Minimum spouting velocity (Ums) is one of the most important flow characteristics for proper design and operation of spouted bed reactors. Many correlations for Ums have been published since spouted bed technology w...Minimum spouting velocity (Ums) is one of the most important flow characteristics for proper design and operation of spouted bed reactors. Many correlations for Ums have been published since spouted bed technology was initiated in 1955. In this paper, a new correlation is developed for Ums based on 767 published experimental data covering both high pressure and high temperature conditions. The calculated and the measured results of Ums are in better agreement than other published correlations.展开更多
Experiments were performed on spout characteristics of a cylindrical spout-fluidized bed (I.D. = 10 cm) with different static heights and two materials (A1203 and high density polyethylene). Results of minimum spo...Experiments were performed on spout characteristics of a cylindrical spout-fluidized bed (I.D. = 10 cm) with different static heights and two materials (A1203 and high density polyethylene). Results of minimum spouting velocity obtained in this study were compared with reported correlations for both spouted and spout-fluidized beds. Considerable discrepancies were found between the values obtained using different model equations as well as with respect to experimental results. Based on the Mathur-Gishler correlation, a new correlation is proposed for calculating the minimum spouting velocity that introduces the ratio U/Umf. It was found that the minimum spouting velocity decreases with increasing fluidizing gas velocity (U/Umf). The pressure drop at the point of minimum spouting velocity is also correlated using this dimensionless group and is presented in this work. This investigation demonstrates that the use of correlations reported in the literature that focus primarily on conical bottom spouted beds are not applicable to fiat-bottom spouted and spout-fluidized beds.展开更多
This paper is devoted to outlining precisely the basic mathematics of a classical isoperimetric problem of the calculus of variations and showing how significant fluid mechanical problems in fluidization and spouting ...This paper is devoted to outlining precisely the basic mathematics of a classical isoperimetric problem of the calculus of variations and showing how significant fluid mechanical problems in fluidization and spouting can be addressed using this approach.展开更多
From experime nts, the influe nee of the physical characteristics of different bin ary mixtures of solids on the spouting regime of a pyramidal square-based spouted bed reactor is assessed. The applied methodology per...From experime nts, the influe nee of the physical characteristics of different bin ary mixtures of solids on the spouting regime of a pyramidal square-based spouted bed reactor is assessed. The applied methodology permits a more precise evaluation of the effects of the tested variables (diameter, density, sphericity) on the response variables (minimum air flows at which spouting begins and at which to maintain spouting con ditions). The associated pressure drops along the bed of particles a nd the height of the formed fountai n are analysed in each case. During the initial stages of fluidisation, binary mixtures containing different density ratios show dead zones. Segregation becomes more evident at large-size and high-density ratios. The lack of sphericity was found to be the main reason leading to blocking, channelling, and start-up problems when system failures occur. Nevertheless, the extent of segregation in all cases decreases with increasing the spouting velocity. In addition, a computational fluid dynamic model based on the discrete element method, previously validated for a single solid bed, is proposed as a tool to predict and evaluate potential segregation phenomena in binary mixtures. This model reproduced with high accuracy the encountered segregation phenomena. Its use may help define the technical limts inherent in the pyramidal spouted bed reactor.展开更多
Numerous industrial applications of spouted beds involve a mixture of granular particles, where differences in particle size, density, and shape can cause particle segregation, affecting the quality of flow and decrea...Numerous industrial applications of spouted beds involve a mixture of granular particles, where differences in particle size, density, and shape can cause particle segregation, affecting the quality of flow and decreasing product homogeneity. The aim of this study was to investigate the particle segregation and fluid dynamics of a conical spouted bed operating with a binary mixture of particles of different densities. Using glass beads and polyethylene particles with a diameter of 4 mm, we determined the effects of the mass fraction of denser particles and static bed height on the minimum spouting condition and mixture index. The pressure drop and airflow in the minimum spouting condition increased with an increase in bed height or jetsam concentration. Regarding particle segregation, the jetsam particles tended to concentrate near the bottom, at the spout–annulus interface because they have a shorter trajectory than the lighter particles in the fountain region. Jetsam-rich mixtures with high initial static bed heights exhibited more efficient particle mixing, excluding those at the bottom of the bed.展开更多
The removal of volatile organic compounds by photocatalytic degradation is one of the safest and most effective ways of removing pollutants from the air. This process is highly affected by the type of reactor, light e...The removal of volatile organic compounds by photocatalytic degradation is one of the safest and most effective ways of removing pollutants from the air. This process is highly affected by the type of reactor, light exposure, and hydrodynamics. For scale up purposes, continuous reactors with high capacity are required for treating large amounts of feedstock. In this work, two types of reactors based on different hydrodynamics, fluidized and spouted reactors, were designed to work under light irradiation inside the reactor. The efficiency of the reactors for volatile organic compound removal from high flow rates of air under Hg lamp irradiation using N-F-TiO2 photocatalyst was investigated. The performance of the fluidized bed and spouted bed were evaluated and compared at the same weight hourly space velocity of feed stream through the reactor. The results revealed that 80% of the initial acetaldehyde was removed in the fluidized bed after about 200 min, while in the spouted bed the acetaldehyde was totally removed after about 120 min.展开更多
The development of intensification technology for spouted beds has become a current research focus,and an effective way to improve the efficiency of spouted beds is to reform their structure.Although numerous studies ...The development of intensification technology for spouted beds has become a current research focus,and an effective way to improve the efficiency of spouted beds is to reform their structure.Although numerous studies have been conducted on conventional beds,there are few reviews on the comprehensive application of intensification technology for spouted beds.In this paper,we comprehensively review the role of intensification technology in spouted beds for use in hydrodynamics,drying,desulfurization,pyrolysis,coating,biomass and waste gasification,and biomass drying from the perspective of experiment and simulation.Finally,potential problems and challenges in current spouted-bed research are summarized.展开更多
Optimization of draft tube position in a spouted bed reactor used for treatment of wastewater containing low concentration of heavy metals is investigated in this paper. Response surface methodology is used to optimiz...Optimization of draft tube position in a spouted bed reactor used for treatment of wastewater containing low concentration of heavy metals is investigated in this paper. Response surface methodology is used to optimize the draft tube height, the draft tube width and the gap between the bottom of the draft tube and the inlet nozzle. It is observed that the draft tube with a height of 60 millimeter, width of 12 millimeter and the gap of 13 millimeter between its bottom and inlet nozzle, results in optimum value of minimum spouting velocity, measured 45 cubic centimeter per second (2.7 Liter per minute) .展开更多
In order to grasp the particle flow characteristics and energy consumption of industrial fluidized spouted beds,we conduct numerical simulations on the basis of a Computational Particle Fluid Dynamics(CPFD)approach.In...In order to grasp the particle flow characteristics and energy consumption of industrial fluidized spouted beds,we conduct numerical simulations on the basis of a Computational Particle Fluid Dynamics(CPFD)approach.In particular,the traction model of Wen-Yu-Ergun is used and different inlet conditions are considered.Using a low-speed fluidizing gas,the flow state of the particles is better and the amount of particles accumulated at the bottom of the bed wall becomes smaller.For the same air intake,the energy loss of a circular nozzle is larger than that of a square nozzle.展开更多
The spouted bed has been used in the coating process of high-density nuclear fuel particle.The particle fluidization behaviors in pseudo-2D and 3D spouted beds were simulated and validated.The effects of four independ...The spouted bed has been used in the coating process of high-density nuclear fuel particle.The particle fluidization behaviors in pseudo-2D and 3D spouted beds were simulated and validated.The effects of four independent variables(cone angle,particle density,inlet gas velocity,and particle loading)on particle fluidization behaviors in the 3D spouted bed were investigated systematically.The cone angle effect on fluidization mechanism was studied quantitatively first time.A new fluidization quality index was proposed based on the particle entrainment principle,and an extreme value was obtained when the cone angle was 60°,considered to be the optimum value for the 3D conical spouted bed.It was indicated the gas–solid contact efficiency can be kept up if the gas velocity was proportional to ρ_(p)^(0.65) and N_(p)^(0.78) when the particle density or loading was increased.These results will be useful for geometry and operation parameters design of the 3D conical spouted bed and helpful for developing the fluidization mechanism of high-density particles.展开更多
On a cold spouted fluidized bed,this study compares the characteristic differences in intrinsic mode function(IMF)energy and Hilbert–Huang spectrum between the spout zone and annulus zone under different combinations...On a cold spouted fluidized bed,this study compares the characteristic differences in intrinsic mode function(IMF)energy and Hilbert–Huang spectrum between the spout zone and annulus zone under different combinations of spouted gas and fluidized gas flow rates for five typical flow patterns.The energy distribution characteristics under different flow patterns are also analyzed.The Hilbert–Huang spectrum and IMF energy of pressure difference signals exhibit distinct variations in different zones as the flow pattern changes.Moreover,there exists a correlation between the energy in the middle-frequency range and the flow pattern.Leveraging the K-means algorithm,the middle-frequency range energy of IMFs in the spout zone and annulus zone is subjected to clustering analysis,leading to the identification of partition boundaries for each flow pattern.Based on this,a flow pattern identification method of spouted fluidized bed coupled with middle-frequency range energy in spout zone and annulus zone is proposed,which has very high identification accuracy.展开更多
The hydrodynamic behaviour of the spouted bed in the pharmaceutical industries has been found to be less addressed.The present paper has focused on the hydrodynamic characteristics of a spouted bed where the Cellets^(...The hydrodynamic behaviour of the spouted bed in the pharmaceutical industries has been found to be less addressed.The present paper has focused on the hydrodynamic characteristics of a spouted bed where the Cellets^(TM)(Ph.Eur./USP)is adopted as the bed material.Experiments are carried out with three different static bed heights(H_(0))of shallow depth(2D_(i)≤H_(0)<3D_(i))using two different particle sizes.The spouted bed employed with D_(i)/D_(0) of 5 has given the experimental information on external spouting(Ues)by mapping the pressure drop,and fountain height(H_(f))against the superficial gas velocity(U_(g))is rep-resented with the image contours,which show the intrinsic behaviour.All the 1000 μm and 700 μm particles have been found to exhibit symmetric and asymmetric spouting.With increasing U_(g),the fully suspended particles are limited to a certain height in the freeboard region due to the gas-solid cross-flow,which implies the clusters have identified with the image processing method.展开更多
A CFD-DEM reaction coupling model was established to simulate UF_(4) fluorination process,in which heat and mass transfer,heterogeneous chemical reaction,and particle shrinkage model were considered.The gas behavior w...A CFD-DEM reaction coupling model was established to simulate UF_(4) fluorination process,in which heat and mass transfer,heterogeneous chemical reaction,and particle shrinkage model were considered.The gas behavior was described by the conservation laws of mass,momentum,and energy.The solid phase is modeled with the discrete element method,considering the gas-solid interphase force,contact force,heat transfer,and chemical reaction models based on the discretized surface.Each particle can be individually tracked and associated with specific physical properties.The proposed CFD-DEM reaction coupling model based on particle shrinking reaction model with discretized surface was validated by the experimental and literature results at first.Then a multistage conical spouted bed was proposed and the process of UF_(4) fluoridation reaction in it was investigated.The fluidization characteristics and the con-centration distribution of gaseous products in the spouted bed with an extended gas velocity range were obtained and analyzed.In addition,the effects of different parameters,such as superficial gas velocity,temperature,fluorine concentration,on fluoridation rate and the fluorine conversion rate were inves-tigated based on the proposed CFD-DEM reaction coupling model.The results obtained in this work are beneficial for method development of the chemical reaction simulation research in particle scale using the CFD-DEM model,and useful for operation and equipment parameters design of the uranium tetra-fluoride fluorinate industrial process in the future.展开更多
Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literat...Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literature,the number of axial gas mixing studies in conical and conical-cylindrical spouted beds is very limited and all axial mixing studies were carried out with relatively light particles(ρp≤2500 kg/m^(3)).Therefore,the objective of this study was to generate experimental data that can be used to explain the gas axial mixing behavior in conical spouted beds operating with both low-and high-density particles.Experiments were conducted in two(γ=30°,60°)conical spouted beds with three different types of particles:zirconia(ρp=6050 kg/m^(3)),zirconia toughened alumina(ρp=3700 kg/m^(3))and glass beads(ρp=2460 kg/m^(3)).In order to be able to compare experimental data obtained at different conditions,a 1-D convection-diffusion gas mixing model originally developed by San Joséet al.(1995)was implemented to determine the axial dispersion coefficients.The results show that the axial dispersion coefficients range between m^(2)/s and m^(2)/s,increase with superficial gas velocity and are higher than the corresponding dispersion coefficients of fixed beds,lower than the dispersion coefficients of fluidized beds and in the same range with the cylindrical spouted beds reported in the literature.The corresponding Peclet numbers were in the range of 0.6–7.8 for all operating conditions and slightly higher Peclet numbers were obtained with glass beads indicating the relative importance of gas convective transport over gas dispersion for light particles compared to heavy particles.展开更多
Using a high-viscosity Newtonian fluid, glycerol, an experimental investigation was carried out to evaluate the stable spouting regime in conical spouted beds using four particle mixtures: a reference (monoparticles...Using a high-viscosity Newtonian fluid, glycerol, an experimental investigation was carried out to evaluate the stable spouting regime in conical spouted beds using four particle mixtures: a reference (monoparticles), a binary mixture, two ternary mixtures with flat and Gaussian distributions respectively. The mixtures were selected for particle diameters (dp) ranging from 1.09 to 4.98 mm and particle diameter ratios (dpL/dps) ranging from 1.98 to 4.0. Experimental data show that pressure fluctuation signals of the bed, as indicated by changes in their standard deviations, provide suitable information to identify the range of operational conditions for stable spouting. However, the analysis of skewness of curves of pressure fluctuation as a function of air velocity appears not sufficient to identify a particular flow regime. For glycerol in the spouting regime, the standard deviation is noted to increase with increasing glycerol concentration due to the growth of interparticle forces. The implications of these research findings on the drying of suspensions in conical spouted beds using glass bead mixtures are also discussed.展开更多
A novel technique for the measurement of the coating layer thickness of fine particles was developed in this work based on cross-sectioning of micrometre-sized single coated particles using focused ion beam (FIB) mill...A novel technique for the measurement of the coating layer thickness of fine particles was developed in this work based on cross-sectioning of micrometre-sized single coated particles using focused ion beam (FIB) milling. This technique was tested on two batches of aerogel particles coated with thin coatings in a spouted bed. The FIB milling procedure consisted of two steps. First, the desired part of the coated particle was removed using a high ion beam current. The resulting cross-sectioned area was then polished using a lower ion beam current to make the cross-section clearly visible. The FIB milling process was controlled with simultaneous scanning electron microscopy (SEM). Afterwards, the coating layer thickness was evaluated using the SEM images. The coating layer was successfully applied on the porous aerogel microparticles in the spouted bed. The coating uniformity of the highly porous particles increased with increasing sprayed coating solution amount, with up to 91% of the particle pores being covered. The FIB-cross-sectioning technique using an ion beam of 2.50 nA for the first milling and 0.43 nA for polishing of the surface resulted in successful generation of cross-sections of representative particles with a visible particle core and coating layer. A coating layer thickness of approximately 700 nm was achieved on particles with sizes of below 45 μm.展开更多
Foxtail millet (Setaria italica) is one of the most valuable species in economic terms in the genus Setaria and plays an important role in human nutrition, animal feed, and agriculture. The present study described c...Foxtail millet (Setaria italica) is one of the most valuable species in economic terms in the genus Setaria and plays an important role in human nutrition, animal feed, and agriculture. The present study described chemical, physical, and quality aspects of seeds of foxtail millet. Furthermore, the fluid-dynamic behavior of the seeds was evaluated in a conical spouted bed, which has advantages in terms of promoting the cyclic and regular movement of the seed particles. Dynamic parameters of spouting (minimum spouting veloc- ity, stable and peak pressure drop) were determined and compared with those obtained from empirical correlations available in the literature. The results obtained from physical characterization showed that the seeds can be classified as belonging to Group D of Geldart, having a non-rough surface, mean diameter of 1.75 mm, and sphericity of 0.74. Fluid-dynamics analysis showed that the seeds are suitable for processing in a spouted bed, which is in agreement with the results of particle physical characterization.展开更多
The flow of pharmaceutical pellets in a Wiirster fluid bed (WFB) was characterized by a frequency domain analysis of pressure fluctuations. Pellets with a diameter of 0.780 mm and density of 1.225 kg/m^3 were used in ...The flow of pharmaceutical pellets in a Wiirster fluid bed (WFB) was characterized by a frequency domain analysis of pressure fluctuations. Pellets with a diameter of 0.780 mm and density of 1.225 kg/m^3 were used in the experiments. Different flow structures were identified in the bed, including bulk movement of pellets in the annulus (f<5Hz), bulk movement of pellets inside the draft tube and bulk horizontal movement of pellets through the entrainment zone (5 </<15 Hz), and clustering (15<f< 145 Hz). The minimum spouting velocity was also measured experimentally. Effects of bed height, distanee of the entrainment zone, and distributor hole pitch on minimum spouting velocity were investigated. It was Found that the minimum spouting velocity increased with increasing bed height and distance of the entrainment zone while it decreased w ith in creasing distributor hole pitch. A correlation was developed for estimating the minimum spouting velocity in WFBs containing pharmaceutical pellets. The correlation fit the experimental data satisfactorily. Studying the WFB hydrodynamics and determining the minimum spouting velocity provides information that can be used to properly design, operate, and scale up such systems.展开更多
An improved and efficient DEM-CFD approach is developed for spouted beds. A nonlinear Discrete Element Method (DEM), with a concept of spring, dash-pot and friction slider, is used for tracing the movement of each i...An improved and efficient DEM-CFD approach is developed for spouted beds. A nonlinear Discrete Element Method (DEM), with a concept of spring, dash-pot and friction slider, is used for tracing the movement of each individual particle. The gas flow is described by a set of reorganized governing equations. Two phases are coupled through contributions due to effects of porosity, viscosity and drag. All equations are solved with the commercial package Fluent with an implementation of User Defined Functions (UDF). To validate the improved model, a two-dimensional conical-base spouted bed is chosen as a case study. An unstructured mesh system is adopted instead of regular grid system. The simulation also takes the Saffman force and Magnus effect into account. The calculation results show good agreement with the experimental observations which are taken from the literature.展开更多
Although numerical models such as the computational fluid dynamics–discrete element method (CFD–DEM) have enabled the accurate simulation of laboratory-scale apparatuses, the application of these methods to large-sc...Although numerical models such as the computational fluid dynamics–discrete element method (CFD–DEM) have enabled the accurate simulation of laboratory-scale apparatuses, the application of these methods to large-scale apparatuses with many particles and time scales ranging from minutes to hours remains a challenge. The recently developed recurrence CFD (rCFD) method seeks to overcome these issues in pseudo-periodic processes by extrapolating globally recurring patterns in a physically meaningful way and describing the transport and interaction of passive scalars using Lagrangian tracers. Spouted beds represent an interesting target because of the associated variety of flow regimes. They can be effectively described by CFD–DEM on the time scale of tens of seconds, whereas industrially relevant processes typically take hours. In this contribution, we established the validity of applying the Lagrangian rCFD method to spouted beds by demonstrating the accurate reproduction of the particle residence time distribution in a fictitious spray zone. The deposition of spray droplets onto tracer particles was simulated for 1 h, and the particle surface coverage distribution was estimated using a statistical approach for both an unstabilized prismatic spouted bed and one stabilized by draft plates.展开更多
基金the National Natural Science Foundation of China through the program "Time and Spatial Multi-Scale Interactions in Chemical Engineering and Their Effects" (Grant No. 20490201).
文摘Minimum spouting velocity (Ums) is one of the most important flow characteristics for proper design and operation of spouted bed reactors. Many correlations for Ums have been published since spouted bed technology was initiated in 1955. In this paper, a new correlation is developed for Ums based on 767 published experimental data covering both high pressure and high temperature conditions. The calculated and the measured results of Ums are in better agreement than other published correlations.
文摘Experiments were performed on spout characteristics of a cylindrical spout-fluidized bed (I.D. = 10 cm) with different static heights and two materials (A1203 and high density polyethylene). Results of minimum spouting velocity obtained in this study were compared with reported correlations for both spouted and spout-fluidized beds. Considerable discrepancies were found between the values obtained using different model equations as well as with respect to experimental results. Based on the Mathur-Gishler correlation, a new correlation is proposed for calculating the minimum spouting velocity that introduces the ratio U/Umf. It was found that the minimum spouting velocity decreases with increasing fluidizing gas velocity (U/Umf). The pressure drop at the point of minimum spouting velocity is also correlated using this dimensionless group and is presented in this work. This investigation demonstrates that the use of correlations reported in the literature that focus primarily on conical bottom spouted beds are not applicable to fiat-bottom spouted and spout-fluidized beds.
文摘This paper is devoted to outlining precisely the basic mathematics of a classical isoperimetric problem of the calculus of variations and showing how significant fluid mechanical problems in fluidization and spouting can be addressed using this approach.
文摘From experime nts, the influe nee of the physical characteristics of different bin ary mixtures of solids on the spouting regime of a pyramidal square-based spouted bed reactor is assessed. The applied methodology permits a more precise evaluation of the effects of the tested variables (diameter, density, sphericity) on the response variables (minimum air flows at which spouting begins and at which to maintain spouting con ditions). The associated pressure drops along the bed of particles a nd the height of the formed fountai n are analysed in each case. During the initial stages of fluidisation, binary mixtures containing different density ratios show dead zones. Segregation becomes more evident at large-size and high-density ratios. The lack of sphericity was found to be the main reason leading to blocking, channelling, and start-up problems when system failures occur. Nevertheless, the extent of segregation in all cases decreases with increasing the spouting velocity. In addition, a computational fluid dynamic model based on the discrete element method, previously validated for a single solid bed, is proposed as a tool to predict and evaluate potential segregation phenomena in binary mixtures. This model reproduced with high accuracy the encountered segregation phenomena. Its use may help define the technical limts inherent in the pyramidal spouted bed reactor.
文摘Numerous industrial applications of spouted beds involve a mixture of granular particles, where differences in particle size, density, and shape can cause particle segregation, affecting the quality of flow and decreasing product homogeneity. The aim of this study was to investigate the particle segregation and fluid dynamics of a conical spouted bed operating with a binary mixture of particles of different densities. Using glass beads and polyethylene particles with a diameter of 4 mm, we determined the effects of the mass fraction of denser particles and static bed height on the minimum spouting condition and mixture index. The pressure drop and airflow in the minimum spouting condition increased with an increase in bed height or jetsam concentration. Regarding particle segregation, the jetsam particles tended to concentrate near the bottom, at the spout–annulus interface because they have a shorter trajectory than the lighter particles in the fountain region. Jetsam-rich mixtures with high initial static bed heights exhibited more efficient particle mixing, excluding those at the bottom of the bed.
文摘The removal of volatile organic compounds by photocatalytic degradation is one of the safest and most effective ways of removing pollutants from the air. This process is highly affected by the type of reactor, light exposure, and hydrodynamics. For scale up purposes, continuous reactors with high capacity are required for treating large amounts of feedstock. In this work, two types of reactors based on different hydrodynamics, fluidized and spouted reactors, were designed to work under light irradiation inside the reactor. The efficiency of the reactors for volatile organic compound removal from high flow rates of air under Hg lamp irradiation using N-F-TiO2 photocatalyst was investigated. The performance of the fluidized bed and spouted bed were evaluated and compared at the same weight hourly space velocity of feed stream through the reactor. The results revealed that 80% of the initial acetaldehyde was removed in the fluidized bed after about 200 min, while in the spouted bed the acetaldehyde was totally removed after about 120 min.
基金supported by the National Natural Science Foundation of China(22178286)Shaanxi Qin Chuangyuan“scientist and engineer”team construction project(2022KXJ-041).
文摘The development of intensification technology for spouted beds has become a current research focus,and an effective way to improve the efficiency of spouted beds is to reform their structure.Although numerous studies have been conducted on conventional beds,there are few reviews on the comprehensive application of intensification technology for spouted beds.In this paper,we comprehensively review the role of intensification technology in spouted beds for use in hydrodynamics,drying,desulfurization,pyrolysis,coating,biomass and waste gasification,and biomass drying from the perspective of experiment and simulation.Finally,potential problems and challenges in current spouted-bed research are summarized.
文摘Optimization of draft tube position in a spouted bed reactor used for treatment of wastewater containing low concentration of heavy metals is investigated in this paper. Response surface methodology is used to optimize the draft tube height, the draft tube width and the gap between the bottom of the draft tube and the inlet nozzle. It is observed that the draft tube with a height of 60 millimeter, width of 12 millimeter and the gap of 13 millimeter between its bottom and inlet nozzle, results in optimum value of minimum spouting velocity, measured 45 cubic centimeter per second (2.7 Liter per minute) .
基金supported by the Key Technology Research and Development Program of Zhejiang(2019C01127)the Natural Science Foundation of Zhejiang Province(LQ20E060012).
文摘In order to grasp the particle flow characteristics and energy consumption of industrial fluidized spouted beds,we conduct numerical simulations on the basis of a Computational Particle Fluid Dynamics(CPFD)approach.In particular,the traction model of Wen-Yu-Ergun is used and different inlet conditions are considered.Using a low-speed fluidizing gas,the flow state of the particles is better and the amount of particles accumulated at the bottom of the bed wall becomes smaller.For the same air intake,the energy loss of a circular nozzle is larger than that of a square nozzle.
基金funded by National Youth Talent Support Program(grant number 20224723061)National major S&T Project(grant number ZX06901).
文摘The spouted bed has been used in the coating process of high-density nuclear fuel particle.The particle fluidization behaviors in pseudo-2D and 3D spouted beds were simulated and validated.The effects of four independent variables(cone angle,particle density,inlet gas velocity,and particle loading)on particle fluidization behaviors in the 3D spouted bed were investigated systematically.The cone angle effect on fluidization mechanism was studied quantitatively first time.A new fluidization quality index was proposed based on the particle entrainment principle,and an extreme value was obtained when the cone angle was 60°,considered to be the optimum value for the 3D conical spouted bed.It was indicated the gas–solid contact efficiency can be kept up if the gas velocity was proportional to ρ_(p)^(0.65) and N_(p)^(0.78) when the particle density or loading was increased.These results will be useful for geometry and operation parameters design of the 3D conical spouted bed and helpful for developing the fluidization mechanism of high-density particles.
基金Financial support from the Natural Science Foundation of Anhui Province,China(grant No.2108085ME161)the University Natural Science Research Project of Anhui Province,China(grant No.2022AH050317)+1 种基金Wuhu Technology and Innovation Research Institute Fund(grant No.RZ2300000872)Anhui Province University Excellent Talents Training Funding Project(grant No.gxyqZD2021108)are gratefully acknowledged.
文摘On a cold spouted fluidized bed,this study compares the characteristic differences in intrinsic mode function(IMF)energy and Hilbert–Huang spectrum between the spout zone and annulus zone under different combinations of spouted gas and fluidized gas flow rates for five typical flow patterns.The energy distribution characteristics under different flow patterns are also analyzed.The Hilbert–Huang spectrum and IMF energy of pressure difference signals exhibit distinct variations in different zones as the flow pattern changes.Moreover,there exists a correlation between the energy in the middle-frequency range and the flow pattern.Leveraging the K-means algorithm,the middle-frequency range energy of IMFs in the spout zone and annulus zone is subjected to clustering analysis,leading to the identification of partition boundaries for each flow pattern.Based on this,a flow pattern identification method of spouted fluidized bed coupled with middle-frequency range energy in spout zone and annulus zone is proposed,which has very high identification accuracy.
文摘The hydrodynamic behaviour of the spouted bed in the pharmaceutical industries has been found to be less addressed.The present paper has focused on the hydrodynamic characteristics of a spouted bed where the Cellets^(TM)(Ph.Eur./USP)is adopted as the bed material.Experiments are carried out with three different static bed heights(H_(0))of shallow depth(2D_(i)≤H_(0)<3D_(i))using two different particle sizes.The spouted bed employed with D_(i)/D_(0) of 5 has given the experimental information on external spouting(Ues)by mapping the pressure drop,and fountain height(H_(f))against the superficial gas velocity(U_(g))is rep-resented with the image contours,which show the intrinsic behaviour.All the 1000 μm and 700 μm particles have been found to exhibit symmetric and asymmetric spouting.With increasing U_(g),the fully suspended particles are limited to a certain height in the freeboard region due to the gas-solid cross-flow,which implies the clusters have identified with the image processing method.
基金supported by the National S&T Major Project of China(grant No.ZX06901).
文摘A CFD-DEM reaction coupling model was established to simulate UF_(4) fluorination process,in which heat and mass transfer,heterogeneous chemical reaction,and particle shrinkage model were considered.The gas behavior was described by the conservation laws of mass,momentum,and energy.The solid phase is modeled with the discrete element method,considering the gas-solid interphase force,contact force,heat transfer,and chemical reaction models based on the discretized surface.Each particle can be individually tracked and associated with specific physical properties.The proposed CFD-DEM reaction coupling model based on particle shrinking reaction model with discretized surface was validated by the experimental and literature results at first.Then a multistage conical spouted bed was proposed and the process of UF_(4) fluoridation reaction in it was investigated.The fluidization characteristics and the con-centration distribution of gaseous products in the spouted bed with an extended gas velocity range were obtained and analyzed.In addition,the effects of different parameters,such as superficial gas velocity,temperature,fluorine concentration,on fluoridation rate and the fluorine conversion rate were inves-tigated based on the proposed CFD-DEM reaction coupling model.The results obtained in this work are beneficial for method development of the chemical reaction simulation research in particle scale using the CFD-DEM model,and useful for operation and equipment parameters design of the uranium tetra-fluoride fluorinate industrial process in the future.
基金This work was carried out with the financial support of the Scientific and Technological Research Council of Turkey(Project No:MAG 115M392)。
文摘Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literature,the number of axial gas mixing studies in conical and conical-cylindrical spouted beds is very limited and all axial mixing studies were carried out with relatively light particles(ρp≤2500 kg/m^(3)).Therefore,the objective of this study was to generate experimental data that can be used to explain the gas axial mixing behavior in conical spouted beds operating with both low-and high-density particles.Experiments were conducted in two(γ=30°,60°)conical spouted beds with three different types of particles:zirconia(ρp=6050 kg/m^(3)),zirconia toughened alumina(ρp=3700 kg/m^(3))and glass beads(ρp=2460 kg/m^(3)).In order to be able to compare experimental data obtained at different conditions,a 1-D convection-diffusion gas mixing model originally developed by San Joséet al.(1995)was implemented to determine the axial dispersion coefficients.The results show that the axial dispersion coefficients range between m^(2)/s and m^(2)/s,increase with superficial gas velocity and are higher than the corresponding dispersion coefficients of fixed beds,lower than the dispersion coefficients of fluidized beds and in the same range with the cylindrical spouted beds reported in the literature.The corresponding Peclet numbers were in the range of 0.6–7.8 for all operating conditions and slightly higher Peclet numbers were obtained with glass beads indicating the relative importance of gas convective transport over gas dispersion for light particles compared to heavy particles.
文摘Using a high-viscosity Newtonian fluid, glycerol, an experimental investigation was carried out to evaluate the stable spouting regime in conical spouted beds using four particle mixtures: a reference (monoparticles), a binary mixture, two ternary mixtures with flat and Gaussian distributions respectively. The mixtures were selected for particle diameters (dp) ranging from 1.09 to 4.98 mm and particle diameter ratios (dpL/dps) ranging from 1.98 to 4.0. Experimental data show that pressure fluctuation signals of the bed, as indicated by changes in their standard deviations, provide suitable information to identify the range of operational conditions for stable spouting. However, the analysis of skewness of curves of pressure fluctuation as a function of air velocity appears not sufficient to identify a particular flow regime. For glycerol in the spouting regime, the standard deviation is noted to increase with increasing glycerol concentration due to the growth of interparticle forces. The implications of these research findings on the drying of suspensions in conical spouted beds using glass bead mixtures are also discussed.
文摘A novel technique for the measurement of the coating layer thickness of fine particles was developed in this work based on cross-sectioning of micrometre-sized single coated particles using focused ion beam (FIB) milling. This technique was tested on two batches of aerogel particles coated with thin coatings in a spouted bed. The FIB milling procedure consisted of two steps. First, the desired part of the coated particle was removed using a high ion beam current. The resulting cross-sectioned area was then polished using a lower ion beam current to make the cross-section clearly visible. The FIB milling process was controlled with simultaneous scanning electron microscopy (SEM). Afterwards, the coating layer thickness was evaluated using the SEM images. The coating layer was successfully applied on the porous aerogel microparticles in the spouted bed. The coating uniformity of the highly porous particles increased with increasing sprayed coating solution amount, with up to 91% of the particle pores being covered. The FIB-cross-sectioning technique using an ion beam of 2.50 nA for the first milling and 0.43 nA for polishing of the surface resulted in successful generation of cross-sections of representative particles with a visible particle core and coating layer. A coating layer thickness of approximately 700 nm was achieved on particles with sizes of below 45 μm.
文摘Foxtail millet (Setaria italica) is one of the most valuable species in economic terms in the genus Setaria and plays an important role in human nutrition, animal feed, and agriculture. The present study described chemical, physical, and quality aspects of seeds of foxtail millet. Furthermore, the fluid-dynamic behavior of the seeds was evaluated in a conical spouted bed, which has advantages in terms of promoting the cyclic and regular movement of the seed particles. Dynamic parameters of spouting (minimum spouting veloc- ity, stable and peak pressure drop) were determined and compared with those obtained from empirical correlations available in the literature. The results obtained from physical characterization showed that the seeds can be classified as belonging to Group D of Geldart, having a non-rough surface, mean diameter of 1.75 mm, and sphericity of 0.74. Fluid-dynamics analysis showed that the seeds are suitable for processing in a spouted bed, which is in agreement with the results of particle physical characterization.
文摘The flow of pharmaceutical pellets in a Wiirster fluid bed (WFB) was characterized by a frequency domain analysis of pressure fluctuations. Pellets with a diameter of 0.780 mm and density of 1.225 kg/m^3 were used in the experiments. Different flow structures were identified in the bed, including bulk movement of pellets in the annulus (f<5Hz), bulk movement of pellets inside the draft tube and bulk horizontal movement of pellets through the entrainment zone (5 </<15 Hz), and clustering (15<f< 145 Hz). The minimum spouting velocity was also measured experimentally. Effects of bed height, distanee of the entrainment zone, and distributor hole pitch on minimum spouting velocity were investigated. It was Found that the minimum spouting velocity increased with increasing bed height and distance of the entrainment zone while it decreased w ith in creasing distributor hole pitch. A correlation was developed for estimating the minimum spouting velocity in WFBs containing pharmaceutical pellets. The correlation fit the experimental data satisfactorily. Studying the WFB hydrodynamics and determining the minimum spouting velocity provides information that can be used to properly design, operate, and scale up such systems.
文摘An improved and efficient DEM-CFD approach is developed for spouted beds. A nonlinear Discrete Element Method (DEM), with a concept of spring, dash-pot and friction slider, is used for tracing the movement of each individual particle. The gas flow is described by a set of reorganized governing equations. Two phases are coupled through contributions due to effects of porosity, viscosity and drag. All equations are solved with the commercial package Fluent with an implementation of User Defined Functions (UDF). To validate the improved model, a two-dimensional conical-base spouted bed is chosen as a case study. An unstructured mesh system is adopted instead of regular grid system. The simulation also takes the Saffman force and Magnus effect into account. The calculation results show good agreement with the experimental observations which are taken from the literature.
文摘Although numerical models such as the computational fluid dynamics–discrete element method (CFD–DEM) have enabled the accurate simulation of laboratory-scale apparatuses, the application of these methods to large-scale apparatuses with many particles and time scales ranging from minutes to hours remains a challenge. The recently developed recurrence CFD (rCFD) method seeks to overcome these issues in pseudo-periodic processes by extrapolating globally recurring patterns in a physically meaningful way and describing the transport and interaction of passive scalars using Lagrangian tracers. Spouted beds represent an interesting target because of the associated variety of flow regimes. They can be effectively described by CFD–DEM on the time scale of tens of seconds, whereas industrially relevant processes typically take hours. In this contribution, we established the validity of applying the Lagrangian rCFD method to spouted beds by demonstrating the accurate reproduction of the particle residence time distribution in a fictitious spray zone. The deposition of spray droplets onto tracer particles was simulated for 1 h, and the particle surface coverage distribution was estimated using a statistical approach for both an unstabilized prismatic spouted bed and one stabilized by draft plates.