We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with...We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments,numerical predictions have been successfully used to explain the influences of impeller rotating speed,particle density, particle size, liquid viscosity and initial solid loading on the solid suspension behavior,i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed(N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine(RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.展开更多
Hydrodynamics of carbon dioxide fluid-particle mixtures are predicted using a low density ratio-based kinetic theory of granular flow in high pressure carbon dioxide fluid fluidized beds.A coexistence of particle wave...Hydrodynamics of carbon dioxide fluid-particle mixtures are predicted using a low density ratio-based kinetic theory of granular flow in high pressure carbon dioxide fluid fluidized beds.A coexistence of particle waves and particle aggregates exists along bed height.The threshold to identify the occurrence of particle aggregates is suggested based on standard deviation of solid volume fractions in aggregative fluidization.The existence time fractions and frequencies of particle aggregates are predicted along axial direction.The effect of carbon dioxide fluid temperature and pressure on volume fraction and velocity distributions are analyzed at different inlet carbon dioxide velocities and particle densities in high pressure carbon dioxide fluidized beds.Simulated results indicate that the carbon dioxide-particles fluidization transits from particulate to aggregative states with the increase of inlet carbon dioxide ve-locities.The computed fluid volume fractions and heterogeneity indexes are close to the measurements in a high pressure carbon dioxide fluidized bed.展开更多
This paper presents a numerical and experimental study of the discharge rate of sawdust from an aerated hopper as an important parameter in many industrial processes involving the handling of other granular materials....This paper presents a numerical and experimental study of the discharge rate of sawdust from an aerated hopper as an important parameter in many industrial processes involving the handling of other granular materials. Numerical experiments are conducted by means of an Eulerian-Eulerian approach coupled with the kinetic theory of granular flow (KTGF). Emphasis is given to the effects of particle size, hopper outlet width, hopper half angle, aeration height and air flow rate. The results show that the discharge rate is significantly affected by hopper outlet width, particle size and air flow rate, but is not sensitive to the hopper half angle and aeration height: increasing hopper outlet width or air flow rate increases discharge rate, while increasing particle size decreases discharge rate. Close agreement between numerical predictions and experimental results is obtained.展开更多
The present work examines the predictive capability of a two-fluid CFD model that is based on the kinetic theory of granular flow in simulating dilute-phase turbulent liquid-particle pipe flows in which the inter- sti...The present work examines the predictive capability of a two-fluid CFD model that is based on the kinetic theory of granular flow in simulating dilute-phase turbulent liquid-particle pipe flows in which the inter- stitial fluid effect on the particle fluctuating motion is significant. The impacts of employing different drag correlations and turbulence closure models to describe the fluid-particle interactions (i.e. drag force and long-range interaction) are examined at both the mean and fluctuating velocity levels. The model pre- dictions are validated using experimental data of turbulent liquid-particle flows in a vertical pipe at different particle Reynolds numbers (Rep 〉 400 and Rep 〈 400), which characterize the importance of the vortex shedding phenomenon in the fluid-phase turbulence modulation. The results indicate that (1) the fluctuating velocity level predictions at different Rep are highly sensitive to the drag correlation selec- tion and (2) different turbulence closure models must be employed to accurately describe the long-range fluid-particle interaction in each phase. In general, good agreement is found between the model predic- tions and the experimental data at both the mean and fluctuating velocity levels provided that appropriate combinations of the drag correlation and the turbulence closure model are selected depending on Rep. 2009 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.展开更多
We present experimental investigations and numerical simulations of a pseudo-2D riser. Experiments were performed for various airflow rates, particle types/diameters, and particle size distributions. Pres- sure distri...We present experimental investigations and numerical simulations of a pseudo-2D riser. Experiments were performed for various airflow rates, particle types/diameters, and particle size distributions. Pres- sure distributions along the wall of the riser were measured, Additional measurements from a smaller pseudo-2D riser (Kallio et al., 2009; Shah et al., 2012) were used to analyze horizontal solids volume fraction profiles. The experimental data were compared with simulation results carried out using an Euler-Euler approach, A mesh sensitivity study was conducted for numerical simulations and effects associated with simplifying real 3D geometry to a 2D model were examined. In addition, the effect of using an algebraic equation to represent the granular temperature versus a full partial differential equation also was examined for numerical simulations. Results showed small but significant near-wall sensitivity of the flow variables to mesh size. Substantial differences in mean pressure, solids distribution, and solid velocities were obtained, when 2D and 3D simulation results were compared. Finally, applying the simplified granular temperature equation for turbulent fluidization and for dilute-phase transport can lead to incorrect predictions in models,展开更多
This short communication demonstrates why extreme caution has to be taken when applying conven- tional kinetic-frictional closures to continuum modeling of high shear granulation (HSG), Conventional models refer to ...This short communication demonstrates why extreme caution has to be taken when applying conven- tional kinetic-frictional closures to continuum modeling of high shear granulation (HSG), Conventional models refer to closure laws where the kinetic and frictional stresses are summed up to obtain the total stress field, In the simple, dense, and sheared system ofa Couette shear cell, the effect of the lack of scale separation on the model predictions is examined, both quantitatively and qualitatively. It is observed that the spatial resolution has a significant effect on the magnitude of the kinetic and frictional contributions to the solid phase stresses. With this new investigation and previous studies of HSG, it is concluded that conventional kinetic-frictional models are inadequate for continuum modeling of HSG.展开更多
The Eulerian-Eulerian framework was used in the numerical simulation of liquid hydrodynamics and particle motion in liquid-fluidized beds. The kinetic theory of granular flow, which accounts for the viscous drag influ...The Eulerian-Eulerian framework was used in the numerical simulation of liquid hydrodynamics and particle motion in liquid-fluidized beds. The kinetic theory of granular flow, which accounts for the viscous drag influence on the interstitial liquid phase, was used in combination with two-fluid models to simulate unsteady liquid-solid two-phase flows. We focus on local unsteady features predicted by the numerical models. The solid fraction power spectrum was analyzed. A typical flow pattern, such as core annular flow and particle back-mixing near the wall region of liquid-solid fluidized beds is obtained from this calculation. Effects of the restitution coefficient of particle-particle collisions on the distribution of granular pressure and temperature are discussed. Good agreement was achieved between the simulated results and experimental findings.展开更多
基金the financial support from the National Natural Science Foundation of China (22078058)Open Research Fund Program of CAS Key Laboratory of Energy Regulation Materials (ORFP2020–02)
文摘We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments,numerical predictions have been successfully used to explain the influences of impeller rotating speed,particle density, particle size, liquid viscosity and initial solid loading on the solid suspension behavior,i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed(N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine(RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.
基金funded by National Natural Science Foundation of China under the Grant No.51776059 and Key R&D Program of China Construction Second Engineering Bureau Co.Ltd.(Grant No.2021ZX180001).
文摘Hydrodynamics of carbon dioxide fluid-particle mixtures are predicted using a low density ratio-based kinetic theory of granular flow in high pressure carbon dioxide fluid fluidized beds.A coexistence of particle waves and particle aggregates exists along bed height.The threshold to identify the occurrence of particle aggregates is suggested based on standard deviation of solid volume fractions in aggregative fluidization.The existence time fractions and frequencies of particle aggregates are predicted along axial direction.The effect of carbon dioxide fluid temperature and pressure on volume fraction and velocity distributions are analyzed at different inlet carbon dioxide velocities and particle densities in high pressure carbon dioxide fluidized beds.Simulated results indicate that the carbon dioxide-particles fluidization transits from particulate to aggregative states with the increase of inlet carbon dioxide ve-locities.The computed fluid volume fractions and heterogeneity indexes are close to the measurements in a high pressure carbon dioxide fluidized bed.
文摘This paper presents a numerical and experimental study of the discharge rate of sawdust from an aerated hopper as an important parameter in many industrial processes involving the handling of other granular materials. Numerical experiments are conducted by means of an Eulerian-Eulerian approach coupled with the kinetic theory of granular flow (KTGF). Emphasis is given to the effects of particle size, hopper outlet width, hopper half angle, aeration height and air flow rate. The results show that the discharge rate is significantly affected by hopper outlet width, particle size and air flow rate, but is not sensitive to the hopper half angle and aeration height: increasing hopper outlet width or air flow rate increases discharge rate, while increasing particle size decreases discharge rate. Close agreement between numerical predictions and experimental results is obtained.
基金Financial support from Nanyang Technological University’s Start-up Grant (Grant No. SUG 8/07) is gratefully acknowledged
文摘The present work examines the predictive capability of a two-fluid CFD model that is based on the kinetic theory of granular flow in simulating dilute-phase turbulent liquid-particle pipe flows in which the inter- stitial fluid effect on the particle fluctuating motion is significant. The impacts of employing different drag correlations and turbulence closure models to describe the fluid-particle interactions (i.e. drag force and long-range interaction) are examined at both the mean and fluctuating velocity levels. The model pre- dictions are validated using experimental data of turbulent liquid-particle flows in a vertical pipe at different particle Reynolds numbers (Rep 〉 400 and Rep 〈 400), which characterize the importance of the vortex shedding phenomenon in the fluid-phase turbulence modulation. The results indicate that (1) the fluctuating velocity level predictions at different Rep are highly sensitive to the drag correlation selec- tion and (2) different turbulence closure models must be employed to accurately describe the long-range fluid-particle interaction in each phase. In general, good agreement is found between the model predic- tions and the experimental data at both the mean and fluctuating velocity levels provided that appropriate combinations of the drag correlation and the turbulence closure model are selected depending on Rep. 2009 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
文摘We present experimental investigations and numerical simulations of a pseudo-2D riser. Experiments were performed for various airflow rates, particle types/diameters, and particle size distributions. Pres- sure distributions along the wall of the riser were measured, Additional measurements from a smaller pseudo-2D riser (Kallio et al., 2009; Shah et al., 2012) were used to analyze horizontal solids volume fraction profiles. The experimental data were compared with simulation results carried out using an Euler-Euler approach, A mesh sensitivity study was conducted for numerical simulations and effects associated with simplifying real 3D geometry to a 2D model were examined. In addition, the effect of using an algebraic equation to represent the granular temperature versus a full partial differential equation also was examined for numerical simulations. Results showed small but significant near-wall sensitivity of the flow variables to mesh size. Substantial differences in mean pressure, solids distribution, and solid velocities were obtained, when 2D and 3D simulation results were compared. Finally, applying the simplified granular temperature equation for turbulent fluidization and for dilute-phase transport can lead to incorrect predictions in models,
文摘This short communication demonstrates why extreme caution has to be taken when applying conven- tional kinetic-frictional closures to continuum modeling of high shear granulation (HSG), Conventional models refer to closure laws where the kinetic and frictional stresses are summed up to obtain the total stress field, In the simple, dense, and sheared system ofa Couette shear cell, the effect of the lack of scale separation on the model predictions is examined, both quantitatively and qualitatively. It is observed that the spatial resolution has a significant effect on the magnitude of the kinetic and frictional contributions to the solid phase stresses. With this new investigation and previous studies of HSG, it is concluded that conventional kinetic-frictional models are inadequate for continuum modeling of HSG.
文摘The Eulerian-Eulerian framework was used in the numerical simulation of liquid hydrodynamics and particle motion in liquid-fluidized beds. The kinetic theory of granular flow, which accounts for the viscous drag influence on the interstitial liquid phase, was used in combination with two-fluid models to simulate unsteady liquid-solid two-phase flows. We focus on local unsteady features predicted by the numerical models. The solid fraction power spectrum was analyzed. A typical flow pattern, such as core annular flow and particle back-mixing near the wall region of liquid-solid fluidized beds is obtained from this calculation. Effects of the restitution coefficient of particle-particle collisions on the distribution of granular pressure and temperature are discussed. Good agreement was achieved between the simulated results and experimental findings.