Fluidization of fine cohesive powders is seriously restricted by the strong interparticle cohesion. The rational combination of nanoparticles with fine cohesive powders is expected to obtain composite par- ticles with...Fluidization of fine cohesive powders is seriously restricted by the strong interparticle cohesion. The rational combination of nanoparticles with fine cohesive powders is expected to obtain composite par- ticles with improved flowability. In this work, we firstly reviewed the sandwich and three-point contact models regarding the fundamental principles of nano-additives in reducing cohesiveness. Based on these previous models, the effects of the size of nanoparticles, their agglomeration and coverage on the surface of cohesive powders in reducing interparticle forces were theoretically analyzed. To validate the the- ory effectiveness for the irregularly shaped cohesive powders, an extreme case of cubic powders coated with silica nanoparticles was fabricated, and the flowability of the composite particles was determined experimentally. Ultimately, based oN force balance of a single particle, a semi-theoretical criterion for predicting the fluidization behavior of coated powders was developed to guide the practical applications of improving the flowability of cohesive powders through structural design and modulation.展开更多
Characterisation of flowability of small quantities of cohesive powders is of great industrial interest, particularly for the pharmaceutical sec- tors, where a limited amount of material is available or the material i...Characterisation of flowability of small quantities of cohesive powders is of great industrial interest, particularly for the pharmaceutical sec- tors, where a limited amount of material is available or the material is not easily accessible. In this paper, ball indentation on a powder bed is evaluated for flow characterisation of small quantities of cohesive powders at low levels of consolidation pressures. In parallel, the bulk powder is subjected to the common test method of unconfined direct compression. Analogous to indentation hardness testing, for which the indentation pressure is related to the flow stress, a constraint factor (C) is defined relating the unconfined yield stress and indentation pres- sure. The constraint factors for the test powders have been evaluated, enabling an easy method to characterize the flow behaviour of cohesive powders.展开更多
Deagglomeration of cohesive particles in combination with coarse carrier is a key requirement for inhaled formulations.The aim of the project was to propose a mathematical approach to understand aerosolization behavio...Deagglomeration of cohesive particles in combination with coarse carrier is a key requirement for inhaled formulations.The aim of the project was to propose a mathematical approach to understand aerosolization behaviour of micronized particles alone and in formulation with carriers.Salbutamol sulphate and salmeterol xinafoate were blended separately with fine lactose(ratio 1:4)and fine and coarse lactose(1:4:63.5).Laser diffraction was employed to characterize the powder median particle size.The deagglomeration of micronized materials followed an asymptotic monoexponential relationship.When the coarse lactose was added,the relationship fitted a bi-exponential equation showing an easily and a poorly dispersed fraction.Using model hydrophobic and hydrophilic APIs,this study has demonstrated the utility of an analytical approach that can parameterize deagglomeration behaviour of carrier-free and carrier-based inhalation formulations.The analytical approach provides the ability to systematically study the effect of material,formulation and processing factors on deagglomeration behaviour.展开更多
The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted ...The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted fluidized bed.The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO2 powders,the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization.The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200μm.Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity.The stirring applied enlarges the operational range of agglomerate particulate fluidization(APF)with a delayed onset of bubbling for cohesive particles.However,the exorbitant speed increases the collision velocity and contact area between small agglomerates,which results in the formation of unstable agglomerates and the whirlpool of powder.展开更多
The fundamentals of cohesive powder consolidation and flow behaviour using a reasonable combination of particle and continuum mechanics are explained. By means of the model 搒tiff particles with soft contacts? the inf...The fundamentals of cohesive powder consolidation and flow behaviour using a reasonable combination of particle and continuum mechanics are explained. By means of the model 搒tiff particles with soft contacts? the influ-ence of elastic-plastic repulsion in particle contacts is demonstrated. With this as the physical basis, the stationary yield locus, instantaneous yield loci and consolidation loci, flow function and compression function are presented. The flow properties of a very cohesive titania nanopowder (dS=200 nm) are shown. These models are used to evaluate shear cell test results as constitutive functions for computer aided apparatus design for reliable powder flow.展开更多
The measurement of powder flowability is a major concern for most industrial processes that deal with the handling of bulk solids as raw materials, intermediates, or products. The development of devices that measure t...The measurement of powder flowability is a major concern for most industrial processes that deal with the handling of bulk solids as raw materials, intermediates, or products. The development of devices that measure the flowability of non-aerated powders has not progressed as rapidly as might have been hoped since most research activities have been based on various types of shear testers intended to aid the design of hoppers. A new flowability indicator named as weighted cohesion (WS) is established using newly improved version of direct cohesion texture. A cornerstone of the proposed technique is that the procedure is automated, using a digital Warren Spring tester called Warren Spring-University of Malaya cohesion tester (WSUMCT), thus making results operator-insensitive. Besides being a practical tool to diagnose the cohesion of experimental powders, the ratio between measured cohesion (using WSUMCT) and aerated density (using Hosokawa PT-S) provides us with a powerful technique to research fundamental particle internal cohesion forces directly and use these data to indicate the flowability. In this work, a series of fine (9.4μm) and coarse (60 μm) porous silica gel particle mixtures, and mixtures of fine (28μm) and coarse (72 μm) glass ballotini as well, were used as test powders. The results from these tests agree well with relative flowability determined on our newly driven indicator using WSUMCT. The validation of aerated weighted cohesion (WSA) as a flowability indicator was authenticated by comparing the conducted parameter with established measured Hausner ratio (HR) and angle of repose (AoR).展开更多
The arch formation mechanism and discharge process of a very cohesive fine powder(calcium carbonate)in a vibrated silo was investigated by experiments and discrete element method(DEM)simulations.An experimental setup ...The arch formation mechanism and discharge process of a very cohesive fine powder(calcium carbonate)in a vibrated silo was investigated by experiments and discrete element method(DEM)simulations.An experimental setup is built to study the flow behaviors with the proposed image-based flow rate measurement method.A cohesive DEM model is used to investigate the dynamic behaviors of the powder bed.Results indicate that the arch formation depends on the vibration acceleration amplitude and is slightly affected by the frequency.The powder discharge flow rate increases with vibration acceleration amplitude and decreases with frequency.When the acceleration amplitude exceeds 15 g,the flow rate tends to stabilize.When the acceleration amplitude exceeds 1 g,there is separation and collision between the powder bed and the silo bottom.This collision leads to a significant increase in the contact force.展开更多
Fine and ultrafine particles possess great potential for industrial applications ascribed from their huge specific surface area and ability to provide good gas–solid contact.However,these powders are inherently cohes...Fine and ultrafine particles possess great potential for industrial applications ascribed from their huge specific surface area and ability to provide good gas–solid contact.However,these powders are inherently cohesive,making it challenging to achieve smooth flow and fluidization.This challenge can be well-resolved by nanoparticle modulation(nano-modulation),where a small amount of nanoparticles is uniformly mixed with the cohesive fine/ultrafine powders.Through nano-modulation,the fluidization system of cohesive powders exhibits distinguishable minimum fluidization velocity,enlarged bed expansion ratio(particularly the dense phase expansion),and scarcer,smaller,and slower moving bubbles,indicating improved flow and fluidization quality.The purpose of the current work is to systematically summarize the state-of-the-art progress in the fluidization and utilization of fine and ultrafine particles via the nanoparticle modulation method.Accordingly,a broader audience can be enlightened regarding this promising fine/ultrafine particle fluidization technology,so as to provoke their attention and encourage interdisciplinary integration and industry-academia collaborative research.展开更多
The propagation velocity (Vs) of an ultrasonic signal through a granular material depends on the type of interparticle contact. For noncohesive glass beads, a power law behavior Vs α σc1/6 for consolidation stress...The propagation velocity (Vs) of an ultrasonic signal through a granular material depends on the type of interparticle contact. For noncohesive glass beads, a power law behavior Vs α σc1/6 for consolidation stresses applied (σc) above 1 MPa has been measured in previous work. This equation is compatible with Hertz's interaction law between elastic solids. In the present work, we have tested the propagation velocity of ultrasound signals through a sample of fine powder. The tensile strength and compactivity of the powder were previously measured by means of the Seville powder tester (SPT), indicating plastic deformation of the surface asperities in contact for small to moderate consolidation stresses. However, the measurements of ultrasound propagation at high consolidations presented here are compatible with Hertz's law. This finding suggests that for high consolidation stresses, surface asperities are flattened, and it is therefore the elastic deformation of the bulk of the particles that determines the transmission of ultrasonic pulses.展开更多
基金The authors acknowledge the financial supports provided by the National Key Research and Development Program (No. 2016YFA0200101), the National Natural Science Foundation of China (Nos. 21306102 and 21422604) and the China Postdoctoral Science Foundation (No. 2015M571049).
文摘Fluidization of fine cohesive powders is seriously restricted by the strong interparticle cohesion. The rational combination of nanoparticles with fine cohesive powders is expected to obtain composite par- ticles with improved flowability. In this work, we firstly reviewed the sandwich and three-point contact models regarding the fundamental principles of nano-additives in reducing cohesiveness. Based on these previous models, the effects of the size of nanoparticles, their agglomeration and coverage on the surface of cohesive powders in reducing interparticle forces were theoretically analyzed. To validate the the- ory effectiveness for the irregularly shaped cohesive powders, an extreme case of cubic powders coated with silica nanoparticles was fabricated, and the flowability of the composite particles was determined experimentally. Ultimately, based oN force balance of a single particle, a semi-theoretical criterion for predicting the fluidization behavior of coated powders was developed to guide the practical applications of improving the flowability of cohesive powders through structural design and modulation.
文摘Characterisation of flowability of small quantities of cohesive powders is of great industrial interest, particularly for the pharmaceutical sec- tors, where a limited amount of material is available or the material is not easily accessible. In this paper, ball indentation on a powder bed is evaluated for flow characterisation of small quantities of cohesive powders at low levels of consolidation pressures. In parallel, the bulk powder is subjected to the common test method of unconfined direct compression. Analogous to indentation hardness testing, for which the indentation pressure is related to the flow stress, a constraint factor (C) is defined relating the unconfined yield stress and indentation pres- sure. The constraint factors for the test powders have been evaluated, enabling an easy method to characterize the flow behaviour of cohesive powders.
文摘Deagglomeration of cohesive particles in combination with coarse carrier is a key requirement for inhaled formulations.The aim of the project was to propose a mathematical approach to understand aerosolization behaviour of micronized particles alone and in formulation with carriers.Salbutamol sulphate and salmeterol xinafoate were blended separately with fine lactose(ratio 1:4)and fine and coarse lactose(1:4:63.5).Laser diffraction was employed to characterize the powder median particle size.The deagglomeration of micronized materials followed an asymptotic monoexponential relationship.When the coarse lactose was added,the relationship fitted a bi-exponential equation showing an easily and a poorly dispersed fraction.Using model hydrophobic and hydrophilic APIs,this study has demonstrated the utility of an analytical approach that can parameterize deagglomeration behaviour of carrier-free and carrier-based inhalation formulations.The analytical approach provides the ability to systematically study the effect of material,formulation and processing factors on deagglomeration behaviour.
基金The authors are grateful to the support by the National Natural Science Foundation of China(Grant Nos.21908227,21736010 and 22178363).
文摘The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted fluidized bed.The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO2 powders,the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization.The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200μm.Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity.The stirring applied enlarges the operational range of agglomerate particulate fluidization(APF)with a delayed onset of bubbling for cohesive particles.However,the exorbitant speed increases the collision velocity and contact area between small agglomerates,which results in the formation of unstable agglomerates and the whirlpool of powder.
文摘The fundamentals of cohesive powder consolidation and flow behaviour using a reasonable combination of particle and continuum mechanics are explained. By means of the model 搒tiff particles with soft contacts? the influ-ence of elastic-plastic repulsion in particle contacts is demonstrated. With this as the physical basis, the stationary yield locus, instantaneous yield loci and consolidation loci, flow function and compression function are presented. The flow properties of a very cohesive titania nanopowder (dS=200 nm) are shown. These models are used to evaluate shear cell test results as constitutive functions for computer aided apparatus design for reliable powder flow.
文摘The measurement of powder flowability is a major concern for most industrial processes that deal with the handling of bulk solids as raw materials, intermediates, or products. The development of devices that measure the flowability of non-aerated powders has not progressed as rapidly as might have been hoped since most research activities have been based on various types of shear testers intended to aid the design of hoppers. A new flowability indicator named as weighted cohesion (WS) is established using newly improved version of direct cohesion texture. A cornerstone of the proposed technique is that the procedure is automated, using a digital Warren Spring tester called Warren Spring-University of Malaya cohesion tester (WSUMCT), thus making results operator-insensitive. Besides being a practical tool to diagnose the cohesion of experimental powders, the ratio between measured cohesion (using WSUMCT) and aerated density (using Hosokawa PT-S) provides us with a powerful technique to research fundamental particle internal cohesion forces directly and use these data to indicate the flowability. In this work, a series of fine (9.4μm) and coarse (60 μm) porous silica gel particle mixtures, and mixtures of fine (28μm) and coarse (72 μm) glass ballotini as well, were used as test powders. The results from these tests agree well with relative flowability determined on our newly driven indicator using WSUMCT. The validation of aerated weighted cohesion (WSA) as a flowability indicator was authenticated by comparing the conducted parameter with established measured Hausner ratio (HR) and angle of repose (AoR).
文摘The arch formation mechanism and discharge process of a very cohesive fine powder(calcium carbonate)in a vibrated silo was investigated by experiments and discrete element method(DEM)simulations.An experimental setup is built to study the flow behaviors with the proposed image-based flow rate measurement method.A cohesive DEM model is used to investigate the dynamic behaviors of the powder bed.Results indicate that the arch formation depends on the vibration acceleration amplitude and is slightly affected by the frequency.The powder discharge flow rate increases with vibration acceleration amplitude and decreases with frequency.When the acceleration amplitude exceeds 15 g,the flow rate tends to stabilize.When the acceleration amplitude exceeds 1 g,there is separation and collision between the powder bed and the silo bottom.This collision leads to a significant increase in the contact force.
文摘Fine and ultrafine particles possess great potential for industrial applications ascribed from their huge specific surface area and ability to provide good gas–solid contact.However,these powders are inherently cohesive,making it challenging to achieve smooth flow and fluidization.This challenge can be well-resolved by nanoparticle modulation(nano-modulation),where a small amount of nanoparticles is uniformly mixed with the cohesive fine/ultrafine powders.Through nano-modulation,the fluidization system of cohesive powders exhibits distinguishable minimum fluidization velocity,enlarged bed expansion ratio(particularly the dense phase expansion),and scarcer,smaller,and slower moving bubbles,indicating improved flow and fluidization quality.The purpose of the current work is to systematically summarize the state-of-the-art progress in the fluidization and utilization of fine and ultrafine particles via the nanoparticle modulation method.Accordingly,a broader audience can be enlightened regarding this promising fine/ultrafine particle fluidization technology,so as to provoke their attention and encourage interdisciplinary integration and industry-academia collaborative research.
基金supported by the Spanish Government Agency Ministerio de Ciencia y Tecnologia (contract FIS2006-03645) Junta de Andalucia (contract FQM 5735)
文摘The propagation velocity (Vs) of an ultrasonic signal through a granular material depends on the type of interparticle contact. For noncohesive glass beads, a power law behavior Vs α σc1/6 for consolidation stresses applied (σc) above 1 MPa has been measured in previous work. This equation is compatible with Hertz's interaction law between elastic solids. In the present work, we have tested the propagation velocity of ultrasound signals through a sample of fine powder. The tensile strength and compactivity of the powder were previously measured by means of the Seville powder tester (SPT), indicating plastic deformation of the surface asperities in contact for small to moderate consolidation stresses. However, the measurements of ultrasound propagation at high consolidations presented here are compatible with Hertz's law. This finding suggests that for high consolidation stresses, surface asperities are flattened, and it is therefore the elastic deformation of the bulk of the particles that determines the transmission of ultrasonic pulses.