The phenomenon of particle interaction involved in pulmonary drug delivery belongs to a wide variety of disciplines of particle technology, in particular, fluidization. This paper reviews the basic concepts of pulmona...The phenomenon of particle interaction involved in pulmonary drug delivery belongs to a wide variety of disciplines of particle technology, in particular, fluidization. This paper reviews the basic concepts of pulmonary drug delivery with references to fluidization research, in particular, studies on Geldart group C powders. Dry powder inhaler device-formulation combination has been shown to be an effective method for delivering drugs to the lung for treatment of asthma, chronic obstructive pulmonary disease and cystic fibrosis. Even with advanced designs, however, delivery efficiency is still poor mainly due to powder dispersion problems which cause poor lung deposition and high dose variability. Drug particles used in current inhalers must be 1–5 μm in diameter for effective deposition in small-diameter airways and alveoli. These powders are very cohesive, have poor flowability, and are difficult to disperse into aerosol due to cohesion arising from van der Waals attraction. These problems are well known in fluidization research, much of which is highly relevant to pulmonary drug delivery.展开更多
The influence of gas type （helium and argon） and bed temperature （77-473 K） on the fluidization behaviour of Geldart groups C and A particles was investigated. For both types of particles tested, i.e., Al2O3 （4.8...The influence of gas type （helium and argon） and bed temperature （77-473 K） on the fluidization behaviour of Geldart groups C and A particles was investigated. For both types of particles tested, i.e., Al2O3 （4.8μm） and glass beads （39 μm）, the fluidization quality in different gases shows the following priority sequence： Ar 〉 He. In the same gaseous atmosphere, the particles when fluidized at an elevated temperature usually show larger bed voidages, higher bed pressure drops, and a lower Umf for the group A powder, all indicating an enhancement in fluidization quality. Possible mechanisms governing the operations of gas type and temperature in influencing the fluidization behaviours of fine particles have been discussed with respect to the changes in both gas properties and interparticle forces （on the basis of the London-van der Waals theory）. Gas viscosity （varying significantly with gas-type and temperature） proves to be the key parameter that influences the bed pressure drops and Umf in fluidization of fine particles, while the interparticle forces （also varying with gas-type and temperature） may play an important role in fine-particle fluidization by affecting the expansion behaviour of the particle-bed.展开更多
Previous reports and current studies show that fluidization of some Geldart A particles is enhanced by increasing bed temperature. Both the averaged local particle concentration and the particle concentration in the d...Previous reports and current studies show that fluidization of some Geldart A particles is enhanced by increasing bed temperature. Both the averaged local particle concentration and the particle concentration in the dense phase decrease with increasing bed temperature, at constant superficial gas velocities. However, conventional models fail to predict these changes, because the role of interparticle forces is usually neglected at different bed temperatures. Here, the interparticle forces are analyzed to explore the mechanism of gas-solid fluidization at high temperatures. Indeed, as the temperature increases, the interparticle attractive forces decrease while the interparticle repulsive forces increase. Consequently, fluidization behaviors of some Geldart A particles seem to increasingly shift from typical Geldart A towards B with increasing temperature.展开更多
Based on a first-principles approach,we establish an alternating-current（AC） relaxation theory for a rotating metallic particle with complex dielectric constant εα=εα-iσα/ω0.Here εα is the real part,σα th...Based on a first-principles approach,we establish an alternating-current（AC） relaxation theory for a rotating metallic particle with complex dielectric constant εα=εα-iσα/ω0.Here εα is the real part,σα the conductivity,ω0 the angular frequency of an AC electric field,and i=-11/2.Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges（described by εα） and free charges（corresponding to σα）,contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.展开更多
The bulk flow properties of four different fly ashes were assessed at ambient temperature and at 500 ~C, using a high temperature annular shear cell. These powders all resulted from industrial processes and had simila...The bulk flow properties of four different fly ashes were assessed at ambient temperature and at 500 ~C, using a high temperature annular shear cell. These powders all resulted from industrial processes and had similar chemical compositions but different particle size distributions. Applying a high temperature was found to increase the powder cohesion, with this effect being more significant in the case of the sample with the highest proportion of fines. To better understand the effect of temperature on the bulk flow properties of these materials, a model previously proposed by some of the authors was used to correlate the powder isostatic tensile strength with the interparticle forces and microscale particle contact struc- ture. This model combines the continuum approach with description of particle-to-particle interactions. A comparison with experimental data indicated that the effects of consolidation and temperature on the tensile strength of the fly ashes were correctly described by the model. This theoretical approach also elucidates the mechanism by which the temperature affects the bulk flow properties of fly ashes through modifications of the microscale intemarticle contacts.展开更多
文摘The phenomenon of particle interaction involved in pulmonary drug delivery belongs to a wide variety of disciplines of particle technology, in particular, fluidization. This paper reviews the basic concepts of pulmonary drug delivery with references to fluidization research, in particular, studies on Geldart group C powders. Dry powder inhaler device-formulation combination has been shown to be an effective method for delivering drugs to the lung for treatment of asthma, chronic obstructive pulmonary disease and cystic fibrosis. Even with advanced designs, however, delivery efficiency is still poor mainly due to powder dispersion problems which cause poor lung deposition and high dose variability. Drug particles used in current inhalers must be 1–5 μm in diameter for effective deposition in small-diameter airways and alveoli. These powders are very cohesive, have poor flowability, and are difficult to disperse into aerosol due to cohesion arising from van der Waals attraction. These problems are well known in fluidization research, much of which is highly relevant to pulmonary drug delivery.
文摘The influence of gas type （helium and argon） and bed temperature （77-473 K） on the fluidization behaviour of Geldart groups C and A particles was investigated. For both types of particles tested, i.e., Al2O3 （4.8μm） and glass beads （39 μm）, the fluidization quality in different gases shows the following priority sequence： Ar 〉 He. In the same gaseous atmosphere, the particles when fluidized at an elevated temperature usually show larger bed voidages, higher bed pressure drops, and a lower Umf for the group A powder, all indicating an enhancement in fluidization quality. Possible mechanisms governing the operations of gas type and temperature in influencing the fluidization behaviours of fine particles have been discussed with respect to the changes in both gas properties and interparticle forces （on the basis of the London-van der Waals theory）. Gas viscosity （varying significantly with gas-type and temperature） proves to be the key parameter that influences the bed pressure drops and Umf in fluidization of fine particles, while the interparticle forces （also varying with gas-type and temperature） may play an important role in fine-particle fluidization by affecting the expansion behaviour of the particle-bed.
文摘Previous reports and current studies show that fluidization of some Geldart A particles is enhanced by increasing bed temperature. Both the averaged local particle concentration and the particle concentration in the dense phase decrease with increasing bed temperature, at constant superficial gas velocities. However, conventional models fail to predict these changes, because the role of interparticle forces is usually neglected at different bed temperatures. Here, the interparticle forces are analyzed to explore the mechanism of gas-solid fluidization at high temperatures. Indeed, as the temperature increases, the interparticle attractive forces decrease while the interparticle repulsive forces increase. Consequently, fluidization behaviors of some Geldart A particles seem to increasingly shift from typical Geldart A towards B with increasing temperature.
基金Project supported by the National Natural Science Foundation of China(Grant No.11222544)the Fok Ying Tung Education Foundation(Grant No.131008)+1 种基金the Program for New Century Excellent Talents in University,China(Grant No.NCET-12-0121)the National Key Basic Research Program of China(Grant No.2011CB922004)
文摘Based on a first-principles approach,we establish an alternating-current（AC） relaxation theory for a rotating metallic particle with complex dielectric constant εα=εα-iσα/ω0.Here εα is the real part,σα the conductivity,ω0 the angular frequency of an AC electric field,and i=-11/2.Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges（described by εα） and free charges（corresponding to σα）,contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.
文摘The bulk flow properties of four different fly ashes were assessed at ambient temperature and at 500 ~C, using a high temperature annular shear cell. These powders all resulted from industrial processes and had similar chemical compositions but different particle size distributions. Applying a high temperature was found to increase the powder cohesion, with this effect being more significant in the case of the sample with the highest proportion of fines. To better understand the effect of temperature on the bulk flow properties of these materials, a model previously proposed by some of the authors was used to correlate the powder isostatic tensile strength with the interparticle forces and microscale particle contact struc- ture. This model combines the continuum approach with description of particle-to-particle interactions. A comparison with experimental data indicated that the effects of consolidation and temperature on the tensile strength of the fly ashes were correctly described by the model. This theoretical approach also elucidates the mechanism by which the temperature affects the bulk flow properties of fly ashes through modifications of the microscale intemarticle contacts.
