Fluidized State Research Articles

Dissipation behaviors in submerged beam-vibrated granular systems

This study investigates intruder dynamics within granular systems, focusing on energy dissipation and phase transitions influenced by beam vibrations. Using a granular-beam experimental setup and discrete element method (DEM) simulations, we explore the dynamic responses of a simply supported beam in a granular medium under various excitation conditions. Our results reveal distinct granular phase states and their evolution pathways, driven by changes in excitation amplitude and frequency, which significantly affect energy dissipation. Key findings include the identification of vortical and disordered fluidization states that correlate with extremes in energy dissipation, underscoring the importance of characteristic lengths and times in characterizing these transitions. Additionally, amplitude-frequency characteristics and mean squared displacement (MSD) analyses link microscale particle behavior with macroscale beam dynamics, providing insights into the mechanisms of energy dissipation and dynamic heterogeneity. This research enhances our understanding of granular system mechanics, offering implications for the design and optimization of engineering applications across various fields.

Development of explainable recognition models for ADMFB flow regimes based on ensemble learning

The spatiotemporal characteristics of fluidization within an Air Dense Medium Fluidized Bed (ADMFB) are critical for its heat and mass transfer, as well as for mixing and separation processes. Yet, detailed analyses of the dynamic behavior of flow regimes during progressive transformations are scarce. This study captured synchronous pressure drop signals at multiple points along the sidewall of the bed using a non-intrusive measurement technique. Statistical analyses were utilized to extract the pressure drop's characteristic parameters and examine the statistical features' spatiotemporal fluctuations during fluidization state transitions. We proposed a method to quantitatively characterize the bed's real-time fluidization state through the combined use of multiple-point pressure characteristics. Following this approach, a multidimensional spatio-temporal matrix was constructed to depict the flow regime transitions quantitatively. Concurrently, ensemble learning techniques were applied to classify flow regimes based on various feature parameters and sample lengths. In the final phase, comprehensive interpretations and detailed visual analyses were deployed on the inputs to the optimized ensemble learning model, XGBoost, utilizing the Shapley Additive Explanations (SHAP) framework. This study provides additional insights and methodologies for managing the transition and intelligent control of flow regimes within an ADMFB.

Flow Behavior of Nanoparticle Agglomerates in a Fluidized Bed Simulated with Porous-Structure-Based Drag Laws.

Fluidization bed reactor is an attractive method to synthesize and process quantities of functional nanoparticles, due to the large gas-solid contact area and its potential scalability. Nanoparticles fluidize not individually but as a form of porous agglomerates with a typical porosity above 90%. The porous structure has a significant effect on the hydrodynamic behavior of a single nanoparticle agglomerate, but its influence on the flow behavior of nanoparticle agglomerates in a fluidized bed is currently unclear. In the present study, a drag model was developed to consider the porous structure effects of nanoparticle agglomerates by incorporating porous-structure-based drag laws in the Eulerian-Eulerian two-fluid model. Numerical simulations were performed from particulate to bubbling fluidization state to evaluate the applicability of porous-structure-based drag laws. Results obtained for the minimum fluidization and bubbling velocities, bed expansion ratio, and agglomerate dispersion coefficient show that, compared with the drag law of solid sphere, the porous-structure-based drag laws, especially the drag law of fractal porous spheres, provide a closer fit to the experimental data. This indicates that the pore structures have a great impact on gas-solid flow behavior of nanoparticle agglomerates, and the porous-structure-based drag laws are more suitable for describing flows in nanoparticle agglomerate fluidized beds.

Cohesive behavior of CaO-based particles in fluidization during CaO/CaCO3 heat storage process: Experiments and molecular dynamics simulations

CaO/CaCO3 heat storage is considered a promising technology to solve the intermittency of solar energy. Fluidized-bed reactor is commonly used as calciner/carbonator to efficiently achieve heat storage. In the fluidized-bed reactor, the particle cohesion impedes fluidization of CaO/CaCO3 particles, adversely impacting heat storage. However, the current research rarely focuses on the cohesive behavior of CaO-based particles in fluidization during CaO/CaCO3 heat storage process. Furthermore, current research on cohesive behavior primarily focuses on experimental studies, lacking an explanation of the underlying mechanisms at the molecular level. In this work, the cohesive behavior of CaO-based particles in CaO/CaCO3 heat storage process was studied on a fluidized-bed reactor. The particle cohesion is reflected by the tensile yield strength during the transition from static state to fluidization state. The results indicate that the cohesive behavior of CaCO3 particles gradually is strengthened with increasing temperature. The tensile yield strength of CaCO3 particles at 800 °C is 1770 Pa, which is 200 % higher than that at 500 °C. Additionally, the carbonation enhances the cohesive behavior of CaO particles. The tensile yield strength of CaO particles after the carbonation is 55 % higher than that of before the carbonation. The enhanced cohesive behavior of CaO particles during the carbonation results in the defluidization. Molecular dynamics simulation shows that the formation of sintering necks at above 650 °C in the carbonation stage results in cohesive behavior of CaO particles. The introduction of 5 % Al2O3 fines (50–75 μm) as lubricant effectively improves the fluidization quality of CaO particles in the carbonation stage, thereby enhancing the exothermic performance of CaO particles. These findings provide valuable insights for the industrial application of CaO/CaCO3 heat storage in fluidization.

Fluid Dynamics Investigation in a Cold Flow Model of Internal Recycle Quadruple Fluidized Bed Coal Pyrolyzer

Internal recycle quadruple fluidized bed pyrolyzer (IR-QFBP) consists of a dual fluidized bed pyrolyzer and a dual fluidized bed combustor and is proposed in this work. It is a new kind of efficient fluidized bed with high pyrolysis and energy efficiency. IR-QFBP may attract extensive attention because of its compact structure. Cold hydrodynamic characteristics of IR-QFBP are the bases of modeling and designing for the hot one. To fully understand the hydrodynamic characteristics of IR-QFBP, a cold flow model on a laboratory scale was designed and set up; furthermore, the two-fluid model (TFM) based simulation was also carried out. The pressure profiles, fluidization states, velocity profiles, and circulation rates of a solid powder at different operation conditions in IR-QFBP were investigated. The results showed that the stable internal circulation of solid powder can be achieved in IR-QFBP. And different circulation characteristics can be obtained by adjusting the operating conditions.

Introducing an efficient capped fluidized bed and quantifying its flow and heat transfer performance

Fluid-solid particle beds have a very wide range of industrial applications but there are few publications relating to a general method to quantify solid particle bed performance for a comparative efficiency study. The conventional approach of characterizing bed efficiency involves bubble sizes, bubble frequency, byproduct quantity for bed reactors, and pressure drop for minimum fluidization. However, different solid particle beds have different states with varying flow rates, which makes the comparative study more difficult to achieve. In this work, a common approach to measure solid particle bed efficiency in terms of heat transfer is presented. The two cases considered here are 1) When work is done by the particles such as in a catalytic reactor, and 2) When work is done on the particles such as in cooling/drying of particles. In addition to the packed bed and fluidized bed, a solid particle bed called a capped fluidized bed is introduced. The Eulerian–Lagrangian method, also known as CFD-DEM simulation, is adopted for this analysis. Numerical simulations show potentially significant advantages of capped beds over packed and fluidized beds under certain fluidization states. Capped fluidized bed pressure drop is comparatively lower than that for a packed bed and similar to a fluidized bed, which allows it to operate at a wider range of flow states. Current fluidized bed performance is limited by the entrainment and possible loss of particles at high flow rates. However, the capped fluidized bed restricts the particles from leaving the bed and thus permits higher flow rate operation. Further experimental research is required to more completely characterize this type of solid particle bed.

Simulation of Heat and Mass Transfer in a Moving Bed Part-Fluidized Boiler

Abstract Moving bed part-fluidized boiler is a new type of furnace. The new combustion method in the furnace has attracted a lot of attention and shown attractive prospects. Two-dimensional computational fluid dynamic (CFD) simulations were performed for a 116 MW moving bed part-fluidized boiler to investigate the different combustion patterns of coal particles of different particle sizes inside the furnace chamber. A low-NOX combustion method based on the combination of laminar combustion and fluidized combustion is proposed. By comparing the effects of different air distributions on the fluidization state of coal particles, the air distribution values required for optimal fluidized combustion were obtained. The temperature field and pollutant distribution in the furnace chamber for the conventional combustion method and the new combustion method were also simulated. The results show that the combustion technology combining laminar combustion and fluidization of a moving bed part-fluidized boiler can significantly improve the combustion rate and reduce the NOX concentration at the furnace exit. When the secondary air speed is up to 15 m/s, the coal particles smaller than 5 mm are fully fluidized and burned in the whole furnace chamber. The coal particles larger than 5 mm are burned on the bed. The pollutant emission of the boiler can reach the best condition. The new type of boiler can reach a super clean emission in which the NOX emission value is below 47 mg/m3, and the SO2 emission value is reduced to 0.15 mg/m3.

Implementation of Fluidized Bed Concept to Improve Heat Transfer in Ecological Adsorption Cooling and Desalination Systems

Sustainable development policy focuses on reducing the carbon footprint generated by the global industry and energy sector. Replacing conventional energy sources with environmentally friendly ones requires advanced research to increase energy efficiency and reduce the instability and intermittence of renewable sources. Moreover, adsorption chillers are an opportunity to introduce net-zero emission technologies to the refrigeration, air-conditioning, and desalination industries. Adsorption devices could be popularized if a method of effective heat transfer in the volume of the adsorption bed is developed. The innovative concept of introducing fluidized beds into the adsorption system can achieve the most promising results in improving energy efficiency. To confirm the adopted assumption, heat transfer coefficient calculations for the packed and fluidized bed were carried out in this paper based on experimental tests and literature data. The empirical research aims to extend the fundamental knowledge in the implementation of fluidization under low-pressure conditions, characteristic of the adsorption systems’ working cycle. Experiments were conducted on a unique test stand equipped with the Intensified Heat Transfer Adsorption Bed (IHTAB) reactor prototype. Five adsorption bed samples were analyzed. The reference sample consisted only of silica gel, and the subsequent ones contained aluminum or carbon nanotubes with 5 and 10% additions. In the case of samples with admixtures, the fluidized state increased the heat transfer coefficient on average from approx. 36.9 W/m2 K to approx. 245.4 W/m2 K.

Fluidization characteristics of wide-size-distribution particles in the fluidized bed with heating plate

To study the effect of heating plate on fluidization characteristics, the mean bed voidage, the axial solid concentration and pressure fluctuation under different superficial gas velocity were investigated. Experiments were conducted in a fluidized bed of 1500mm in height and 215 mm internal diameter with a conic bed. The results show that the internal heating fluidized bed has a little higher pressure drop, a little lower bed voidage, but a more stable fluidized state. The increase of the coalescence and breakage frequency of the bubbles can explain that the heating plate breaks the big bubbles well.

A numerical study of fluidization characteristics in transition from aggregative to particulate flow

A comparative study on the fluidization characteristics from aggregative to particulate fluidization with increasing fluid density and viscosity is carried out using the two-fluid models (TFM), to study the vast transitional states in between. Two representative transitional fluidization states are observed as the fluidized state changes progressively from aggregative to particulate fluidization. As the discrimination number (Dn) adopted to delineate the transition decreases, the increasing number of local vortexes promotes more internal particle circulation, and a reduction in the bubble phase and the dense phase fractions but an increase in solids holdup in the intermediate phase. As a result, the intermediate phase become more interconnected and solids movement are enhanced. The interaction between the solids and the fluid phases is also increased and the intensity of particle-particle interaction is decreased with decreasing Dn. Fluid density has more significant effect on the above changes than fluid viscosity.

Gas fluidization of natural graphite flakes

Demand for high purity graphite is expected to greatly increase in the coming decades. Mined graphite is purified to the final purity specification via thermal and/or chemical fluid-solid processes. As fluidized bed electro-thermal purification is a promising technology, the physical characterization and cold-flow fluidization of Canadian natural flake graphite was undertaken to better understand the gas-solid dynamics. Three commercial graphite particle batches were characterized. Mean Sauter diameters of the three particle populations measured by microscopy were 89, 63 and 51 μm. The modified sieve analysis and permeametry yielded similar mean diameters. Particle sphericities were determined to be 0.34, 0.36 and 0.40 respectively. Channelling near the surface occurred near minimum fluidization (vmf) but eventually disappeared with increasing gas velocity. This led to a partial fluidization state before achieving complete fluidization with the delay, which was observed to be up to around 3vmf, being greater for the smaller particles. Minimum fluidization velocity was determined to be 0.063, 0.028 and 0.011 m/s respectively. Complete fluidization was observed at velocities of approximately 0.070, 0.046 and 0.035 m/s respectively. Finally, wall effects due to the presence of a central electrode did not significantly impact overall fluidization characteristics.

Effect of fines addition on heat transfer performance in gas-solid fluidized bed: An integrated experimental, simulation, and theoretical study

Efficient heat transfer is crucial in industrial fluidized beds, especially for highly exothermic or endothermic processes. In this study, the influence of adding fines on the heat transfer performance in fluidized bed is investigated through experiments, simulations, and theoretical analysis. Experimental results from a hot/cold-wall fluidized bed show that fines addition enhances the heat transfer performance. Notably, the bed-wall heat transfer coefficient presents a volcano-shaped curve with increasing fines proportion, with a discernible threshold at ∼25 vol%. Our simulations and theoretical analysis reveal that the improved particle dispersion due to fines addition is responsible for such volcano-shaped phenomenon. Theoretical analysis based on kinetic theory further uncovers that fines addition leads to an increased difference between the solid volume fraction in fluidization state and that in packing state, creating more free-space for particle moving, thereby improving particle dispersion, and thus enhancing heat transfer in fluidized beds.

CFD-DEM Simulation of Slugging and Non-Slugging Fast Fluidization of Fine Particles in a Micro Riser

The discrete element method (DEM) coupled with computational dynamics (CFD) has been considered one of the most sensitive ways of studying the micro fluidized bed. This article proposes a so-called particle circumstance-dependent drag model that is dependent on a particle’s complex circumstances. Slugging and non-slugging fast fluidization in a micro fluidized bed is modeled with the use of the CFD-DEM. The results show that the formation and the fragmentation of clusters in a slugging fast fluidized state are clearly captured, and both have time synchronization. However, with the increase in gas velocity, the boundary of the dense and dilute phases turns blurry and the slugs disappear. Furthermore, there exists a relatively serious backmixing of particles in the slugging fast fluidization, while the backmixing effect weakens in the non-slugging fast fluidization. Moreover, the outlet solid flux decreases compared with those in the big fluidized beds for the slugging fast fluidized bed due to the micro size effect, while the micro size effect on the solid flux is not distinct for the non-slugging fast fluidized bed. Last but not least, the radial porosity with slugging exhibits a weakened core-annulus structure compared with the correlated radial porosity in the big fluidized beds. The radial porosity without slugging tends to approach the correlated core-annulus structure.

Numerical Simulation of Fluidization Behavior and Chemical Performance for Hydrochlorination of Silicon Tetrachloride in a Fluidized Bed Reactor

Exploring the fluidization behaviors and chemical performance in silicon tetrachloride (SiCl4) hydrochlorination processes within a fluidized bed reactor (FBR) poses significant challenges. In this study, we developed an Eulerian-granular model (EGM) by integrating the Eulerian–Eulerian two-fluid model with the kinetic theory of granular flow (KTGF). The effect of fluidization velocities on the flow regime, heat transfer, and chemical reaction performance were investigated. The applicability of the simulation method and the validity of the model were confirmed through comprehensive comparisons, including the simulated values of the maximum bed expansion height (Hmax) with theoretical values derived from empirical formulas and the simulated gas temperature profile with Hsu’s experimental data. The results indicate that the present EGM can be feasible to describe the variation of the flow regime within the FBR. An increase in bed voidage over time, coinciding with transitions in the flow regime, can be observed. Particularly noteworthy was the attainment of a more uniform distribution of SiCl4 under the bubbling fluidization state. Furthermore, the FBR possess high heat transfer characteristics, and the reaction gas can reach the set temperature of the bed after entering a small distance (about 10 mm). The presence of circulating bubbles within the FBR enhances the mixing uniformity of the SiCl4 reaction gas and silicon particles, particularly in the central and upper regions of the bed under the bubbling fluidization state. As a result, the predicted highest concentration of SiHCl3 was 13.08% and the conversion rate of SiCl4 was 28.97% under the bubbling fluidization state. Our results can provide a theoretical basis for further understanding of the hydrochlorination process of SiCl4 within the FBR.

Particle coating growth behaviors in a spray fluidized bed based on Gas-Liquid-Solid Quasi-Three-phase DEM numerical simulation

Wet granulation processes are widely used in chemical, food, pharmaceutical, and various other industrial processes. During the process of particle coating growth, particle fluidization state and liquid characteristics have an impact on the layer's thickness and homogeneity. In this study, discrete element, liquid bridge, and droplet motion models were combined to investigate the impact of injection gas velocity, droplet diameter and injection liquid viscosity on the particle growth ratio and coating thickness distribution, and the particle growth mechanism was investigated. The particle growth area, which is the area where the number of coated particles exceeds 0, was significantly expanded by decreasing the droplet diameter and increasing the gas velocity at appropriate ranges. The frequency of droplet and particle collisions increased, and average relative liquid content decreased with increasing particle growth area. By accelerating the injection of gas and reducing the viscosity of the injected liquid, the fluidization condition of the particles, which primarily affected the particle cycle frequency, could be enhanced. The improvement of particle growth area and particle cycle frequency allowed more particles to participate in growth and improved the quality of the grown particles. The proportion of small particles dramatically grew while the proportion of large particles reduced. The standard deviation of particle diameter decreased, and particle growth became more uniform.

Hydrodynamics of a Multisized Particle Mixture in Shallow Fluidized Bed With Immersed Tubes

Abstract Inert solid particles have made the integration of more efficient power cycles with super high operating temperatures into the concentrated solar power (CSP) station feasible. Fluidized bed heat exchangers with feature of high heat transfer coefficient have great application potential in the particle-based CSP. However, the parasitic loads of the additional fluidizing gas loop and the finely sieved monosized particles may deteriorate the economic efficiency of the integrated system. In order to cope with this problem, a conceptual design of a shallow fluidized bed (SFB) heat exchanger is proposed for the new generation CSP technology. Fluidization characteristics of bauxite particles with a nonuniform particle size distribution in SFB with immersed tubes are investigated with a combination of experimental measurements and computational fluid dynamics simulations. Results show that the static bed height and opening area ratio of the distributor has insignificant influence on the range of semifluidized region and the minimum fluidization velocity Umf. The standard deviation of bed pressure drop σ in the grid region can be used as an alternative criterion for identifying the fluidization state. A range of superficial velocity that distinguishes two different solid circulation patterns exists, with its boundary values being four times and eight times the Umf, respectively. The immersed tubes can inhibit the asymmetric particle circulation patterns from developing in the SFB, but cause a substantial increase in the σ within the grid region.

The work input to saturated porous media undergoing internal erosion

The mechanism of internal erosion in porous media involves the microstructural evolutions induced by washing out of fine particles under different loading and seepage flow actions. Consequently, the effective stress on the solid skeleton is governed by the transition in velocity and stress of fine particles due to their detachment from the skeleton and then transport through pore channels, in addition to pore pressure. This study is to develop a formulation of work input to account for the interactions and mass exchanges between solid and fluid phases. Coupled mechanical-hydraulic erosion processes can be properly reflected through mass, momentum and energy balances based on Biot’s mixture theory of a three-phase model. This leads to three separate stress-like variables, effective stress, erosion force and hydraulic gradient, in conjugation with three strain-like variables, strain, mass loss and seepage velocity, respectively. The effective stress tensor, different from the classical form by Terzaghi due to the effect of erosion, and coupled hydro-mechanical-erosion criteria are naturally derived from the proposed work input. They consider grain scale mechanisms describing the transition of erodible particles from the solid skeleton to the fluidized state. Systematic formulations and discussions are presented to highlight the promising features of our approach.

In-Line Detection of Bed Fluidity in Gas-Solid Fluidized Beds Using Near-Infrared Spectroscopy.

A novel approach was developed to detect bed fluidity in gas-solid fluidized beds using diffuse reflectance near-infrared (NIR) spectroscopy. Because the flow dynamics of gas and solid phases are closely associated with the fluidization state, the fluidization quality can be evaluated through hydrodynamic characterization. In this study, the baseline level of NIR spectra was used to quantify the voidage of the fluidized bed. Two indicators derived from the NIR baseline fluctuation profiles were investigated to characterize bed fluidity, named bubble proportion and skewness. To establish a robust fluidity evaluation method, the relationships between the indicators and bed fluidity were investigated under different conditions firstly, including static bed height and average particle size. Then, a generalized threshold was identified to distinguish poor and good bed fluidity, ensuring that the probability of the α- and β-errors was less than 15% regardless of material conditions. The results show that both indicators were sensitive to changes in bed fluidity under the investigated conditions. The indicator of skewness was qualified to detect bed fluidity under varied conditions with a robust threshold of 1.20. Furthermore, the developed NIR method was successfully applied to monitor bed fluidity and for early warning of defluidization in a laboratory-scale fluidized bed granulation process.

Development and combustion characteristics of microwave plasma-assisted fluidized bed combustor

A novel waste treatment method that can efficiently decompose waste, suppress by-product generation, and operate at a low cost is urgently required. Herein, a microwave plasma-assisted combustor was developed and its combustion characteristics were investigated for application in solid waste treatment. The experimental conditions for obtaining good states of fluidization, mixing, and plasma formation were examined prior to the combustion experiments. Subsequently, the optimal experimental conditions, such as the filling amount of bed particles, bed particle diameter, microwave irradiation position, and microwave output, required for good combustion were achieved. Combustion experiments based on these conditions revealed that a good fluidization state is required to obtain a good combustion state in this device, although the combustion condition does not necessarily depend on the system pressure at each O2 flow rate. Comparison of the conditions with similar fluidization states at O2 flow rates of 1–4 L/min revealed a maximum fuel conversion ratio at 4 L/min owing to the combustion promotion caused by increased O2 partial pressure. The fuel did not remain in the fluidized bed combustor after the combustion experiments.

Flow rate of solids through recycle chamber of loop seal in a circulating fluidized bed

This study investigated the flow rate of solids through the recycle chamber of a loop seal in a circulating fluidized bed (CFB) at atmospheric pressure and temperature. Flow characteristics of alumina particles were measured in the downcomer, horizontal passage, recycle chamber, and riser (0.05 m i.d., 2.7 m high).As the gas velocity in the riser increased, the pressure drop in the downcomer decreased, and thus, the aeration rate required at the bottom of the supply chamber to attain the minimum fluidization state for the bed of the downcomer increased. Based on experimental data, relationships that could predict the flow rate of solids through the recycle chamber Gs,r were derived by extending the correlation for the solids flow rate through the bubbling fluidized bed that discharged solids via overflow exit. Gs,r increased in proportion to the gauge pressure at the base of the recycle chamber. When the riser was under the fast bed condition, the back pressure against the flow of solids coming from the recycle chamber to the riser appeared significantly, and Gs,r was inversely proportional to the gauge pressure at the base of the riser. The derived relationships for Gs,r were in good agreement with measured data.