Fluidization Behavior Of Particles Research Articles

The fluidization behavior of particles in supercritical water fluidized bed: A region-dependent analysis

The distribution and fluctuation of particle concentration in a supercritical water fluidized bed (SCWFB) are studied using a specially-designed capacitance probe measurement system. The measurement error of capacitance probe system is 2.48%. Results show that the particle concentration at the axial line fluctuates largely with time and the fluctuation is weakened when increasing the distance from axial line or decreasing particle diameter. At Uf/Umb=1.5, the largest difference between particle concentrations is 0.026, 0.04, 0.082 when the particles with a diameter of 0.124 mm, 0.198 mm, 0.235 mm are used, indicating a larger non-uniformity of larger particles. The probability density of local particle concentration mainly follows a unimodal distribution with the peak at right side. The main frequency of SCWFB ranges from 1.39 Hz to 2.73 Hz in this experiment and the main frequency decreases when larger particles are used.

Multi-scale experimental investigation on the fluidization of Geldart B 13X zeolite particles: A comprehensive dataset for CFD validation

The fluidization of zeolite 13X in a bubbling fluidized bed was experimentally investigated. The objective is to analyze the fluidization behavior of particles in a lab-scale system with a total of 1.5 million particles, enabling accurate characterization of uncertainties. Validation datasets were generated for the fluidization process in a bench-scale rectangular unit. A comprehensive characterization of the particle properties, including size, density, coefficient of friction, coefficient of restitution, and minimum fluidization velocity, is presented using advanced diagnostic tools. Corresponding fluidized bed measurements, such as pressure drop and bed expansion, are reported under three test settings with different flow rates. The tested particles have a Sauter mean diameter of 1,345 μm and a density of 2,054 kg/m3. It is classified in Geldart group B for its vigorous bubbling and good mixing behavior. With increasing the superficial inlet velocity from 0.347 to 0.740 m/s corresponding to 1.41–3.01 Umf, where Umf = 0.2458 m/s is the minimum fluidization velocity, the particles tend to transit from bubbling flow to slug/plug flow regimes. Using high-speed imaging, bubble sizes and velocities in the pseudo-two-dimensional (2D) fluidized bed could be obtained directly. The data acquisition rate is 1200 fps, far above the quantities of interest (QoI) dominant frequency (typically below 10 Hz). The QoI obtained from this study were statistics of interface height, differential pressure, and particle velocities using particle image velocimetry. The results confirm consistency given the use of randomization and repeat in the run order as well as multiple batches of bed material. This experimental dataset can serve as a benchmark for validating numerical models and as a blind study for the multiphase flow modeling community.

Computational analysis of the particle size effect on the pressure profiles and type of flow regimes of TiO2 microparticles in a fluidized bed

Abstract The effect of particle size on the pressure profiles and flow regimes of the bed containing TiO2 microparticles (MPs) was investigated in a fluidized bed. The fluidization behavior of particles with mean diameters, d p , of 170, 200, 225, and 300 μm at different gas velocities, U g , was investigated both experimental and computational viewpoints. A computational fluid dynamic (CFD) model was developed by the Eulerian–Eulerian approach to evaluate the sensitivity of the Syamlal–O’Brien, and Gidaspow drag models on the predicted results of the bed pressure profiles. The results showed that with increasing particle size, the amplitude of pressure fluctuations increases and the type of flow regime in the bed tended from bubbling to slugging flow regime. The error analysis showed that the use of the Gidaspow model led to more accurate results than the Syamlal–O’Brien model in predicting the bed pressure drop and pressure fluctuations in the slugging flow regime. However, the Syamlal–O’Brien model was more suitable for predicting the pressure profiles in the bubbling flow regime. The results were more suitable for the bed containing particles of 300 μm than the beds with d p ≤ 225 μm. The highest and lowest deviations between the experimental data and simulation outputs were obtained at U g of 0.295 and 0.650 m/s, respectively. The findings confirmed that the mutual effects existed between the d p pressure profiles, and the type of flow regimes in the bed.

Thermal energy storage in fluidized bed using microencapsulated phase change materials

Fluidized beds are widely used in effective heat and mass transfer applications for chemical processes. The beds can also used for storing thermal energy (TES) and offer a rapid and effective way to exploit solar energy especially for heating applications. Microencapsulated PCMs serve as the TES medium and the fluid phase in these applications. There exist few experimental studies that have investigated uses of fluidized beds for thermal storage. The works show that properties of microencapsulated PCMs have to be fine-tuned for them to become effective in fluidized beds. This paper investigates the performance of an experimental air-fluidized bed using microencapsulated PCM as the thermal storage system for two different storage temperatures of 55 °C and 65 °C. The results show that TES using microencapsulated PCM with mean particle size of 100 μm that corresponds to A-type particle according to Geldart chart showing fluidization behavior of particles is possible. The fluidization process did not change the morphology of the microencapsulated PCM. Fast storage and recovery can easily be accomplished at efficiencies as high as 80%.

Experimental fluid dynamics of particles in a dielectric barrier discharge plasma-enhanced spouted bed

This study proposed the fluidized particles with dielectric barrier discharge (DBD) plasma in a slot-rectangular divergent-base spouted bed and focused on the dynamics of solid particles with the plasma irradiation. Two bed materials (Polypropylene (PP) particles and Polyamide (PA) particles) with same diameter (3 mm) were fluidized in this study. Fluidization parameters included gas velocity (7.4–14.9 m/s), particle amount (100–500), and plasma parameter (apply voltage, 0 and 7 kV) as the applied voltage were investigated here. Particle velocity profiles were analyzed through the methods of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Results show that the particle velocity was increased with the plasma irradiation, mainly by the enhancement in the vertical direction. The location of the highest particle velocity area related to the fluidization behavior of particles. With the increase of superficial gas velocity, the location of the highest particle velocity area raised along the central line but not reached the top of the solid bed. While the electron temperature of Ar plasma decreased with the addition of particles. Two electric fields (external electric field and surface charge electric field) presenting in the system were assumed to give the reason for the changes of the particle fluid dynamics.

On the numerical implementation of the Van der Waals force in Soft-Sphere Discrete Element Models for gas-solid fluidization

Attractive inter-particle forces, such as Van Der Waals forces (vdw), are known to strongly influence the fluidization behavior of particles classified as Geldart C-type, and recent literature suggests that vdw forces may also become important for Geldart A and B type particles at elevated temperatures. Discrete Element Models (DEM) using a soft-sphere collision model have been developed to investigate the effects of particle–particle and particle-gas interactions on the fluidization behavior in great detail. However, it is shown that inconsistent results may be obtained with soft-sphere based DEM, depending on the numerical implementation of the vdw forces, particularly related to the calculation of the vdw forces for overlapping particles during particle collisions, as is usually done in the literature. In this work we present a new numerical approach that allows the calculation of the vdw force for particles that are in contact in a physically sound way, corresponding with theoretical arguments given by Rietema et al. (1993). We also provide a generic protocol to determine the relevant parameters based on our new approach, which will allow future work to simulate gas-solid fluidized beds with attractive inter-particle forces in a soft-sphere DEM framework.

Development of suitable product recovery systems of continuous hybrid jig for plastic-plastic separation

A modified jig called the hybrid jig was recently developed to separate mixed-plastics with similar specific gravities effectively using the concepts of bubble attachment, surface wettability and gravity separation. This method was effective in a batch-type jig setup, but when applied to a continuous-type jig setup, the efficiency of the process dramatically decreased. This drop in efficiency was attributed to the unintended negative effects of air bubbles on separation especially close to the screw-type extractor at the product end though this type of product recovery system was successfully applied to the RETAC and reverse jigs. To address this problem, a better product recovery system for continuous-type hybrid jig is proposed in this study, and the effects of air injection rate at different positions of the hybrid jig separation chamber were evaluated. The results showed that fluidization behavior of particles in the hybrid jig was influenced by not only water pulsation but also the rising motion of air bubbles. To improve the purity of heavy materials in the bottom layer products, two product recovery systems are proposed: (1) a screw-type extractor with one “separating” single-screen, and (2) a screw-type extractor with modified air injection and water pulsation (i.e., upward flow period was shortened).

Optical emission spectroscopy diagnostics of DBD plasma with particles in a two-dimensional spouted bed

To gain an insight into the effect of fluidization behavior of particles on the characteristic of plasma in a plasma-enhanced spouted bed, we investigated the changes of plasma optical emission spectroscopy (OES) with fluidized particles in this paper. Fluidization experiments under the irradiation of a dielectric barrier discharge (DBD) plasma generator were performed in a two-dimensional spouted bed. Essential operation parameters, such as particle type, applied voltage, gas velocity, and particle number were changed. The pressure drop of particles, emission intensity (EI) of plasma, and high-speed camera images of plasma pattern were measured. As the results, the fluidization behavior of particles had been changed by the plasma irradiation, especially for polypropylene (PP) particles. The emission spectra of argon (Ar) plasma had been changed significantly with particles. The emission intensities of the Ar I transition lines were increased, and Ar II lines were decreased with PP particles compared to the case of no particle. The emission intensity of Ar I lines was enhanced with the applied voltage regardless of the addition of particles. The emission intensity changed with a gas velocity versus particle numbers was identified with the fluidization behavior, that emission intensity was increased at first and then decreased. The gas velocities corresponded to the highest value of emission intensity with various particle number were similar to the trend of the changes of minimum spouted velocity. The electrical conductivity and color of particles may affect the difference of pressure drop and detected emission intensity for two kinds of particles. Our research extends the knowledge of the relationship between fluidization behavior and plasma optical characteristic.

Reactor concepts for atomic layer deposition on agitated particles: A review

The number of possible applications for nanoparticles has strongly increased in the last decade. For many applications, nanoparticles with different surface and bulk properties are necessary. A popular surface modification technique is coating the particle surface with a nanometer thick layer. Atomic layer deposition (ALD) is known as a reliable method for depositing ultrathin and conformal coatings. In this article, agitation or fluidization of the particles is necessary for performing ALD on (nano)particles. The principles of gas fluidization of particles will be outlined, and a classification of the gas fluidization behavior of particles based on their size and density will be given. Following different reactor concepts that have been designed to conformally coat (nano)particles with ALD will be described, and a concise overview will be presented of the work that has been performed with each of them ending with a concept reactor for performing spatial ALD on fluidized particles.

The effect of vibration on bed voidage behaviors in fluidized beds with large particles

The effects of vibration parameters, operating conditions and material properties on bed voidage were investigated using an optical fiber probe approach in a vibrating fluidized bed with a diameter of 148 mm. Variables studied included frequency (0-282 s-1), amplitude (0 mm-1 mm), bed height (0.1 m-0.4 m) as well as four kinds of particles (belonging to Geldart's B and D groups). The axial and radial voidage distribution with vibration is compared with that without vibration, which shows vibration can aid in the fluidization behaviors of particles. For a larger vibration amplitude, the vibration seriously affects bed voidage. The vibration energy can damp out for particle layers with increasing the bed height. According to analysis of experimental data, an empirical correlation for predicting bed voidage, giving good agreement with the experimental data and a deviation within ±15%, was proposed.

Effect of Fluid Viscosity on Liquid−Solid Fluidization

Four kinds of solid particles were fluidized and tested in aqueous solutions of glycerol ranging in viscosity from 7 to 1400 cP. Two trends in which the fluidization behavior of particles is significantly affected by fluid viscosity were observed, and a physical model was proposed based on these phenomena. On the one hand, increasing the fluid viscosity could decrease the bubble size, which results in smoother fluidization. On the other hand, because of the effect of the laminar layer, particle agglomeration could occur when the fluid viscosity is high enough, which results in heterogeneous behavior in the fluidized bed. At the critical point, these two trends balance each other, and the best fluid quality is observed. For all particles in this work, although the values of optimal viscosity are different, the values of the particle terminal Reynolds number are about 0.004 at the critical point.

A new criterion for prejudging the fluidization behavior of powders

A new intrinsic criterion, equivalent specific surface area S ̂ e , is proposed, by which different fluidized behaviors of particles can be classified. In addition, this criterion has been introduced to prejudge fluidization behaviors of mono-component particles which have wide size distributions and multi-component mixtures of Geldart's type A, B or D powders.

Fluidization behavior of particles under agglomerating conditions

To obtain fundamental information on the fluidization behavior of sticky particles, a visually observable fluidized bed, which can be operated under conditions in which agglomeration of the bed materials occurs, was designed and constructed. Polyethylene particles and silica sand coated with a thin layer of low melting point polymer were chosen as bed materials. Two types of fluidizing gas distributors were used: a porous plate and a porous plate with an independently fed jet at the center. Our fluidized bed was operated in continuous-feed mode and in batch mode. The weight percentage of the aggomerates was measured at different residence times, jet air velocities, and jet and auxiliary air temperatures, using different particle sizes, coating thicknesses, and concentrations of coated particles in the fluidized bed. In the case of polyethylene particles as bed material in the batch system, the amount of agglomerates generated increased linearly with residence time and increased exponentially with either auxiliary air or jet air temperatures. Within the operating conditions of our study, the amount of agglomerates generated increased with jet nozzle size at the constant jet air flow rate. Under conditions of high temperature, a low jet velocity resulted in excessive agglomeration, which led to catastrophic sintering and defluidization. In the case of coated particles as bed materials in our batch fluidized bed, the amount of agglomerates generated increased with residence time and then leveled off. It increased sharply with jet air temperature, coating thickness, concentration of coated particles and decreasing particle sizes in the range of our experimental conditions.