Powder flow behaviour is the result of countless combinations of interparticle forces of different natures: frictional,interlocking,cohesive and adhesive forces.We identify the rheological tests where one mechanism is...Powder flow behaviour is the result of countless combinations of interparticle forces of different natures: frictional,interlocking,cohesive and adhesive forces.We identify the rheological tests where one mechanism is most likely to dominate over the rest,and we propose the best descriptors of uniquely cohesive or frictional effects.We describe the procedure for a fluidisation test and the features of the results linked to powder cohesivity.We contrast these features against shear test results to determine powder frictional properties,explaining the conditions and limitations of the analysis.We use solid volume fraction and compressibility measurements to assess the extent to which the different mechanisms influence natural packing and forced flow in intermediate stress regimes.The proposed experimental protocol and framework of interpretation is applied to a wide range of powdered materials,representing typical industrial issues.The qualities of the characterisation are discussed and compared to those associated with traditional rheological testing methods.The framework successfully differentiates the effects of the various interparticle interaction mechanisms on powder flow,enabling a comprehensive prediction of powder behaviour in a variety of handling and processing settings.The metrics used are all normalised,allowing for a universal direct comparison of flowability across completely different materials.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
In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci poi...In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the ]enike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.展开更多
The use of single and twin-screw extruders for solid-phase reactions is a promising method to intensify a process in a more sustainable manner.In this manuscript,we report a detailed analysis of the residence time dis...The use of single and twin-screw extruders for solid-phase reactions is a promising method to intensify a process in a more sustainable manner.In this manuscript,we report a detailed analysis of the residence time distribution(RTD)in vertical single-screw reactors.The results will help in the selection of the right screw design that would help achieve the desired residence time,which is necessary for a reaction to happen.Experiments were conducted in three vertical screw reactors(having fixed shaft diameter)with varying dimensions using granular free-flowing powders of sodium chloride and silica with a mean particle size of∼25μm.RTD behavior was modeled using the radial particle velocities in the screw reactor's centrifugal field.Further,a method is proposed for estimating the axial dispersion coefficient of dry powders in such sheared flows using true and bulk densities of the powder and the screw shear rate.This dispersion coefficient is used in the axially dispersed plug flow model to describe the RTD behavior of screw reactors with acceptable accuracy.The theoretically predicted and experimentally obtained dispersion coefficients are found to be similar thereby confirming the suitability of the model.展开更多
To investigate the hot deformation behavior of powder-forged （P/F） Fe-0. 5C：-2Cu steel, the hot compres- sion tests were conducted at temperatures ranging from 900 to 1000 ℃ and strain rates from 0.1 to 10 s-1 usi...To investigate the hot deformation behavior of powder-forged （P/F） Fe-0. 5C：-2Cu steel, the hot compres- sion tests were conducted at temperatures ranging from 900 to 1000 ℃ and strain rates from 0.1 to 10 s-1 using Gleeble-1500 thermal simulator. The true stress-true strain curves at different temperatures and strain rates of P/F steel were obtained. It is found that dynamic recovery only occurs as strain rate is 10 s 1 at 900 ℃, and the dynamic recrystallization is the main softening mechanism. The flow stress increases with decreasing temperature and increas- ing strain rate. The experimental data are employed to develop constitutive equations on the basis of the Arrhenius- type equation by introducing the strain with nonlinear fitting. The flow stresses prediel：ed by the proposed constitu- tive equations are in good agreement with the experimental values, and the correlation coefficient （R2） and the aver- age absolute relative error （AARE） are 0. 995 25 and 3.07% respectively. These results indicate the proposed consti- tutive equations can effectively describe the hot deformation behavior of the material.展开更多
A screw powder feeder is an important device for industrial applications. There are many parameters which affect the performance of the screw powder feeder, such as the shapes of the helical screw impeller, the number...A screw powder feeder is an important device for industrial applications. There are many parameters which affect the performance of the screw powder feeder, such as the shapes of the helical screw impeller, the number of screw pitches, etc. This paper presents an analysis of a gas-solid two-phase through screw powder feeder by using a commercial Computational Fluid Dynamics（CFD） code, Fluent. The K-ε model is used to simulate gas flow. Particle trajectory is obtained by the use of a discrete phase model. The results show the effects of gas velocity and panicle size on the transportation performance.展开更多
To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study th...To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.展开更多
The hot deformation behavior of powder met- allurgical （PM） TiAI alloys was investigated on Gleeble- 3500 thermomechanical simulator, at a temperature range of 1050-1200 ℃ with an interval of 50℃ and a strain rate...The hot deformation behavior of powder met- allurgical （PM） TiAI alloys was investigated on Gleeble- 3500 thermomechanical simulator, at a temperature range of 1050-1200 ℃ with an interval of 50℃ and a strain rate range of 0.001-1.000 s-1. The results show that the flow stress of PM TiAI alloy is sensitive to deformation tem- perature and strain rate, the peak stress decreases with the increase in deformation temperature and decrease in strain rate, and dynamic recrystallization occurs during the hot compression. The deformation active energy was calcu- lated and the flow stress model during high-temperature deformation was established based on the Arrhenius equations and Zener-Hollomon parameter. The deformed microstructure consists of refined homogeneous γ and α2/γ grains.展开更多
A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 ...A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.展开更多
With the environmental regulations becoming more stringent and awareness of consumers increasing to protect environment, an urgent problem is to reduce the use of volatile organic compounds (VOCs). Powder coating is a...With the environmental regulations becoming more stringent and awareness of consumers increasing to protect environment, an urgent problem is to reduce the use of volatile organic compounds (VOCs). Powder coating is a kind of solid powder coating without any solvent. Due to its excellent application performance and environment-friendly, it is widely used in the field of metal coating, especially appliances of offices and home. In recent years, the use of powder coatings has been developed very fast and the requirements of functional powder coatings are also gradually strengthened. According to resin of the film forming, powder coatings can be divided into two types: thermosetting powder coatings and thermoplastic powder coatings. Each kind of powder coatings has its own advantages and disadvantages, and they will be applied in different fields. In order to improve the properties of powder coatings, there are many reports and studies about them. The compositions of powder coatings were extruded, crushed and screened to gain powder of coating. The powder always was stored at room temperature. The powder coatings often operated by two kinds which were electrostatic spraying method and fluidized bed dipping method. After that, the powder was heated to melt and cure. Finally, a smooth bright permanent film on articles was formed to achieve the purpose of decoration and corrosion. The process flow preparation of powder coatings always separated into dry process production and wet process production. The development courses of powder coatings about resins, pigments and fillers are summarized. The future development trends of powder coatings are illustrated.展开更多
The expressions of fluid velocity under several conditions during gas atomization according to the unsteady flow mechanics are propsed, and the basic ways to maintain the stability of fluid flow is analyzed
The influence of three different Al2O3 powder art self-flowing alumina castabie was studied , Max-imum compaction of sample wascomputed by An-dresen Equation . The result showed that the Al2O3 powder, which has much s...The influence of three different Al2O3 powder art self-flowing alumina castabie was studied , Max-imum compaction of sample wascomputed by An-dresen Equation . The result showed that the Al2O3 powder, which has much smaller particle size, could improve the microstructure and the mechanical properties of castabie under room temperature and high temperature. With the same powder size, the room temperature strength of the castabie added with Al2O3 powder properties of which were altered by adding mineralizing agent, was higher than that of the castabie added with common Al2O3 powder, but the flowability of these three different castabie was almost thesame.展开更多
文摘Powder flow behaviour is the result of countless combinations of interparticle forces of different natures: frictional,interlocking,cohesive and adhesive forces.We identify the rheological tests where one mechanism is most likely to dominate over the rest,and we propose the best descriptors of uniquely cohesive or frictional effects.We describe the procedure for a fluidisation test and the features of the results linked to powder cohesivity.We contrast these features against shear test results to determine powder frictional properties,explaining the conditions and limitations of the analysis.We use solid volume fraction and compressibility measurements to assess the extent to which the different mechanisms influence natural packing and forced flow in intermediate stress regimes.The proposed experimental protocol and framework of interpretation is applied to a wide range of powdered materials,representing typical industrial issues.The qualities of the characterisation are discussed and compared to those associated with traditional rheological testing methods.The framework successfully differentiates the effects of the various interparticle interaction mechanisms on powder flow,enabling a comprehensive prediction of powder behaviour in a variety of handling and processing settings.The metrics used are all normalised,allowing for a universal direct comparison of flowability across completely different materials.
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.
文摘In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the ]enike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.
基金funding from CSIR(MLP100926)and SERB(DST,Govt.of India)(CRG//2023/001897-G)for this work.
文摘The use of single and twin-screw extruders for solid-phase reactions is a promising method to intensify a process in a more sustainable manner.In this manuscript,we report a detailed analysis of the residence time distribution(RTD)in vertical single-screw reactors.The results will help in the selection of the right screw design that would help achieve the desired residence time,which is necessary for a reaction to happen.Experiments were conducted in three vertical screw reactors(having fixed shaft diameter)with varying dimensions using granular free-flowing powders of sodium chloride and silica with a mean particle size of∼25μm.RTD behavior was modeled using the radial particle velocities in the screw reactor's centrifugal field.Further,a method is proposed for estimating the axial dispersion coefficient of dry powders in such sheared flows using true and bulk densities of the powder and the screw shear rate.This dispersion coefficient is used in the axially dispersed plug flow model to describe the RTD behavior of screw reactors with acceptable accuracy.The theoretically predicted and experimentally obtained dispersion coefficients are found to be similar thereby confirming the suitability of the model.
基金the support received from Suzhou Kunlun Advanced Manufacturing Technologies and Equipment Co.,Ltd
文摘To investigate the hot deformation behavior of powder-forged （P/F） Fe-0. 5C：-2Cu steel, the hot compres- sion tests were conducted at temperatures ranging from 900 to 1000 ℃ and strain rates from 0.1 to 10 s-1 using Gleeble-1500 thermal simulator. The true stress-true strain curves at different temperatures and strain rates of P/F steel were obtained. It is found that dynamic recovery only occurs as strain rate is 10 s 1 at 900 ℃, and the dynamic recrystallization is the main softening mechanism. The flow stress increases with decreasing temperature and increas- ing strain rate. The experimental data are employed to develop constitutive equations on the basis of the Arrhenius- type equation by introducing the strain with nonlinear fitting. The flow stresses prediel：ed by the proposed constitu- tive equations are in good agreement with the experimental values, and the correlation coefficient （R2） and the aver- age absolute relative error （AARE） are 0. 995 25 and 3.07% respectively. These results indicate the proposed consti- tutive equations can effectively describe the hot deformation behavior of the material.
文摘A screw powder feeder is an important device for industrial applications. There are many parameters which affect the performance of the screw powder feeder, such as the shapes of the helical screw impeller, the number of screw pitches, etc. This paper presents an analysis of a gas-solid two-phase through screw powder feeder by using a commercial Computational Fluid Dynamics（CFD） code, Fluent. The K-ε model is used to simulate gas flow. Particle trajectory is obtained by the use of a discrete phase model. The results show the effects of gas velocity and panicle size on the transportation performance.
基金the National Natural Science Foundation of China(Project No.51675226)Natural Science Foundation of Liaoning Province(Project No.20180550167)Key Projects of Liaoning Province(Project Nos.LJ2017ZL001,LJ2019ZL005).
文摘To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.
基金supported by the National Natural Science Foundation of China (Nos. 51301157 and 51105102)the National High Technology Research and Development Program (No. 2013AA031103)
文摘The hot deformation behavior of powder met- allurgical （PM） TiAI alloys was investigated on Gleeble- 3500 thermomechanical simulator, at a temperature range of 1050-1200 ℃ with an interval of 50℃ and a strain rate range of 0.001-1.000 s-1. The results show that the flow stress of PM TiAI alloy is sensitive to deformation tem- perature and strain rate, the peak stress decreases with the increase in deformation temperature and decrease in strain rate, and dynamic recrystallization occurs during the hot compression. The deformation active energy was calcu- lated and the flow stress model during high-temperature deformation was established based on the Arrhenius equations and Zener-Hollomon parameter. The deformed microstructure consists of refined homogeneous γ and α2/γ grains.
基金Project(50675210) supported by the National Natural Science Foundation of ChinaProject(03022) supported by the Key Science Research Program of Education Ministry of ChinaProject(200410250) supported by the Youth Science Foundation of Shanxi Province, China
文摘A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.
文摘With the environmental regulations becoming more stringent and awareness of consumers increasing to protect environment, an urgent problem is to reduce the use of volatile organic compounds (VOCs). Powder coating is a kind of solid powder coating without any solvent. Due to its excellent application performance and environment-friendly, it is widely used in the field of metal coating, especially appliances of offices and home. In recent years, the use of powder coatings has been developed very fast and the requirements of functional powder coatings are also gradually strengthened. According to resin of the film forming, powder coatings can be divided into two types: thermosetting powder coatings and thermoplastic powder coatings. Each kind of powder coatings has its own advantages and disadvantages, and they will be applied in different fields. In order to improve the properties of powder coatings, there are many reports and studies about them. The compositions of powder coatings were extruded, crushed and screened to gain powder of coating. The powder always was stored at room temperature. The powder coatings often operated by two kinds which were electrostatic spraying method and fluidized bed dipping method. After that, the powder was heated to melt and cure. Finally, a smooth bright permanent film on articles was formed to achieve the purpose of decoration and corrosion. The process flow preparation of powder coatings always separated into dry process production and wet process production. The development courses of powder coatings about resins, pigments and fillers are summarized. The future development trends of powder coatings are illustrated.
文摘The expressions of fluid velocity under several conditions during gas atomization according to the unsteady flow mechanics are propsed, and the basic ways to maintain the stability of fluid flow is analyzed
文摘The influence of three different Al2O3 powder art self-flowing alumina castabie was studied , Max-imum compaction of sample wascomputed by An-dresen Equation . The result showed that the Al2O3 powder, which has much smaller particle size, could improve the microstructure and the mechanical properties of castabie under room temperature and high temperature. With the same powder size, the room temperature strength of the castabie added with Al2O3 powder properties of which were altered by adding mineralizing agent, was higher than that of the castabie added with common Al2O3 powder, but the flowability of these three different castabie was almost thesame.
