. This study numerically investigates the settling behavior of multisize solid particles in a non-Newtonian slurry inside a semicircular open channel (flume). The non-Newtonian slurry is modeled using a three-dimensional unsteady Eulerian–Eulerian (E–E) model coupled with the Hershel–Bulkley rheological model. A detailed sensitivity analysis of drag models is performed to establish the solid–fluid interaction in the slurry flow. The numerical model is validated with the experimental data from the literature and shows a fair agreement. The validated model is used to simulate the settling behavior of the slurry in the flume. The mean particle diameter of the solid particles in the slurry is in the range of 75–296 μm with a median diameter of 188 μm. The effect of particle size distributions (PSDs), flume inclination, bubble size, and bubble volume fraction on the particle settling inside the flume is investigated in the parametric study. The analysis of our results revealed that the settling of solids is significantly affected by PSDs in the open channel system. In particular, the increase in flume inclination progresses the settling and dissipation of fine and coarse particles, respectively. Additional simulations showed that the inception of bubbles influences the settling velocity of solids, which changes the settling behavior of multisize solids inside the flume. The presented study can be used as a valuable guideline for the optimization of intermediate exclusion of water from thickened slurry in order to ensure the stability of tailing storage facility.

Effect of vibration and airflow on separation of 6–1 mm fine coal in compound dry separation bed

The segregation behaviour of solid particles are affected by airflow and vibration in a compound dry separation bed. The distribution characteristics of airflow field on the bed surface have been systematically investigated by a novel method of regional air distribution, and the movement and segregation behavior of fine coal particles have been observed under different gas velocity. Meanwhile, the spatial distribution characteristics and ash variation of fine coal particles during the process of segregation and stratification were analyzed. The obtained results show that the airflow velocity of the bed showed a zonal air distribution characteristic of gradual decrease from the separation area to the clean coal section and the gangue section. The segregation and stratification of particles in the Y-axis and Z-axis directions of the bed surface can be enhanced by vibration. When the vibration frequency is 34 Hz, the probable error (E) is 0.08 g/cm3. The bed inclination and the bed grid height have a certain influence on the segregation behavior of fine coal.

Trajectory dynamics of particles in accelerated toroidal pipe: A computational study using CFD-DPM simulations

In this study, we investigate the behavior of solid particles of varying sizes within an accelerated toroidal filled with fluid using computational fluid dynamics- discrete phase model (CFD-DPM) simulations. A comprehensive grid independence study and validation were conducted to ensure the accuracy of our simulations. We focus on particles with 10-, 50-, and 100-microns diameters. Our simulations indicate that the primary flow (relative tangential velocity) of both the fluid and the particles follow the input acceleration. We also examined the secondary flow within the toroidal. Smaller particles (10 microns) closely follow the fluid flow with minimal lag, while larger particles (50 and 100 microns) exhibit a noticeable lag due to the inertia effect. Furthermore, the displacement from the initial position is also dependent on the particle size, with smaller particles traveling further distances. However, despite the ongoing acceleration of the fluid and the toroidal, the largest particles (100 microns) eventually settle and stop due to their high inertia (mass), and their velocity begins to decrease during the acceleration of the toroidal. These findings highlight the significant role of particle size in determining particle behavior within a toroidal, paving the way for future research and Particle Imaging Velocimetry Gyroscope (PIVG) application.

N-Euler mathematical modelling and numerical simulation of liquid–gas–solid flows

Three phase flows are omnipresent in industrial as well as natural configurations. Understanding the behaviour of solid particles interacting with liquid–air flows can be of great interest for both topics. In this paper we present a new liquid–gas–solid modelling technique based on the hybrid method combining liquid–gas two-fluid phase-average approach and probability density function (PDF) methods for solid dispersed phases. The PDF approach is based on single particle dynamic equation taking into account its interaction with more than one fluid and separate stochastic Lagrangian equations for each fluid phase velocity seen by the particles. This method does not assume the carrier phases typology. The solid particles can interact with bubbles, droplets, pockets and stratified flow through drag only (other interaction forces are supposed to be negligible for our cases). In this work, it is assumed that the total drag applied to the particle is a linear combination of the drags computed if the particles were interacting separately with each fluid phases. Finding the linear combination coefficient represent the main modelling step. Particle collisions and particle turbulent dispersion are taken into account in the model. Dispersed bubbles can undergo coalescence and fragmentation. The effect of all these sub-models is studied in the comparison with experimental data.The fluid and particle equations are first derived before introducing the appropriate coupling terms. Then, the closure terms for turbulence and multiphase drag are introduced. The model is implemented in neptune_cfd, a finite volume solver developed by EDF, CEA, IRSN and Framatome which allows for the numerical resolution of separate Eulerian equations (mass, momentum and energy) for n phases coupled by interfacial transfer terms. The model is then compared against experimental data obtained in a bubble column charged with particles. The results obtained with it are satisfactory and enable us to study more in details its hypothesis and to confirm comments made in the first section. Eventually, the model is tested on an industrial case which shows its efficiency.

Improved prediction of settling behavior of solid particles through machine learning analysis of experimental retention time data

The motion of particles through density-stratified interfaces is a common phenomenon in environmental and engineering applications. However, the mechanics of particle-stratification interactions in various combinations of particle and fluid properties are not well understood. This study presents a novel machine-learning (ML) approach to experimental data of inertial particles crossing a density-stratified interface. A simplified particle settling experiment was conducted to obtain a large number of particles and expand the parameter range. Using ML, the study explores new correlations that collapse the data gathered in this and in previous work by Verso et al. (2019). The “delay time”, which is the time between the particle exiting the interfacial layer and reaching a steady-state velocity, is found to strongly depend on six dimensionless parameters formulated by ML feature selection. The data shows a correlation between the Reynolds and Froude numbers within the range of the experiments, and the best symbolic regression is based on the Froude number only. This experiment provides valuable insights into the behavior of inertial particles in stratified layers and highlights opportunities for future improvement in predicting their motion.

Effect of Inserting Baffles on the Solid Particle Segregation Behavior in Fluidized Bed Reactor: A Computational Study

In multi-solid, particle-size fluidized bed reactor systems, segregation is commonly observed. When segregation occurred, small solid particles were entrained to the top of the bed and escaped from the reactor. During the combustion process, the small solid particles that escaped from the boiler were burned and subjected to damage around the cyclone separator. This study then employed a computational fluid dynamics approach to investigate solid particle behavior in the reactor using three different sizes of solid particles. The effects of baffle insertion, baffle angle, stage number, and its arrangement were examined. The percentage of segregation was calculated to compare behavior among different reactor systems. The insertion of 45-degree baffles resulted in reduced segregation behavior compared to cases without baffles and with 90-degree baffles, attributed to solid hindering and collision phenomena. Additionally, a double-stage baffle with any arrangement could reduce segregation behavior. The best arrangement was “above-arrangement” due to particles hindering, swirling, and accumulating between the baffle stages. Therefore, to diminish segregation behavior and enhance combustion chemical reactions, the insertion of baffles in the reactor zone is recommended.

Propagation and attenuation of acoustic in gas-solid fluidized beds of group B particles

The introduction of an acoustic field can change the hydrodynamic behavior of solid particles in gas-solid fluidized beds, and in turn, the quasi-fluid in fluidized beds affects the acoustic propagation characteristics, such as the attenuation of acoustic waves in the fluidized-bed particle swarm. In this work, we investigated the transmission and attenuation process of sound waves in the fluidized bed of group B particles in the acoustic frequency range from 50 to 500 Hz. The obtained results show that there are three different attenuation stages during the propagation of acoustic waves through the fluidized bed with group B magnetite powder particles. The sound pressure level distribution model is extended to the sound-assisted fluidization of group B particles, and the prediction of the transmission and attenuation process of sound waves in the fluidized bed is in good agreement with the experimental values with an error below 5%.

Eulerian–Lagrangian fluid dynamics study on the effects of inlet radial angle on the performance and flow pattern of multi-inlet cyclone separator

This paper presents a study on the influence of inlet radial angle in a multi-inlet cyclone separator using Eulerian-Lagrangian (EL) fluid dynamics approach. The investigation focuses on the behavior of air and solid particles within the cyclone. Air circulation was simulated at velocities ranging from 2 to 6 m/s, with inlet radial angles of 15°, 32°, 45°, 61°, and 72°. To model the turbulent flow, the Reynolds stress model (RSM) and renormalization group k-model (RNG) were employed, while the particle trajectories were simulated using the discrete phase model (DPM) in ANSYS Fluent. The purpose of this study was to determine how the inlet radial angle impacts various parameters: collection efficiency, pressure drop, cut-off diameter, axial velocity, and tangential velocity. The numerical data obtained from the simulations were validated and found to be consistent with the existing literature. The results revealed interesting findings. In the case of an inlet velocity of 6 m/s, the highest pressure drop of 84.5 Pa was observed for the 15° inlet radial angle, while the lowest pressure drop of 77.42 Pa was observed for the 32° inlet radial angle. It was found that the collection efficiency varied according to the radial angle of the inlet, with values of 89.00%, 91.70%, 92.50%, 94.77%, and 94.83% for 32°, 45°, 15°, 72°, and 61°, respectively. Additionally, at an inlet velocity of 2 m/s and a radial angle of 72°, 61°, 15°, 45°, and 32°, the corresponding cut-off sizes were determined to be 1.17 μm, 1.19 μm, 1.25 μm, 1.33 μm, and 1.38 μm, respectively. At an inlet velocity of 6 m/s, the peak tangential velocities were found to be approximately 1.48, 1.44, 1.44, 1.39, and 1.34 times the inlet velocity for the 15°, 72°, 61°, 45°, and 32° radial angles, respectively, within the axial location range of z = 1.5D to z = 3.4D. The peak axial velocity values for the 32°, 72°, 45°, 15°, and 61° radial angles, were reported as 0.85, 0.89, 0.92, 0.94, and 0.96 times the inlet velocity respectively.

Migration and heat transfer modeling of a neutrally buoyant melting particle in Poiseuille flow

A computational model is developed to simulate the hydrodynamic and heat transfer behavior of a melting cylindrical solid particle in plane Poiseuille flow between horizontal parallel plates. The two-dimensional transient conservation equations for mass, momentum, and energy are solved using a finite-volume scheme implemented on a deforming mesh, accounting for the rotation and non-uniform melting of the particle. An arbitrary Lagrangian–Eulerian (ALE) method is employed to directly track the moving and deforming solid–liquid interface during the particle migration and phase change. The developed model was validated by comparison with the previously reported numerical results for migration of a non-melting neutrally buoyant cylindrical particle in plane Poiseuille flow with heat transfer. The effects of flow Reynolds (Re), Grashof (Gr), and Stefan (Ste) numbers, as well as the initial position of the melting particle across the channel on the particle trajectory, melting rate, and average Nusselt (Nu) number were investigated. It was found that the melting rate increased by increasing Gr and Ste and decreased by increasing Re. The Nu did not change more than 20% with increasing Re number from 100 to 1000, but increased significantly by increasing Gr. It was also observed that by increasing Re, the particle migrates toward the channel center because of the stronger Magnus effect. Increasing Gr, on the other hand, pushes the particle to the bottom wall due to the stronger downward flow adjacent to the particle induced by buoyancy-driven convection (natural convection).

Slurry flow characteristics through a horizontal pipeline at different Prandtl number

The settling behavior of solid particles in the slurry pipeline leads to bed formation and sedimentation at the bottom of the pipeline. This in turn causes the blockage of the pipeline resulting in more energy consumption and a pressure drop in the slurry pipeline. The present work investigates the effect of the different Prandtl numbers on the slurry flow characteristics through a horizontal pipe. Since the flow is a liquid-solid mixture, therefore, a steady-state three-dimensional Eulerian two-phase model in combination with the RNG k-ε turbulence model is implemented for the current simulation in the commercial software ANSYS FLUENT. Numerical predictions and procedures for the mixture of solid concentrations are generally in good agreement with the past experimental data available in the literature. Slurry flow features are examined at four different Prandtl numbers i.e., 2.88, 3.42, 4.62 and 5.83 for different-sized glass beads (125, 200, 275, 350 and 440 μm) slurry for the concentration ranging from 40 to 60% (by weight) at a mean flow-velocity of 5 m/s. The findings show that the pressure drop rises with the escalation in particle sizes and Prandtl number for chosen efflux concentration range. Furthermore, low Prandtl fluid demonstrates relatively higher granular pressure, temperature and wall shear stress, which further increases with raise in solid concentration and particle size. In addition, higher Prandtl number fluid demonstrates maximum specific energy consumption (SEC) for every particle and efflux concentration range. • 3D CFD modeling of slurry flow via horizontal straight pipe is investigated. • Effect of different Prandtl number on slurry flow characteristics is studied. • Effect of particle size and concentration on slurry pressure drop is presented. • At lower Prandtl number, maximum granular pressure and temperature is established. • Transportation of slurry with higher Prandtl fluid is more energy efficient.

Analysis of Dynamic Behavior of Gas Bubbles and Solid Particles in an Oscillatory Baffled Reactor and Its Application to Design of Hydrogenation Proces

Analysis of Dynamic Behavior of Gas Bubbles and Solid Particles in an Oscillatory Baffled Reactor and Its Application to Design of Hydrogenation Proces

Studying the effect of shear induced lift on the transport behavior of solid particles in an inclined channel using 2D segregation-dispersion model

In this study, a 2D segregation-dispersion model has been used to study the effect of shear induced lift on elutriation within a Reflux Classifier under continuous process conditions. The Reflux Classifier is a beneficiating technology comprising a fluidized bed with a set of parallel inclined channels above it. A 2D segregation-dispersion model of the device was utilized to study the mechanism of shear induced lift introduced as a contribution to the dispersion in the x-direction within the inclined channel. A multi-solid feed, 42 types of particle species having different densities and sizes, was simulated. It was observed that due to the shear induced lift, a phenomenon of particle resuspension occurred causing relatively higher solid volume fractions in the middle zone of the inclined channel. This happened because the coarse low-density particles experienced a higher shear induced lift and their concentration increased toward the middle zone. These coarse low-density particles and fine low-density particles moved out from the system via the overflow. Whereas, the fine dense particles experienced a low shear induced lift, hence, settled, slide backward, and discharged in the underflow. The lower Ep values ranging from 0.03 to 0.05 were obtained showing an improved separation performance.

Simulation of the solid particles behavior in 3D stirred tank using CFD-DEM coupling approach

The computational fluid dynamics-discrete element coupling method is used to simulate the suspension behavior of solid particles in a stirred tank, and the motion trajectories and collision motions of millions of particles are analyzed. These particles have complex interactions with the liquid and the rotating impeller. In this article, we introduce a slip grid method, which is an important method to realize the CFD-DEM coupling. We discuss the influence of liquid flow on the trajectory of solid particles, and analyze the relationship between the eight physical properties of solid particles. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.

Investigation of single particle devolatilization in fluidized bed reactors by X-ray imaging techniques

A non-intrusive X-ray imaging technique has been used to investigate the behaviour of solid feedstock particles in a lab-scale fluidized bed reactor operated at temperatures up to 650 °C. Beech wood and polypropylene particles of different sizes have been chosen to represent the main constituents of typical thermochemical processes feedstock. The experiments were conducted under either oxidizing or inert conditions. The presence of oxygen showed a strong effect on the overall devolatilization time, which was found to be in the range of 30–112 s and 40–174 s for beech wood and polypropylene, respectively. Surprisingly, the oxidizing nature of the fluidizing medium appears to have no influence on the volatiles release within the bed in form of the so-called endogenous bubbles. These volatiles bubbles are responsible for a lift force acting on the feedstock particle itself, which ultimately encourages the segregation towards the bed surface. A one-dimensional physical model has been developed to predict particle axial location over time, taking into account both dynamic and thermal conversion behaviour of a single feedstock particle. A revised version of the model has been proposed due to new knowledge of endogenous bubbles size provided by a novel X-ray imaging approach. Results showed very accurate predictions of the 1D model for biomass particles, which segregate towards the bed surface according to the multiple bubble segregation pattern. However, the model fails in describing plastics behaviour, possibly due to different mechanisms of reactions. The observations reported in this work show the importance of investigation at single particle level and may serve to promote new methods to gain a better understanding of plastics thermal decomposition in fluidized beds, whose mechanism is still uncertain.

Analysis of Complex Solid-Gas Flow under the Influence of Gravity through Inclined Channel and Comparison with Real-Time Dual-Sensor System

Gas-solid flow is used in the chemical industry, food industry, pharmaceuticals, vehicles, and power generation. The calculation of flow has aroused great interest in contemporary industry. In recent decades, researchers have been seeking to build an effective system to monitor and calculate gas-solid flow. Attempts have been extended from computational modeling to the creation of flow pattern visualization methods and mass flow (MFR) quantification. MFR is usually studied by volume flow concentration (VFC) and velocity distribution of solid particles. A non-invasive device is used for testing MFR, in which electronic and mechanical sensors are used to balance the shortcomings related to each other. This study investigates the simulation of flow patterns to demonstrate the behavior of solid particles as they pass through the channel. The particles are allowed to slide longitudinally in the insulated tending channel. This slippage is due to the influence of natural gravity. Electronic sensor components are used to measure the velocity distribution and concentration of volumetric flow. The load cell is used as an auxiliary sensor for measuring MFR. In addition, ANSYS fluent is used to analyze streaming queries. The experimental results are related to evaluating the accuracy and relative error of the data collected from various sensors under different conditions. However, the simulation results can help explain the movement of the gas-solid mixture and can understand the cause of pipeline blockage during the slow movement of solid particles.

Experimental research of liquid droplets colliding with solid particles in a gaseous medium

This article presents the research findings on binary collisions of water droplets and solid particles using three most widely spread ranks of coal. The experimental setup used in this research allowed the variation of the particle size from 0.25 mm to 0.75 mm and the velocity from 0.5 m/s to 4 m/s. The droplet velocity was varied from 0.3 m/s to 6 m/s. The impact angle of attack ranged 0–90°. These variation ranges of initial parameters correspond to promising gas–vapor–droplet technologies such as spray drying, fire extinguishing, water treatment, fuel mixing and combustion, heat and mass transfer power plants, etc. We analyzed the frames showing three collision regimes: coalescence, separation, and disruption. We determined how the temperature of the liquid medium affects the position of droplet collision regime boundaries on the corresponding maps in the B(We) coordinates. We also determined the impact of hydrophilic and hydrophobic behavior of solid particles on the collision characteristics. The size distributions were established for secondary fragments formed during the collision of water droplet and solid particle, as well as the collision of two droplets. The key patterns of the processes under study were singled out for various droplet shapes and size ratios. Finally, we compared the characteristics and conditions of interaction between water droplets and water-based slurries.

Numerical investigation on deposition rate of mechanically mixed ash particles in an entrained flow reactor

AbstractHomogeneous nucleation and heterogeneous condensation of salt vapors near the wall of superheater or reheater tubes greatly improve the sticky propensity of deposited surfaces or impacting particles and then lead to a fast‐growing rate of initial layer. Based on the deposition experiment of mechanically mixed KCl + SiO2 particles in an entrained flow reactor, a numerical model with considering the salt particle vaporization, salt vapor condensation, and its effect on SiO2 deposition is proposed for simulating impaction and adhesion behavior of molten and solid particles. The results show that deposits are mainly from the impaction of solid and molten particles and the condensation of salt vapors. The condensation rate of salt vapors in the stagnation zone at the windward side of metal probe is maximal. In comparison with the overall deposition rate, although the amount of salt vapors condensed on the probe surface can be negligible, it significantly affects the deposition rate of SiO2 particles. The coupled CFD model over a link between particle sticking and salt vapor condensation could well simulate the deposition behavior of mechanically mixed ash particles under rich‐salt‐vapor atmosphere.

Coarsening of solidβ-Sn particles in liquid Pb-Sn alloys: Reinterpretation of experimental data in the framework of trans-interface-diffusion-controlled coarsening

Previously published data, not ours, on the coarsening of solid \ensuremath{\beta}-Sn particles in a liquid Pb-Sn matrix of near-eutectic composition are reanalyzed within the framework of the trans-interface-diffusion-controlled (TIDC) theory of coarsening. The data were obtained under conditions of microgravity from specimens heat-treated at 458 K and containing four equilibrium volume fractions ${f}_{e}$ equaling 0.10, 0.15, 0.20, and 0.30. We show that the rate constants $k({f}_{e})$ in the traditional coarsening equation ${\ensuremath{\langle}r\ensuremath{\rangle}}^{3}\ensuremath{\approx}k({f}_{e})t$ for the kinetics of growth of the average particle radius $\ensuremath{\langle}r\ensuremath{\rangle}$ are nearly independent of ${f}_{e}$, in disagreement with numerous theories wherein coarsening is controlled by diffusion in the host matrix phase. Atom transport in TIDC coarsening is instead controlled by slow diffusion through the diffuse interface, of width \ensuremath{\delta}, separating the dispersed particles from the matrix; the kinetics of this process is independent of ${f}_{e}$. Atomistic simulations were performed to estimate the properties of the solid-liquid (S-L) interface at 458 K, 2 K above the Pb-Sn eutectic temperature. The S-L interfaces normal to (001) and (010) of tetragonal \ensuremath{\beta}-Sn were examined and found to have nearly identical properties, including interface widths of \ensuremath{\sim}1.7 nm. In conjunction with the diffusivities in solid \ensuremath{\beta}-Sn and liquid hypereutectic Pb-Sn at 458 K, we estimate that TIDC coarsening should prevail for solid Sn particles \ensuremath{\sim}1700 \ensuremath{\mu}m in radius, far exceeding the maximum radius of \ensuremath{\sim}100 \ensuremath{\mu}m measured experimentally. The TIDC theory also predicts that the kinetics of growth obeys the equation ${\ensuremath{\langle}r\ensuremath{\rangle}}^{n}\ensuremath{\propto}t$. The temporal exponent $n$ was evaluated to be \ensuremath{\sim}2.5, as ascertained by analyzing data on the particle size distributions (PSDs; histograms) for the alloys with ${f}_{e}=0.15$, 0.20, and 0.30. The histograms were converted to experimental cumulative distribution functions (ECDFs) and analyzed using the Kolmogorov-Smirnov (K-S) test applied to the theoretical CDFs predicted by the TIDC theory. We report the first successful application of the K-S test to experimental PSDs concomitant with particle coarsening. From every aspect of the experimental data amenable to analysis, we conclude that the coarsening behavior of solid Sn particles in liquid hypereutectic Pb-Sn alloys is fully consistent with the predictions of the TIDC theory of coarsening.

Experimental study on defluidization behaviours and its influence factors during gas switching fluidization

In this work, an investigation on the fluidization behaviour of solid particles was carried out while the fluidizing agent was switched from one gas to another with an equal volumetric flow. Four different gases, namely helium, nitrogen, argon and carbon dioxide (He, N2, Ar and CO2), were adopted as fluidizing agents, and fluid catalytic cracking (FCC) was used as the experimental material. When changing the gas supply a sharp decrease of the bed pressure drop and significant compression of the emulsion phase are observed, as well as the disappearing of the bubbles and the formation of channels inside the bed. However, these disturbances are temporary, and the initial fluidization conditions can be restored after a certain amount of time. Such behaviour is quantitatively described by measuring the maximum relative decrease of bed pressure drop, the time duration and the intensity of the defluidization phase. The effects of the initial powder bed height, the switching gas velocity and the gas properties are analyzed as well. Finally, a semi-empirical model was developed to predict the defluidization time based on the understanding of this physical process and analyzing the experimental data.