The local solid flow structure of a bubbling fluidized bed of sand particles was investigated m three different columns to characterize the properties of clusters. The experiments were performed using a reflective opt...The local solid flow structure of a bubbling fluidized bed of sand particles was investigated m three different columns to characterize the properties of clusters. The experiments were performed using a reflective optical fiber probe. The variations in size, velocity, and void fraction of the clusters due to changes in the superficial gas velocity, particle size, and radial positions were studied. The results indicate that the velocity of the clusters remained unchanged while their size increased as the column diameter increased. In addition, the radial profile of the clusters＇ velocity did not depend on the radial position. The results indicate that larger particles form larger clusters, which move slower.展开更多
The process of sinteri ng of several particles in con tact via a viscous flow mecha nism was studied numerically using computational fluid dynamics. The volume of fluid technique within a finite volume method was used...The process of sinteri ng of several particles in con tact via a viscous flow mecha nism was studied numerically using computational fluid dynamics. The volume of fluid technique within a finite volume method was used to simulate bridge formation between particles, as well as densification at different configurational states of the particles. The method was validated by comparing results for two-particle coalescence with the literature.The effect of the numberof particles on agglomerati on kin etics was studied by comparing bridge growth rate for systems having different numbers of particles in a chain. Although increasing the number of particles led to a decrease in the local bridge growth rate and to slower equilibration, there were no marked differences, when the overall volume of the system was considered. The effect of coordination number on the densification rate was directly studied by changing the number of particles in contact with a central particle.Increasing the coordination nurnbec caused the overall rate of densificatio n to in crease, but delayed equilibration, analogous to steric effects. These findi ngs describe the con figurational state of agglomerates, typical of mesoscale caking. In a multi-scale study, they can be used to characterize caking at a bulk scale to partly address the lack of experimental data in this field.展开更多
Particle-particle and particle-wall collisions in gas-solid fluidized beds lead to charge accumulation on particles.This work evaluated the effect of fluidization time on charge transfer and bipolar charging(charge se...Particle-particle and particle-wall collisions in gas-solid fluidized beds lead to charge accumulation on particles.This work evaluated the effect of fluidization time on charge transfer and bipolar charging(charge separation)and their influence on hydrodynamic structures in a fluidized bed.Experiments were performed with glass beads and polyethylene particles in a glass column.The pressure fluctuations and net electrostatic charge of particles were measured during fluidization.Wavelet and short-time Fourier transforms were used to analyze pressure fluctuations.The results revealed that bipolar charging is the dominant tribocharging mechanism in a bed of glass beads.Bipolar charging in a bed of particles with a narrow size distribution does not affect either hydrodynamic structures or the transition velocity to the turbulent regime.A large difference between the work functions of the wall and particle in the bed of polyethylene particles leads to high charge transfer.Formation of a stagnant particle layer on the wall eventually causes the energy of macro-structures to increase to its maximum.At longer fluidization times,the macro-structural energy decreases and bubbles shrink until the electrostatic charge reaches the equilibrium level.These results well describe the effect of fluidization time on hydrodynamic structures.展开更多
A nonlinear model representing oxygen diffusion accompanied by the Michaelis-Menten consumption kinetics inside a spherical cell is solved analytically by the differential transform method （DTM） and the modified Ado...A nonlinear model representing oxygen diffusion accompanied by the Michaelis-Menten consumption kinetics inside a spherical cell is solved analytically by the differential transform method （DTM） and the modified Adomian decomposition method （MADM）. A perfect agreement between the literature data and the results from the proposed展开更多
文摘The local solid flow structure of a bubbling fluidized bed of sand particles was investigated m three different columns to characterize the properties of clusters. The experiments were performed using a reflective optical fiber probe. The variations in size, velocity, and void fraction of the clusters due to changes in the superficial gas velocity, particle size, and radial positions were studied. The results indicate that the velocity of the clusters remained unchanged while their size increased as the column diameter increased. In addition, the radial profile of the clusters＇ velocity did not depend on the radial position. The results indicate that larger particles form larger clusters, which move slower.
文摘The process of sinteri ng of several particles in con tact via a viscous flow mecha nism was studied numerically using computational fluid dynamics. The volume of fluid technique within a finite volume method was used to simulate bridge formation between particles, as well as densification at different configurational states of the particles. The method was validated by comparing results for two-particle coalescence with the literature.The effect of the numberof particles on agglomerati on kin etics was studied by comparing bridge growth rate for systems having different numbers of particles in a chain. Although increasing the number of particles led to a decrease in the local bridge growth rate and to slower equilibration, there were no marked differences, when the overall volume of the system was considered. The effect of coordination number on the densification rate was directly studied by changing the number of particles in contact with a central particle.Increasing the coordination nurnbec caused the overall rate of densificatio n to in crease, but delayed equilibration, analogous to steric effects. These findi ngs describe the con figurational state of agglomerates, typical of mesoscale caking. In a multi-scale study, they can be used to characterize caking at a bulk scale to partly address the lack of experimental data in this field.
文摘Particle-particle and particle-wall collisions in gas-solid fluidized beds lead to charge accumulation on particles.This work evaluated the effect of fluidization time on charge transfer and bipolar charging(charge separation)and their influence on hydrodynamic structures in a fluidized bed.Experiments were performed with glass beads and polyethylene particles in a glass column.The pressure fluctuations and net electrostatic charge of particles were measured during fluidization.Wavelet and short-time Fourier transforms were used to analyze pressure fluctuations.The results revealed that bipolar charging is the dominant tribocharging mechanism in a bed of glass beads.Bipolar charging in a bed of particles with a narrow size distribution does not affect either hydrodynamic structures or the transition velocity to the turbulent regime.A large difference between the work functions of the wall and particle in the bed of polyethylene particles leads to high charge transfer.Formation of a stagnant particle layer on the wall eventually causes the energy of macro-structures to increase to its maximum.At longer fluidization times,the macro-structural energy decreases and bubbles shrink until the electrostatic charge reaches the equilibrium level.These results well describe the effect of fluidization time on hydrodynamic structures.
文摘A nonlinear model representing oxygen diffusion accompanied by the Michaelis-Menten consumption kinetics inside a spherical cell is solved analytically by the differential transform method （DTM） and the modified Adomian decomposition method （MADM）. A perfect agreement between the literature data and the results from the proposed
