In this paper,a novel method for investigating the particle-crushing behavior of breeding particles in a fusion blanket is proposed.The fractal theory and Weibull distribution are combined to establish a theoretical m...In this paper,a novel method for investigating the particle-crushing behavior of breeding particles in a fusion blanket is proposed.The fractal theory and Weibull distribution are combined to establish a theoretical model,and its validity was verified using a simple impact test.A crushable discrete element method(DEM)framework is built based on the previously established theoretical model.The tensile strength,which considers the fractal theory,size effect,and Weibull variation,was assigned to each generated particle.The assigned strength is then used for crush detection by comparing it with its maximum tensile stress.Mass conservation is ensured by inserting a series of sub-particles whose total mass was equal to the quality loss.Based on the crushable DEM framework,a numerical simulation of the crushing behavior of a pebble bed with hollow cylindrical geometry under a uniaxial compression test was performed.The results of this investigation showed that the particle withstands the external load by contact and sliding at the beginning of the compression process,and the results confirmed that crushing can be considered an important method of resisting the increasing external load.A relatively regular particle arrangement aids in resisting the load and reduces the occurrence of particle crushing.However,a limit exists to the promotion of resistance.When the strain increases beyond this limit,the distribution of the crushing position tends to be isotropic over the entire pebble bed.The theoretical model and crushable DEM framework provide a new method for exploring the pebble bed in a fusion reactor,considering particle crushing.展开更多
The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The th...The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5models are modified to take the cyclic operation of the circulator, heat, exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases.展开更多
As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within trit...As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within tritium-breeding pebble beds are subjected to prolonged neutron irradiation,high thermal loads,and strong magnetic fields in fusion environments.Such conditions render them susceptible to pulverization and fragmentation.The resulting fragments and powders migrate and are deposited into the gas channel,driven by the purge gas.The reduction in the effective flow area of the gas increases the flow resistance,resulting in tritium retention,degraded heat transfer,and other adverse effects.These conditions impair the thermodynamic properties of the pebble beds and hinder the self-maintenance of tritium.Limited information exists on powder migration and clogging mechanisms in fusion blanket pebble beds,particularly under diverse physical conditions.The aim of this study was to use a computational fluid dynamics model coupled with the discrete element method(CFD-DEM)to numerically explore powder migration and clogging in pebble beds.The model considers factors such as breeder orientation,purge velocity,powder size distribution,and friction coefficient.We propose two migration and clogging mechanisms.One involves powder with a large particle size,and the other does not.The results indicate that the powder migration velocity progresses through three stages:rapid decay,linear decay,and stability.Pebble-bed clogging manifests in two forms:extensive superficial clogging and uniform internal clogging.Two fitted curves were used to depict the migration and clogging tendencies.The powder size distribution significantly influenced the powder migration.The breeder orientation,powder size,and friction coefficient affected the distribution of the clogging powders.However,the impact of the purge velocity on powder migration and clogging in pebble beds was limited,and this effect varied significantly with different particle size ratios.Based on the analysis,a formula is proposed to characterize the behavior of the powder in the pebble beds.The results of this study can aid in analyzing and predicting powder dynamics in pebble beds.展开更多
The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method.Sev...The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method.Several important static packing characteristics under different coefficients of friction and restitution are presented and discussed.The results show that the coefficients of friction and restitution impose opposite effects on the packing heights and global packing factor.Neither the coefficient of friction nor restitution affected the oscillation width of the wall,whereas their effects are primarily reflected in the oscillation amplitude of the radial local packing factor and the axial local packing factor distribution at the top of the pebble bed.In both the contact force distribution and coordination number distribution,a left-shifted phenomenon appearing as the coefficient of friction occurred,and only the magnitude of the maximum frequency is affected when the coefficient of restitution changed from 0.1 to 0.9.In all simulation cases,the effects of the coefficients of friction and restitution are similar to that of cross-impact.展开更多
This paper presents the study of the dynamic characteristics of confined mixed pebble beds with different friction under different vibration conditions using the discrete element method.Theλsegre-gation index is used...This paper presents the study of the dynamic characteristics of confined mixed pebble beds with different friction under different vibration conditions using the discrete element method.Theλsegre-gation index is used to quantify the degree of particle mixing or segregation.The percolation,convection and diffusion mechanisms are responsible for the segregation patterns of the mixed pebble.The results show the degree of segregation can be suppressed by decreasing the vibration acceleration or free space height below a threshold.Further simulation reveals the threshold of vibration acceleration or free space height both are related to the bed height increment which determines the strength of the percolation mechanism.In addition,the strength of percolation and convection becomes weaker by decreasing the friction of particles and walls,which makes the pebbled bed remains in a mixed state under vibration.These findings are significant to clarify the main factors behind the three segregation mechanisms and hence provide solutions to retaining the mixed state of the Li2TiO3&Be12Ti mixed pebble bed.展开更多
A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phaseflow.These processes have been studied in plunging jets,dropshafts,and hydraulic jumps on a smooth bed....A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phaseflow.These processes have been studied in plunging jets,dropshafts,and hydraulic jumps on a smooth bed.As a first attempt,this study examined the bubble clustering process in hydraulic jumps on a pebbled rough bed using experimental data for 1.70<Fr_(1)<2.84(with Fr_(1) denoting the inflow Froude number).The basic properties of particle grouping and clustering,including the number of clusters,the dimensionless number of clusters per second,the percentage of clustered bubbles,and the number of bubbles per cluster,were analyzed based on two criteria.For both criteria,the maximum cluster count rate was greater on the rough bed than on the smooth bed,suggesting greater interactions between turbulence and bubbly flow on the rough bed.The results were consistent with the longitudinal distribution of the interfacial velocity using one of the criteria.In addition,the clustering process was analyzed using a different approach:the interparticle arrival time of bubbles.The comparison showed that the bubbly flow structure had a greater density of bubbles per unitflux on the rough bed than on the smooth bed.Bed roughness was the dominant parameter close to the jump toe.Further downstream,Fr_(1) predominated.Thus,the rate of bubble density decreased more rapidly for the hydraulic jump with the lowest Fr_(1).展开更多
This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time ...This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.展开更多
Bed Load Motion and its transport rate is one of the basic issues in river dynamics.In this paper,the authors discussed the stochastic nature of bed load motion in Chuanjiang River in details.Chungjiang liesin the ups...Bed Load Motion and its transport rate is one of the basic issues in river dynamics.In this paper,the authors discussed the stochastic nature of bed load motion in Chuanjiang River in details.Chungjiang liesin the upstream reach of Yangtze River.Its stochastic nature is shown in the following four aspects.Firstly,even though all the conditions are the same,due to the fluctuation of the flow,the bed load discharge and thelocation and width of sediment transport belts are different.Secondly,during the process of bed load motion,pebbles show the strong nature of intermittence.Thirdly,the sediment discharges through upstream and down-stream reach are not equal,i.e.the pebble motion exists the discontinuity.Fourthly,annual mean transportrates of bed load for different stations are different and variation of transport rate of pebbles for a given stationwith year is large.The four aspects will be discussed one by one detailedly.展开更多
Xihe Bridge is located in Qionglai, Chengdu. Chengdu Plain is an alluvial plain in the central and western Sichuan Basin. It is the largest plain in southwest China and one of the areas with dense river networks. The ...Xihe Bridge is located in Qionglai, Chengdu. Chengdu Plain is an alluvial plain in the central and western Sichuan Basin. It is the largest plain in southwest China and one of the areas with dense river networks. The surface of the plain is loose, and the sediments are very thick. The geological structure is that a thick layer of gravel soil is covered on hard rocks. Relying on the renovation project of Xihe Bridge, the renovation project of Xihe Bridge is a highway project, which consists of a 240m(8x30m) prefabricated box girder simply supported bridge, 36 rotary bored pile foundations, with a designed pile length of 30m and a pile+column structure as the substructure. According to the characteristics of pile foundation construction in Xihe River, the rotary drilling rig is adopted, and yellow clay is used as the wall protection material and the construction technology of double liners, which passes through the water-rich pebble layer and then the pile foundation is bored. Considering the cost-effectiveness, green construction and other factors, this paper studies the application of rotary bored pile in pore-forming technology in water-rich pebble bed.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
The P1 approximation is a computationally efficient model for thermal radiation.Here,we present a P1 formulation in the context of the combined computational fluid dynamics and discrete element method(CFD-DEM),includi...The P1 approximation is a computationally efficient model for thermal radiation.Here,we present a P1 formulation in the context of the combined computational fluid dynamics and discrete element method(CFD-DEM),including closures for dependent scattering and coarse-graining.Using available analytical and semi-analytical solutions,we find agreement for steady-state and transient quantities in sizedisperse systems.Heat flux is identified as the most sensitive quantity to predict,displaying unphysical spatial oscillations.These oscillations are due to a temperature slip at the locations of abrupt change in solid fraction.We propose two techniques that mitigate this effect:smoothing of the radiative properties,and pseudo-scattering.Furthermore,using up to a million times enlarged particles,we demonstrate practically limitless compatibility with coarse-graining.Finally,we compare predictions made with our code to experimental data for a pebble bed under vacuum conditions,and in presence of nitrogen.We find that a carefully calibrated simulation can replicate trends observed in experiments,with relative temperature error of less than 10%.展开更多
基金supported by Anhui Provincial Natural Science Foundation(2408085QA030)Natural Science Research Project of Anhui Educational Committee,China(2022AH050825)+3 种基金Medical Special Cultivation Project of Anhui University of Science and Technology(YZ2023H2C008)the Excellent Research and Innovation Team of Anhui Province,China(2022AH010052)the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology,China(2021yjrc51)Collaborative Innovation Program of Hefei Science Center,CAS,China(2019HSC-CIP006).
文摘In this paper,a novel method for investigating the particle-crushing behavior of breeding particles in a fusion blanket is proposed.The fractal theory and Weibull distribution are combined to establish a theoretical model,and its validity was verified using a simple impact test.A crushable discrete element method(DEM)framework is built based on the previously established theoretical model.The tensile strength,which considers the fractal theory,size effect,and Weibull variation,was assigned to each generated particle.The assigned strength is then used for crush detection by comparing it with its maximum tensile stress.Mass conservation is ensured by inserting a series of sub-particles whose total mass was equal to the quality loss.Based on the crushable DEM framework,a numerical simulation of the crushing behavior of a pebble bed with hollow cylindrical geometry under a uniaxial compression test was performed.The results of this investigation showed that the particle withstands the external load by contact and sliding at the beginning of the compression process,and the results confirmed that crushing can be considered an important method of resisting the increasing external load.A relatively regular particle arrangement aids in resisting the load and reduces the occurrence of particle crushing.However,a limit exists to the promotion of resistance.When the strain increases beyond this limit,the distribution of the crushing position tends to be isotropic over the entire pebble bed.The theoretical model and crushable DEM framework provide a new method for exploring the pebble bed in a fusion reactor,considering particle crushing.
基金The project supported by European Fusion Development Agreement (EFDA) Technology Work Program
文摘The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5models are modified to take the cyclic operation of the circulator, heat, exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases.
文摘As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within tritium-breeding pebble beds are subjected to prolonged neutron irradiation,high thermal loads,and strong magnetic fields in fusion environments.Such conditions render them susceptible to pulverization and fragmentation.The resulting fragments and powders migrate and are deposited into the gas channel,driven by the purge gas.The reduction in the effective flow area of the gas increases the flow resistance,resulting in tritium retention,degraded heat transfer,and other adverse effects.These conditions impair the thermodynamic properties of the pebble beds and hinder the self-maintenance of tritium.Limited information exists on powder migration and clogging mechanisms in fusion blanket pebble beds,particularly under diverse physical conditions.The aim of this study was to use a computational fluid dynamics model coupled with the discrete element method(CFD-DEM)to numerically explore powder migration and clogging in pebble beds.The model considers factors such as breeder orientation,purge velocity,powder size distribution,and friction coefficient.We propose two migration and clogging mechanisms.One involves powder with a large particle size,and the other does not.The results indicate that the powder migration velocity progresses through three stages:rapid decay,linear decay,and stability.Pebble-bed clogging manifests in two forms:extensive superficial clogging and uniform internal clogging.Two fitted curves were used to depict the migration and clogging tendencies.The powder size distribution significantly influenced the powder migration.The breeder orientation,powder size,and friction coefficient affected the distribution of the clogging powders.However,the impact of the purge velocity on powder migration and clogging in pebble beds was limited,and this effect varied significantly with different particle size ratios.Based on the analysis,a formula is proposed to characterize the behavior of the powder in the pebble beds.The results of this study can aid in analyzing and predicting powder dynamics in pebble beds.
基金This study was supported by the Collaborative Innovation Program of Hefei Science Center,Chinese Academy of Sciences,under grant number 2019HSC-CIP006.
文摘The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method.Several important static packing characteristics under different coefficients of friction and restitution are presented and discussed.The results show that the coefficients of friction and restitution impose opposite effects on the packing heights and global packing factor.Neither the coefficient of friction nor restitution affected the oscillation width of the wall,whereas their effects are primarily reflected in the oscillation amplitude of the radial local packing factor and the axial local packing factor distribution at the top of the pebble bed.In both the contact force distribution and coordination number distribution,a left-shifted phenomenon appearing as the coefficient of friction occurred,and only the magnitude of the maximum frequency is affected when the coefficient of restitution changed from 0.1 to 0.9.In all simulation cases,the effects of the coefficients of friction and restitution are similar to that of cross-impact.
基金the financial support of the National MCF Energy R&D Program(No.2019YFE03130001)the Comprehensive Research Facility for Fusion Technology(CRAFT)Program of China(Contract No.2018-000052-73-01-001228)+1 种基金the National Natural Science Foundation of China(No.12105315&12205330)the Science Foundation of ASIPP(No.DSJ-2021-05).
文摘This paper presents the study of the dynamic characteristics of confined mixed pebble beds with different friction under different vibration conditions using the discrete element method.Theλsegre-gation index is used to quantify the degree of particle mixing or segregation.The percolation,convection and diffusion mechanisms are responsible for the segregation patterns of the mixed pebble.The results show the degree of segregation can be suppressed by decreasing the vibration acceleration or free space height below a threshold.Further simulation reveals the threshold of vibration acceleration or free space height both are related to the bed height increment which determines the strength of the percolation mechanism.In addition,the strength of percolation and convection becomes weaker by decreasing the friction of particles and walls,which makes the pebbled bed remains in a mixed state under vibration.These findings are significant to clarify the main factors behind the three segregation mechanisms and hence provide solutions to retaining the mixed state of the Li2TiO3&Be12Ti mixed pebble bed.
文摘A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phaseflow.These processes have been studied in plunging jets,dropshafts,and hydraulic jumps on a smooth bed.As a first attempt,this study examined the bubble clustering process in hydraulic jumps on a pebbled rough bed using experimental data for 1.70<Fr_(1)<2.84(with Fr_(1) denoting the inflow Froude number).The basic properties of particle grouping and clustering,including the number of clusters,the dimensionless number of clusters per second,the percentage of clustered bubbles,and the number of bubbles per cluster,were analyzed based on two criteria.For both criteria,the maximum cluster count rate was greater on the rough bed than on the smooth bed,suggesting greater interactions between turbulence and bubbly flow on the rough bed.The results were consistent with the longitudinal distribution of the interfacial velocity using one of the criteria.In addition,the clustering process was analyzed using a different approach:the interparticle arrival time of bubbles.The comparison showed that the bubbly flow structure had a greater density of bubbles per unitflux on the rough bed than on the smooth bed.Bed roughness was the dominant parameter close to the jump toe.Further downstream,Fr_(1) predominated.Thus,the rate of bubble density decreased more rapidly for the hydraulic jump with the lowest Fr_(1).
文摘This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.
基金Supported by National Key Basic Besearch and Development Program of(973 Program)(2003CB415202)Key Project of Chinese Ministry of China(03134)
文摘Bed Load Motion and its transport rate is one of the basic issues in river dynamics.In this paper,the authors discussed the stochastic nature of bed load motion in Chuanjiang River in details.Chungjiang liesin the upstream reach of Yangtze River.Its stochastic nature is shown in the following four aspects.Firstly,even though all the conditions are the same,due to the fluctuation of the flow,the bed load discharge and thelocation and width of sediment transport belts are different.Secondly,during the process of bed load motion,pebbles show the strong nature of intermittence.Thirdly,the sediment discharges through upstream and down-stream reach are not equal,i.e.the pebble motion exists the discontinuity.Fourthly,annual mean transportrates of bed load for different stations are different and variation of transport rate of pebbles for a given stationwith year is large.The four aspects will be discussed one by one detailedly.
文摘Xihe Bridge is located in Qionglai, Chengdu. Chengdu Plain is an alluvial plain in the central and western Sichuan Basin. It is the largest plain in southwest China and one of the areas with dense river networks. The surface of the plain is loose, and the sediments are very thick. The geological structure is that a thick layer of gravel soil is covered on hard rocks. Relying on the renovation project of Xihe Bridge, the renovation project of Xihe Bridge is a highway project, which consists of a 240m(8x30m) prefabricated box girder simply supported bridge, 36 rotary bored pile foundations, with a designed pile length of 30m and a pile+column structure as the substructure. According to the characteristics of pile foundation construction in Xihe River, the rotary drilling rig is adopted, and yellow clay is used as the wall protection material and the construction technology of double liners, which passes through the water-rich pebble layer and then the pile foundation is bored. Considering the cost-effectiveness, green construction and other factors, this paper studies the application of rotary bored pile in pore-forming technology in water-rich pebble bed.
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.
基金funded through Marie SKEODOWSKA-CURIE Innovative Training Network MATHEGRAM,the People Programme(Marie SKLODOWSKA-CURIE Actions)of the European Union's Horizon 2020 Programme H2020 under REA grant agreement No.813202.
文摘The P1 approximation is a computationally efficient model for thermal radiation.Here,we present a P1 formulation in the context of the combined computational fluid dynamics and discrete element method(CFD-DEM),including closures for dependent scattering and coarse-graining.Using available analytical and semi-analytical solutions,we find agreement for steady-state and transient quantities in sizedisperse systems.Heat flux is identified as the most sensitive quantity to predict,displaying unphysical spatial oscillations.These oscillations are due to a temperature slip at the locations of abrupt change in solid fraction.We propose two techniques that mitigate this effect:smoothing of the radiative properties,and pseudo-scattering.Furthermore,using up to a million times enlarged particles,we demonstrate practically limitless compatibility with coarse-graining.Finally,we compare predictions made with our code to experimental data for a pebble bed under vacuum conditions,and in presence of nitrogen.We find that a carefully calibrated simulation can replicate trends observed in experiments,with relative temperature error of less than 10%.
