Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions...Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank.Influences of operating conditions and physical properties of particles(i.e., particle diameter and density) on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied.The wide distribution of particle angular velocity ranging from 0 to 105r·min 1is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.展开更多
We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel....We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel.By adjusting the amplitude ratio and the phase difference between the two speakers,a plane traveling sound wave field can be achieved in the test section of the tunnel,which we checked by measuring the amplitudes and phases of the sound pressure along the tunnel and by simultaneously measuring the velocity field of the air flow at three different locations in the tunnel.When a liquid droplet was introduced in the test section,the motion of the droplet and the velocity of the air flow around the droplet were recorded by high speed cameras,from which we analyze and obtain the ratio of the velocity amplitudes and the phase difference between the particle motion and the fluid motion.The experimental data confirm the theoretical result from the wave equations in the long-wavelength regime,i.e.,when the particle size is much smaller than the wavelength.Moreover,we showed that in this regime,the theory on particle motion in an unsteady uniform fluid,when the history term is included,also yields the same results that are in agreement with the experimental data and the wave equation.Our result extends the parameter range over which the theory on particle motion in unsteady fluid is checked against experiments,especially to the range of particle-fluid density ratio that is of important practical applications.展开更多
基金Supported by the State Key Development Program for Basic Research of China （2013CB733600）, the National Natural Science Foundation of China （21036003, 20776074） and the Specialized Research Fund for the Doctoral Program of Higher Education of China （20090002110069）.
文摘Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank.Influences of operating conditions and physical properties of particles(i.e., particle diameter and density) on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied.The wide distribution of particle angular velocity ranging from 0 to 105r·min 1is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.
基金This work was supported partially by the National Natural Science Foundation of China(Grant No.11988102)and by Tsinghua University.
文摘We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel.By adjusting the amplitude ratio and the phase difference between the two speakers,a plane traveling sound wave field can be achieved in the test section of the tunnel,which we checked by measuring the amplitudes and phases of the sound pressure along the tunnel and by simultaneously measuring the velocity field of the air flow at three different locations in the tunnel.When a liquid droplet was introduced in the test section,the motion of the droplet and the velocity of the air flow around the droplet were recorded by high speed cameras,from which we analyze and obtain the ratio of the velocity amplitudes and the phase difference between the particle motion and the fluid motion.The experimental data confirm the theoretical result from the wave equations in the long-wavelength regime,i.e.,when the particle size is much smaller than the wavelength.Moreover,we showed that in this regime,the theory on particle motion in an unsteady uniform fluid,when the history term is included,also yields the same results that are in agreement with the experimental data and the wave equation.Our result extends the parameter range over which the theory on particle motion in unsteady fluid is checked against experiments,especially to the range of particle-fluid density ratio that is of important practical applications.
