A method for packing irregular particles with a prescribed volume fraction is proposed.Furthermore,the generated granular material adheres to the prescribed statistical distribution and satisfies the desired complex s...A method for packing irregular particles with a prescribed volume fraction is proposed.Furthermore,the generated granular material adheres to the prescribed statistical distribution and satisfies the desired complex spatial arrangement.First,the irregular geometries of the realistic particles were obtained from the original particle images.Second,the Minkowski sum was used to check the overlap between irregular particles and place an irregular particle in contact with other particles.Third,the optimised advance front method(OAFM)generated irregular particle packing with the prescribed statistical dis-tribution and volume fraction based on the Minkowski sum.Moreover,the signed distance function was introduced to pack the particles in accordance with the desired spatial arrangement.Finally,seven biaxial tests were performed using the UDEC software,which demonstrated the accuracy and potential usefulness of the proposed method.It can model granular material efficiently and reflect the meso-structural characteristics of complex granular materials.This method has a wide range of applications where discrete modelling of granular media is necessary.展开更多
Packed bed reactors of non-spherical particles are widely used in chemical industry with the aim to obtain a high active surface area and achieve a homogeneous flow.Despite this,little is known about the arrangement o...Packed bed reactors of non-spherical particles are widely used in chemical industry with the aim to obtain a high active surface area and achieve a homogeneous flow.Despite this,little is known about the arrangement of particles within the bed and the influence of this arrangement on the fluid flow distribution.Magnetic Resonance Imaging (MRI) is a non-invasive tomographic imaging technique that allows 3D visualisation of the packing and flow structure.However,the individual particle information is not obtained using MRI.In this work we investigate different particle detection methods to retrieve the particle position and orientation from MRI images.Results show the successful reconstruction of random packing structures of various non-spherical particle shapes: ellipsoid,spherocylinder,cylinder and cube.The applicability of each method in relation to the particle shape,as well as strengths and drawbacks of each particle detection method are discussed.This paper shows the ability to reconstruct real packed beds of non-spherical particle shapes from MRI images,which opens several research opportunities in the field of chemical engineering.展开更多
The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell(SUC)and body-centred cubic(BCC)configuration of particles in packed...The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell(SUC)and body-centred cubic(BCC)configuration of particles in packed beds.The experimental setup is built in such a way that suitable and simplified boundary conditions are imposed for the corresponding numerical framework,so the simulations can be done under very similar conditions as the experiments.Accordingly,a porous plate is used for the co-flow to achieve the uniform velocity and the fully developed flow is ensured for the jet flow.The SUC and BCC particle beds consist of 3D-printed spheres,and the non-isotropy near the walls is mostly eliminated by placing half-spheres at the channel walls.The flow velocities are analysed directly at the exit of the particle bed for both beds over 36 pores for the SUC configuration and 60 pores for the BCC configuration,for particle Reynolds numbers of 200,300,and 400.Stereo particle image velocimetry is experimentally arranged in such a way that the velocities over the entire region at the exit of the packed bed are obtained instantaneously.The numerical method consists of a state-of-the-art immersed boundary method with adaptive mesh refinement.The paper presents the pore jet structure and velocity field exiting from each pore for the SUC and BCC packed particle beds.The numerical and experimental studies show a good agreement for the SUC configuration for all flow velocities.For the BCC configuration,some differences can be observed in the pore jet flow structure between the simulations and the experiments,but the general flow velocity distribution shows a good overall agreement.The axial velocity is generally higher for the pores located near the centre of the packed bed than for the pores near the wall.In addition,the axial velocities are observed to increase near the peripheral pores of the packed bed.This behaviour is predominant for the BCC configuration as compared to the SUC configuration.The velocities near the peripheral pores can become even higher than those at the central pores for the BCC configuration.It is shown that both the experiments as well as the simulations can be used to study the complex fluid structures inside a packed bed reactor.展开更多
The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compact...The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compaction index, denoted by a, b, c, and K, respectively） may be classified into the 2-parameter model （with a and b incorporated）, the compressible model （with a, b, and 1（incorporated）, and the 3- parameter model （with a, b, and c incorporated）. This paper evaluates these models by comparing their respective packing density predictions with the test results published in the literature. It was found that their accuracy varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, some of them become inaccurate and the errors tend to be larger at around the volumetric fractions giving maximum packing density. Relatively, the 3-parameter model is the most accurate and widely applicable.展开更多
Packed-bed reactors(PBRs)hold great promise for environmental applications,but a deeper understanding of the behavior of plasma discharge within PBRs is required.To this end,a partial-discharge alternative equivalent ...Packed-bed reactors(PBRs)hold great promise for environmental applications,but a deeper understanding of the behavior of plasma discharge within PBRs is required.To this end,a partial-discharge alternative equivalent circuit for PBRs was established in this work.Dielectric particles(glass beads or glass sand)were used to place focus on the effects of the particle size and shape on the partial discharge behavior of the oxygen PBRs.Some electrical characterizations were explored(e.g.the effective dielectric capacitance,partial discharge coefficient,and corrected burning voltage)that may differ from long-standing interpretations.The findings indicate that the suppressive effect of surface discharge on filament discharge is stronger with the decrease of the particle size.For partial discharge,the effective dielectric capacitance is always less than the dielectric capacitance.The corrected burning voltage and partial discharge tendency increase with the decrease of the particle size.As compared to an empty reactor,the average electric field in the PBR was found to be improved by 3–4 times,and the ozone energy efficiency and production were promoted by more than 20%and 15%,respectively.The plasma processing capacity can therefore be improved by choosing a relatively large size or a complex,irregularly-shaped packing material that is suitable for the discharge gap.展开更多
Methods and procedures of three-dimensional （3D） characterization of the pore structure features in the packed ore particle bed are focused. X-ray computed tomography was applied to deriving the cross-sectional imag...Methods and procedures of three-dimensional （3D） characterization of the pore structure features in the packed ore particle bed are focused. X-ray computed tomography was applied to deriving the cross-sectional images of specimens with single particle size of 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 ram. Based on the in-house developed 3D image analysis programs using Matlab, the volume porosity, pore size distribution and degree of connectivity were calculated and analyzed in detail. The results indicate that the volume porosity, the mean diameter of pores and the effective pore size （d50） increase with the increasing of particle size. Lognormal distribution or Gauss distribution is mostly suitable to model the pore size distribution. The degree of connectivity investigated on the basis of cluster-labeling algorithm also increases with increasing the particle size approximately.展开更多
The vanadium-titanium magnetite concentrate from Panxi region of China was pretreated by high pressure roller grinding（ HPRG） and then used in pelletization. Size distribution change of the vanadiumtitanium magnetit...The vanadium-titanium magnetite concentrate from Panxi region of China was pretreated by high pressure roller grinding（ HPRG） and then used in pelletization. Size distribution change of the vanadiumtitanium magnetite concentrate after HPRG and the improvement of its green pellet strength were investigated. The results indicated that,besides the increase of fine particles,the vanadium-titanium magnetite concentrate after HPRG had a smaller size ratio of fine particle to coarse particle of 0. 126,meaning a lower porosity,compared with the size ratio of raw material of 0. 157. The concentrate particles were more closely packed when there was a smaller size ratio of fine particle to coarse particle. The particle packing in the green pellets was closer after HPRG,which strengthened the green pellets with an average drop number of 5. 1（ drop height of 0. 5 m） and average compressive strength of 13. 1 N per pellet of 11 mm in diameter.展开更多
Two packing structures with the maximum packing densities of 0.64 and 0.74 for the amorphous state and crystalline state, respectively, were numerically reproduced in the packing densification of equal spheres subject...Two packing structures with the maximum packing densities of 0.64 and 0.74 for the amorphous state and crystalline state, respectively, were numerically reproduced in the packing densification of equal spheres subjected to one- dimensional and three-dimensional vibrations using the discrete element method （DEM）, and the results were physically validated. These two packing structures were analyzed in terms of coordination number （CN）, radial distribution function （RDF）, angular distribution function （ADF）, and pore size distribution （Voronoi/Delaunay tessellation）. It is shown that CN distributions have the peak values of 7 and 12 for the amorphous state and crystalline state, respectively. RDF and ADF distributions show isolated peaks and orientation preferences for the crystalline state, indicating the long range and angle correlation among particles commonly observed in the crystalline state. Voronoi/Delaunay tessellation also shows smaller and narrower pore size distribution for the crystalline state.展开更多
Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of partic...Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.展开更多
Particle based models of composite anodes are useful tools for exploring the behavior of SOFC systems. As part of our efforts to develop models for understanding fuel cells, we have been building models of Ni-YSZ comp...Particle based models of composite anodes are useful tools for exploring the behavior of SOFC systems. As part of our efforts to develop models for understanding fuel cells, we have been building models of Ni-YSZ composite anodes using experimentally measured particle size distributions. The objectives of this study were to characterize the percolation threshold and conductivity of these models in comparison to simpler mono dispersed and biphasic particle size distributions from the literature. We found that the average values for the onset of percolation and the measured conductivity of the models with experimentally measured particle size distributions are similar to those for the simple distributions and the experimentally measured distributions. For all of the configurations evaluated, the onset of percolation in the Nickel phase occurred at a solid fraction of Nickel between 20% and 25%. This corresponded almost exactly to the point at which the coordination number between Nickel phase particles reached 2.2. The significant finding was that the variation in the value for the conductivity, as measured by the standard deviation of the results, was several orders of magnitude higher than for the simpler systems. We explored the validity of our assumptions, specifically the assumption of random particle placement, by building a particle model directly from FIB-SEM data. In this reconstruction, it was clear that the location of particles was not random. Particles of the same type and size had much likelihood of contact higher than would indicated by random location.展开更多
In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemic...In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.展开更多
Metastability,disorder and jamming are the typical characteristics of amorphous systems,while the related structure changes remain unclear.Sphere packing is often used as a structure model for amorphous and crystallin...Metastability,disorder and jamming are the typical characteristics of amorphous systems,while the related structure changes remain unclear.Sphere packing is often used as a structure model for amorphous and crystalline states.In this article,sphere packing systems with packing densities ranging from 0.50 to 0.74 were simulated by using Discrete Element Method(DEM),and the obtained packing structures were assessed to investigate the densification process and jamming properties.An order parameter that can effectively distinguish the order and disorder of packing structures was proposed based on the distribution characteristics of jamming angles.Then the evolution of jamming characteristics during the transition from Random Loose Packing(RLP)to Random Close Packing(RCP)and the jamming-jamming relations of different packing structures were demonstrated.On this basis,a correlation between order-jamming-metastable states from the microscopic structural perspective was established,which is of valuable theoretical and practical implications for the characterization and synthesis of crystalline and amorphous materials.展开更多
The particle packed bed energy storage system has advantages such as low costs and wide temperature ranges,which can be combined with solar thermal power generation systems to solve the inherent volatility and discont...The particle packed bed energy storage system has advantages such as low costs and wide temperature ranges,which can be combined with solar thermal power generation systems to solve the inherent volatility and discontinuity of renewable energy.Developing new materials with low costs and excellent storage performances is one of the eternal research hotspots in the field of energy storage.This paper innovatively uses sintered ore particles as energy storage material and studies the effect of particle size on the airflow resistance characteristics,energy storage characteristics,and thermocline evolution characteristics of the packed bed through thermal energy storage experiments.The results indicate that for the particles in the macro scale,the smaller the particle,the lower the absolute permeability of the bed and the greater the airflow resistance.The packed bed with smaller particles has a larger specific surface area,larger bulk mass,and smaller bed voidage.Therefore,the packed beds with smaller particles have better thermocline characteristics,less irreversible loss,and can achieve higher thermal efficiency and higher exergy efficiency in the heat storage cycle.The cycle thermal efficiency in packed beds with 25-40 mm,16-25 mm,and 10-16 mm particles is 53.58%,56.27%,and 57.60%,respectively,and the cycle exergy efficiency is 61.81%,69.25%,and 74.13%,respectively.Moreover,this paper also studies the effect of discharging airflow rates on thermal storage performance.The experimental results indicate that suitable discharging strategies should be selected based on different heat demands.展开更多
Solid particles instead of molten salt as a heat storage medium for extracted steam energy storage are essential in thermal power flexibility retrofit. This study constructs a charge-discharge experimental device usin...Solid particles instead of molten salt as a heat storage medium for extracted steam energy storage are essential in thermal power flexibility retrofit. This study constructs a charge-discharge experimental device using by-products from the steel industry as heat storage materials, similar to a battery cell, which is easily scalable and accomplishes the steam-solid particle-steam energy conversion. Investigation parameters include temperature distribution, power variation, and cycle efficiency for different charging and discharging modes. Results indicate that the charging mode II outperforms mode I in temperature uniformity, charging flow rate, and pressure loss, yielding higher charging power and total convective heat transfer coefficients at 13 kW and 275 W/(m^(2) K), respectively. The pilot device demonstrates commendable insulating properties. Its heat dissipation rate is approximately 33.33%, which surpasses that of reported thermal storage devices. Moreover, the mode II exhibits superior temperature non-uniformity during heat release, ensuring that 40 kg/h of superheated steam at 220 ℃ can be produced continuously for 5 min. The cycling efficiency is noteworthy, reaching 65% in low flow rate discharge, accompanied by 79% charging efficiency and 82% discharging efficiency. A temperature difference cloud map elucidates the primary phase change region, emphasizing preheating, evaporation, and superheating segments. Experimental results provide new ideas for combining waste elimination in the steel industry and energy storage in thermal power plants.展开更多
Coated sands are used extensively for additive manufacturing sand molds in the metal casting process, and the packing structure changes caused by the resin flow promote the shrinkage and deformation of the part. Durin...Coated sands are used extensively for additive manufacturing sand molds in the metal casting process, and the packing structure changes caused by the resin flow promote the shrinkage and deformation of the part. During the coated sand heating, the resin on the surface flowing to the contact points of the particles forms the resin neck and causes particles to pack close to each other. In this work, the diameters of the coated ceramsite sand before and after heating were measured based on in-situ experimental observations with image measuring apparatus and blue laser, to obtain the relationship between resin coating thickness and the particle diameter. The particle packing model was established to describe the particles＇ achievement of a stable state one by one. A re-packing simulation was then performed after reducing the particle diameter according to the resin coating thickness, to obtain the shrinkage ratios at different particle size distributions. It was found that the resin coating thickness increased from 0.8 to 2.3 IJm as the particle diameter increased from 107 to 500 IJm, for the coated ceramsite sand with the resin content of 2wt.%; the shrinkage ratio decreased first and then increased as the particle diameter increased. The experimental minimum shrinkage ratio was 3.28%, and the corresponding particle diameter was 300-375 IJm, while the minimum shrinkage ratio obtained by simulation was 3.43%, and the corresponding particle diameter was 214-300 IJm. After mixing the five groups proportionally, the shrinkage ratios of the simulation and experiment dropped to 2.81% and 3.04%, respectively, indicating the best results.展开更多
To compensate for the shortcomings of the thermal and catalytic regeneration of the diesel particulate filter(DPF),a self-designed packed-bed dielectric barrier discharge(DBD)reactor for DPF regeneration was developed...To compensate for the shortcomings of the thermal and catalytic regeneration of the diesel particulate filter(DPF),a self-designed packed-bed dielectric barrier discharge(DBD)reactor for DPF regeneration was developed.The DBD reactor with the main active substance of nonthermal plasma(NTP)as the target parameter was optimized by adjusting the feed gas,packing particles(material or size),and cooling water temperature.Moreover,a set of optimal working parameters(gas source,O_2;packing particles,1.2–1.4 mm ZrO_(2);and cooling water temperature,20℃)was selected to evaluate the effect of different O_(3) concentrations on DPF regeneration.The research results showed that selecting packing particles with high dielectric constant and large particles,as well as reducing the cooling water temperature,with oxygen as the feed gas,contributed to an increase in O_(3) concentration.During DPF regeneration,the following changes were observed:the power of the NTP reactor decreased to lower than 100 W,the O_(3) concentration increased from 15 g m^(-3) to 45 g m^(-3),the CO and CO_2 volume fractions of the particulate matter decomposition products increased,and the peak regeneration temperature increased to 173.4℃.The peak temperature arrival time was 60 min earlier,indicating that the regeneration rate of DPF increased with the increase in O_(3) concentration.However,the O_(3) utilization rate(the amount of carbon deposit removed per unit volume O_(3))initially increased and then decreased;when the O_(3) concentration was set to 25 g m^(-3),the highest O_(3) utilization rate was reached.The packed-bed DBD technology contributed to the increase in the concentration of NTP active substances and the regeneration efficiency of DPF.It provides a theoretical and experimental basis for high-efficiency regeneration of DPF at low temperatures(<200℃).展开更多
Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration ti...Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration time, frequency, amplitude, vibration strength, container size, and the aspect ratio and spheric- ity of the particle on the packing density were analyzed and discussed. For each initial packing density with a certain aspect ratio, operating parameters were optimized to achieve much denser packing. The results indicate that the packing density initially increases with vibration time and then remains con- stant. The effects of vibration frequency and amplitude on the packing densification have similar trends, i.e. the packing density first increases with the vibration frequency or amplitude to a high value and then decreases; too large or small frequency or amplitude does not enhance densification. Increasing the container size can reduce container wall effects and help achieve a high packing density. Varying the particle aspect ratio and sphericity can lead to different dense random packing structures. Overall, based on results of the examined systems, the highest random packing density obtained in an infinite sized container can reach 0.73, which agrees well with corresponding numerical and analytical results in the literature.展开更多
Densification of mono-sized sphere packings using two-dimensional （2D） vibration was experimentally studied. The effects of vibration mode, amplitude and frequency, feeding method, and container size on packing dens...Densification of mono-sized sphere packings using two-dimensional （2D） vibration was experimentally studied. The effects of vibration mode, amplitude and frequency, feeding method, and container size on packing density were systematically analyzed. Useful results were obtained.展开更多
The packing densification of binary spherical mixtures under 3D mechanical vibration was studied experimentally. The influences of vibration frequency （ω）, volume fraction of large spheres （XL）, sphere size ratio...The packing densification of binary spherical mixtures under 3D mechanical vibration was studied experimentally. The influences of vibration frequency （ω）, volume fraction of large spheres （XL）, sphere size ratio （r, diameter ratio of small to large spheres）, and container size （D） on the random binary packing density （p） were systematically analyzed. For any given set of conditions, there exist optimal ω and XL to realize the densest random binary packing; too large or small ω and XL is not helpful for densification. The influences of both r and D on p are monotonic; either reducing r or increasing D leads to a high value of p. With all other parameters held constant, the densest random packing occurs when XL is dominant, which is in good agreement with the Furnas relation. Moreover, the highest random binary packing density obtained in our work agrees well with corresponding numerical and analytical results in the literature.展开更多
The motion and deformation of soft particles are commonly encountered and important in many appli-cations.A discrete element-embedded finite element model(DEFEM)is proposed to solve soft particle motion and deformatio...The motion and deformation of soft particles are commonly encountered and important in many appli-cations.A discrete element-embedded finite element model(DEFEM)is proposed to solve soft particle motion and deformation,which combines discrete element and finite element methods.The collisional surface of soft particles is covered by several dynamical embedded discrete elements(EDEs)to model the collisional external forces of the particles.The particle deformation,motion,and rotation are inde-pendent of each other in the DEFEM.The deformation and internal forces are simulated using the finite element model,whereas the particle rotation and motion calculations are based on the discrete element model.By inheriting the advantages of existing coupling methods,the contact force and contact search between soft particles are improved with the aid of the EDE.Soft particle packing is simulated using the DEFEM for two cases:particle accumulation along a rectangular straight wall and a wall with an inclined angle.The large particle deformation in the lower layers can be simulated using current meth-ods,where the deformed particle shape is either irregular in the marginal region or nearly hexagonal in the tightly packed central region.This method can also be used to simulate the deformation,motion,and heat transfer of non-spherical soft particles.展开更多
基金The authors would like to acknowledge the financial support provided by the National Key R&D Program of China(Grant No.2018YFC1504802)the National Natural Science Foundation of China(Grant Nos.41972266,12102230).
文摘A method for packing irregular particles with a prescribed volume fraction is proposed.Furthermore,the generated granular material adheres to the prescribed statistical distribution and satisfies the desired complex spatial arrangement.First,the irregular geometries of the realistic particles were obtained from the original particle images.Second,the Minkowski sum was used to check the overlap between irregular particles and place an irregular particle in contact with other particles.Third,the optimised advance front method(OAFM)generated irregular particle packing with the prescribed statistical dis-tribution and volume fraction based on the Minkowski sum.Moreover,the signed distance function was introduced to pack the particles in accordance with the desired spatial arrangement.Finally,seven biaxial tests were performed using the UDEC software,which demonstrated the accuracy and potential usefulness of the proposed method.It can model granular material efficiently and reflect the meso-structural characteristics of complex granular materials.This method has a wide range of applications where discrete modelling of granular media is necessary.
文摘Packed bed reactors of non-spherical particles are widely used in chemical industry with the aim to obtain a high active surface area and achieve a homogeneous flow.Despite this,little is known about the arrangement of particles within the bed and the influence of this arrangement on the fluid flow distribution.Magnetic Resonance Imaging (MRI) is a non-invasive tomographic imaging technique that allows 3D visualisation of the packing and flow structure.However,the individual particle information is not obtained using MRI.In this work we investigate different particle detection methods to retrieve the particle position and orientation from MRI images.Results show the successful reconstruction of random packing structures of various non-spherical particle shapes: ellipsoid,spherocylinder,cylinder and cube.The applicability of each method in relation to the particle shape,as well as strengths and drawbacks of each particle detection method are discussed.This paper shows the ability to reconstruct real packed beds of non-spherical particle shapes from MRI images,which opens several research opportunities in the field of chemical engineering.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 422037413-TRR 287Gefördert durch die Deutsche Forschungsgemeinschaft(DFG)-Projektnummer 422037413-TRR 287.
文摘The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell(SUC)and body-centred cubic(BCC)configuration of particles in packed beds.The experimental setup is built in such a way that suitable and simplified boundary conditions are imposed for the corresponding numerical framework,so the simulations can be done under very similar conditions as the experiments.Accordingly,a porous plate is used for the co-flow to achieve the uniform velocity and the fully developed flow is ensured for the jet flow.The SUC and BCC particle beds consist of 3D-printed spheres,and the non-isotropy near the walls is mostly eliminated by placing half-spheres at the channel walls.The flow velocities are analysed directly at the exit of the particle bed for both beds over 36 pores for the SUC configuration and 60 pores for the BCC configuration,for particle Reynolds numbers of 200,300,and 400.Stereo particle image velocimetry is experimentally arranged in such a way that the velocities over the entire region at the exit of the packed bed are obtained instantaneously.The numerical method consists of a state-of-the-art immersed boundary method with adaptive mesh refinement.The paper presents the pore jet structure and velocity field exiting from each pore for the SUC and BCC packed particle beds.The numerical and experimental studies show a good agreement for the SUC configuration for all flow velocities.For the BCC configuration,some differences can be observed in the pore jet flow structure between the simulations and the experiments,but the general flow velocity distribution shows a good overall agreement.The axial velocity is generally higher for the pores located near the centre of the packed bed than for the pores near the wall.In addition,the axial velocities are observed to increase near the peripheral pores of the packed bed.This behaviour is predominant for the BCC configuration as compared to the SUC configuration.The velocities near the peripheral pores can become even higher than those at the central pores for the BCC configuration.It is shown that both the experiments as well as the simulations can be used to study the complex fluid structures inside a packed bed reactor.
文摘The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compaction index, denoted by a, b, c, and K, respectively） may be classified into the 2-parameter model （with a and b incorporated）, the compressible model （with a, b, and 1（incorporated）, and the 3- parameter model （with a, b, and c incorporated）. This paper evaluates these models by comparing their respective packing density predictions with the test results published in the literature. It was found that their accuracy varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, some of them become inaccurate and the errors tend to be larger at around the volumetric fractions giving maximum packing density. Relatively, the 3-parameter model is the most accurate and widely applicable.
基金supported by National Natural Science Foundation of China(Nos.51806085,51676089)China Postdoctoral Science Foundation(2018M642175)the Double Innovation Talents of Jiangsu Province and Jiangsu University Youth Talent Cultivation Program Funded Project
文摘Packed-bed reactors(PBRs)hold great promise for environmental applications,but a deeper understanding of the behavior of plasma discharge within PBRs is required.To this end,a partial-discharge alternative equivalent circuit for PBRs was established in this work.Dielectric particles(glass beads or glass sand)were used to place focus on the effects of the particle size and shape on the partial discharge behavior of the oxygen PBRs.Some electrical characterizations were explored(e.g.the effective dielectric capacitance,partial discharge coefficient,and corrected burning voltage)that may differ from long-standing interpretations.The findings indicate that the suppressive effect of surface discharge on filament discharge is stronger with the decrease of the particle size.For partial discharge,the effective dielectric capacitance is always less than the dielectric capacitance.The corrected burning voltage and partial discharge tendency increase with the decrease of the particle size.As compared to an empty reactor,the average electric field in the PBR was found to be improved by 3–4 times,and the ozone energy efficiency and production were promoted by more than 20%and 15%,respectively.The plasma processing capacity can therefore be improved by choosing a relatively large size or a complex,irregularly-shaped packing material that is suitable for the discharge gap.
基金Projects(50934002,51074013,51304076,51104100)supported by the National Natural Science Foundation of ChinaProject(IRT0950)supported by the Program for Changjiang Scholars Innovative Research Team in Universities,ChinaProject(2012M510007)supported by China Postdoctoral Science Foundation
文摘Methods and procedures of three-dimensional （3D） characterization of the pore structure features in the packed ore particle bed are focused. X-ray computed tomography was applied to deriving the cross-sectional images of specimens with single particle size of 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 ram. Based on the in-house developed 3D image analysis programs using Matlab, the volume porosity, pore size distribution and degree of connectivity were calculated and analyzed in detail. The results indicate that the volume porosity, the mean diameter of pores and the effective pore size （d50） increase with the increasing of particle size. Lognormal distribution or Gauss distribution is mostly suitable to model the pore size distribution. The degree of connectivity investigated on the basis of cluster-labeling algorithm also increases with increasing the particle size approximately.
文摘The vanadium-titanium magnetite concentrate from Panxi region of China was pretreated by high pressure roller grinding（ HPRG） and then used in pelletization. Size distribution change of the vanadiumtitanium magnetite concentrate after HPRG and the improvement of its green pellet strength were investigated. The results indicated that,besides the increase of fine particles,the vanadium-titanium magnetite concentrate after HPRG had a smaller size ratio of fine particle to coarse particle of 0. 126,meaning a lower porosity,compared with the size ratio of raw material of 0. 157. The concentrate particles were more closely packed when there was a smaller size ratio of fine particle to coarse particle. The particle packing in the green pellets was closer after HPRG,which strengthened the green pellets with an average drop number of 5. 1（ drop height of 0. 5 m） and average compressive strength of 13. 1 N per pellet of 11 mm in diameter.
基金supported by the National Natural Science Foundation of China(No.50974040)the Fundamental Research Funds for the Central Universities(No.N100402009)
文摘Two packing structures with the maximum packing densities of 0.64 and 0.74 for the amorphous state and crystalline state, respectively, were numerically reproduced in the packing densification of equal spheres subjected to one- dimensional and three-dimensional vibrations using the discrete element method （DEM）, and the results were physically validated. These two packing structures were analyzed in terms of coordination number （CN）, radial distribution function （RDF）, angular distribution function （ADF）, and pore size distribution （Voronoi/Delaunay tessellation）. It is shown that CN distributions have the peak values of 7 and 12 for the amorphous state and crystalline state, respectively. RDF and ADF distributions show isolated peaks and orientation preferences for the crystalline state, indicating the long range and angle correlation among particles commonly observed in the crystalline state. Voronoi/Delaunay tessellation also shows smaller and narrower pore size distribution for the crystalline state.
基金supported by the National Science Foundation of the United States under a research grant (CMMI-1917238)
文摘Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.
基金partially supported through a MURI from the United States Office of Naval Research
文摘Particle based models of composite anodes are useful tools for exploring the behavior of SOFC systems. As part of our efforts to develop models for understanding fuel cells, we have been building models of Ni-YSZ composite anodes using experimentally measured particle size distributions. The objectives of this study were to characterize the percolation threshold and conductivity of these models in comparison to simpler mono dispersed and biphasic particle size distributions from the literature. We found that the average values for the onset of percolation and the measured conductivity of the models with experimentally measured particle size distributions are similar to those for the simple distributions and the experimentally measured distributions. For all of the configurations evaluated, the onset of percolation in the Nickel phase occurred at a solid fraction of Nickel between 20% and 25%. This corresponded almost exactly to the point at which the coordination number between Nickel phase particles reached 2.2. The significant finding was that the variation in the value for the conductivity, as measured by the standard deviation of the results, was several orders of magnitude higher than for the simpler systems. We explored the validity of our assumptions, specifically the assumption of random particle placement, by building a particle model directly from FIB-SEM data. In this reconstruction, it was clear that the location of particles was not random. Particles of the same type and size had much likelihood of contact higher than would indicated by random location.
基金The first author gratefully acknowledges the Ministry of Research,Technology,and Higher Education(KEMENRISTEKDIKTI)of Republic Indonesia for the scholarship funding through the Research and Innovation in Science and Technology Project(RISET-Pro)program and also the University of Glasgow for supporting this research.
文摘In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.
基金the National Natural Science Foundation of China(grant No.51374070)Liaoning Revitalization Talents Program(grant No.XLYC1805007)of ChinaNatural Science Foundation of Jiangsu Province(grant No.BK20200269)for the financial support to this work.
文摘Metastability,disorder and jamming are the typical characteristics of amorphous systems,while the related structure changes remain unclear.Sphere packing is often used as a structure model for amorphous and crystalline states.In this article,sphere packing systems with packing densities ranging from 0.50 to 0.74 were simulated by using Discrete Element Method(DEM),and the obtained packing structures were assessed to investigate the densification process and jamming properties.An order parameter that can effectively distinguish the order and disorder of packing structures was proposed based on the distribution characteristics of jamming angles.Then the evolution of jamming characteristics during the transition from Random Loose Packing(RLP)to Random Close Packing(RCP)and the jamming-jamming relations of different packing structures were demonstrated.On this basis,a correlation between order-jamming-metastable states from the microscopic structural perspective was established,which is of valuable theoretical and practical implications for the characterization and synthesis of crystalline and amorphous materials.
基金supported by the Science and Technology Project of State Grid Corporation of China(Grant No.5400-202419199A-1-1-ZN)。
文摘The particle packed bed energy storage system has advantages such as low costs and wide temperature ranges,which can be combined with solar thermal power generation systems to solve the inherent volatility and discontinuity of renewable energy.Developing new materials with low costs and excellent storage performances is one of the eternal research hotspots in the field of energy storage.This paper innovatively uses sintered ore particles as energy storage material and studies the effect of particle size on the airflow resistance characteristics,energy storage characteristics,and thermocline evolution characteristics of the packed bed through thermal energy storage experiments.The results indicate that for the particles in the macro scale,the smaller the particle,the lower the absolute permeability of the bed and the greater the airflow resistance.The packed bed with smaller particles has a larger specific surface area,larger bulk mass,and smaller bed voidage.Therefore,the packed beds with smaller particles have better thermocline characteristics,less irreversible loss,and can achieve higher thermal efficiency and higher exergy efficiency in the heat storage cycle.The cycle thermal efficiency in packed beds with 25-40 mm,16-25 mm,and 10-16 mm particles is 53.58%,56.27%,and 57.60%,respectively,and the cycle exergy efficiency is 61.81%,69.25%,and 74.13%,respectively.Moreover,this paper also studies the effect of discharging airflow rates on thermal storage performance.The experimental results indicate that suitable discharging strategies should be selected based on different heat demands.
基金This work was supported by the Fundamental Research Funds for the Central Universities(grant No.2022ZFJH04)。
文摘Solid particles instead of molten salt as a heat storage medium for extracted steam energy storage are essential in thermal power flexibility retrofit. This study constructs a charge-discharge experimental device using by-products from the steel industry as heat storage materials, similar to a battery cell, which is easily scalable and accomplishes the steam-solid particle-steam energy conversion. Investigation parameters include temperature distribution, power variation, and cycle efficiency for different charging and discharging modes. Results indicate that the charging mode II outperforms mode I in temperature uniformity, charging flow rate, and pressure loss, yielding higher charging power and total convective heat transfer coefficients at 13 kW and 275 W/(m^(2) K), respectively. The pilot device demonstrates commendable insulating properties. Its heat dissipation rate is approximately 33.33%, which surpasses that of reported thermal storage devices. Moreover, the mode II exhibits superior temperature non-uniformity during heat release, ensuring that 40 kg/h of superheated steam at 220 ℃ can be produced continuously for 5 min. The cycling efficiency is noteworthy, reaching 65% in low flow rate discharge, accompanied by 79% charging efficiency and 82% discharging efficiency. A temperature difference cloud map elucidates the primary phase change region, emphasizing preheating, evaporation, and superheating segments. Experimental results provide new ideas for combining waste elimination in the steel industry and energy storage in thermal power plants.
基金financially supported by the National Science&Technology Pillar Program of China(Grant No.2015AA042502)
文摘Coated sands are used extensively for additive manufacturing sand molds in the metal casting process, and the packing structure changes caused by the resin flow promote the shrinkage and deformation of the part. During the coated sand heating, the resin on the surface flowing to the contact points of the particles forms the resin neck and causes particles to pack close to each other. In this work, the diameters of the coated ceramsite sand before and after heating were measured based on in-situ experimental observations with image measuring apparatus and blue laser, to obtain the relationship between resin coating thickness and the particle diameter. The particle packing model was established to describe the particles＇ achievement of a stable state one by one. A re-packing simulation was then performed after reducing the particle diameter according to the resin coating thickness, to obtain the shrinkage ratios at different particle size distributions. It was found that the resin coating thickness increased from 0.8 to 2.3 IJm as the particle diameter increased from 107 to 500 IJm, for the coated ceramsite sand with the resin content of 2wt.%; the shrinkage ratio decreased first and then increased as the particle diameter increased. The experimental minimum shrinkage ratio was 3.28%, and the corresponding particle diameter was 300-375 IJm, while the minimum shrinkage ratio obtained by simulation was 3.43%, and the corresponding particle diameter was 214-300 IJm. After mixing the five groups proportionally, the shrinkage ratios of the simulation and experiment dropped to 2.81% and 3.04%, respectively, indicating the best results.
基金supported by National Natural Science Foundation of China (No. 51806085)China Postdoctoral Science Foundation (No. 2018M642175)+2 种基金Jiangsu Planned Projects for Postdoctoral Research Fund (No. 2018K101C)Open Research Subject of Key Laboratory of Automotive Measurement, Control and Safety (Xihua University) (No. QCCK2021-007)the Graduate Student Innovation Fund Project of Jiangsu Province (No. KYCX21_3354)
文摘To compensate for the shortcomings of the thermal and catalytic regeneration of the diesel particulate filter(DPF),a self-designed packed-bed dielectric barrier discharge(DBD)reactor for DPF regeneration was developed.The DBD reactor with the main active substance of nonthermal plasma(NTP)as the target parameter was optimized by adjusting the feed gas,packing particles(material or size),and cooling water temperature.Moreover,a set of optimal working parameters(gas source,O_2;packing particles,1.2–1.4 mm ZrO_(2);and cooling water temperature,20℃)was selected to evaluate the effect of different O_(3) concentrations on DPF regeneration.The research results showed that selecting packing particles with high dielectric constant and large particles,as well as reducing the cooling water temperature,with oxygen as the feed gas,contributed to an increase in O_(3) concentration.During DPF regeneration,the following changes were observed:the power of the NTP reactor decreased to lower than 100 W,the O_(3) concentration increased from 15 g m^(-3) to 45 g m^(-3),the CO and CO_2 volume fractions of the particulate matter decomposition products increased,and the peak regeneration temperature increased to 173.4℃.The peak temperature arrival time was 60 min earlier,indicating that the regeneration rate of DPF increased with the increase in O_(3) concentration.However,the O_(3) utilization rate(the amount of carbon deposit removed per unit volume O_(3))initially increased and then decreased;when the O_(3) concentration was set to 25 g m^(-3),the highest O_(3) utilization rate was reached.The packed-bed DBD technology contributed to the increase in the concentration of NTP active substances and the regeneration efficiency of DPF.It provides a theoretical and experimental basis for high-efficiency regeneration of DPF at low temperatures(<200℃).
基金We are grateful to the financial support of National Natural Science Foundation of China （No. 51374070） and Fundamental Research Funds for the Central Universities of China （N120202001, N130102001）.
文摘Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration time, frequency, amplitude, vibration strength, container size, and the aspect ratio and spheric- ity of the particle on the packing density were analyzed and discussed. For each initial packing density with a certain aspect ratio, operating parameters were optimized to achieve much denser packing. The results indicate that the packing density initially increases with vibration time and then remains con- stant. The effects of vibration frequency and amplitude on the packing densification have similar trends, i.e. the packing density first increases with the vibration frequency or amplitude to a high value and then decreases; too large or small frequency or amplitude does not enhance densification. Increasing the container size can reduce container wall effects and help achieve a high packing density. Varying the particle aspect ratio and sphericity can lead to different dense random packing structures. Overall, based on results of the examined systems, the highest random packing density obtained in an infinite sized container can reach 0.73, which agrees well with corresponding numerical and analytical results in the literature.
基金supported by National Natural Science Foundation of China(No.50974040)Personnel Department of Liaoning Province(No.2009921053)
文摘Densification of mono-sized sphere packings using two-dimensional （2D） vibration was experimentally studied. The effects of vibration mode, amplitude and frequency, feeding method, and container size on packing density were systematically analyzed. Useful results were obtained.
文摘The packing densification of binary spherical mixtures under 3D mechanical vibration was studied experimentally. The influences of vibration frequency （ω）, volume fraction of large spheres （XL）, sphere size ratio （r, diameter ratio of small to large spheres）, and container size （D） on the random binary packing density （p） were systematically analyzed. For any given set of conditions, there exist optimal ω and XL to realize the densest random binary packing; too large or small ω and XL is not helpful for densification. The influences of both r and D on p are monotonic; either reducing r or increasing D leads to a high value of p. With all other parameters held constant, the densest random packing occurs when XL is dominant, which is in good agreement with the Furnas relation. Moreover, the highest random binary packing density obtained in our work agrees well with corresponding numerical and analytical results in the literature.
基金the support of this research by the National Science and Technology Major Project(grant No.2011ZX06901-003)the National Natural Science Foundation of China(grant No.51576211)+1 种基金the National High Technology Research and Development Program of China(863)(grant No.2014AA052701)the funds of Nuclear Power Technology Innovation Centre(grant Nos.HDLCXZX-2020-HD-022 and HDLCXZX-2021-ZH-024).
文摘The motion and deformation of soft particles are commonly encountered and important in many appli-cations.A discrete element-embedded finite element model(DEFEM)is proposed to solve soft particle motion and deformation,which combines discrete element and finite element methods.The collisional surface of soft particles is covered by several dynamical embedded discrete elements(EDEs)to model the collisional external forces of the particles.The particle deformation,motion,and rotation are inde-pendent of each other in the DEFEM.The deformation and internal forces are simulated using the finite element model,whereas the particle rotation and motion calculations are based on the discrete element model.By inheriting the advantages of existing coupling methods,the contact force and contact search between soft particles are improved with the aid of the EDE.Soft particle packing is simulated using the DEFEM for two cases:particle accumulation along a rectangular straight wall and a wall with an inclined angle.The large particle deformation in the lower layers can be simulated using current meth-ods,where the deformed particle shape is either irregular in the marginal region or nearly hexagonal in the tightly packed central region.This method can also be used to simulate the deformation,motion,and heat transfer of non-spherical soft particles.
