The plasma status of vacuum arc before arc current zero,has a great influence on the interruption performance of the vacuum circuit breakers.In this paper,a vacuum arc model in a short gap was established based on the...The plasma status of vacuum arc before arc current zero,has a great influence on the interruption performance of the vacuum circuit breakers.In this paper,a vacuum arc model in a short gap was established based on the magnet hydrodynamic(MHD) and a common computational fluid dynamics(CFD) software was utilized to specially investigate the properties of this arc.The spatial distributions of plasma pressure,plasma density,ion axial velocity, and axial current density in front of the anode surface of vacuum arc in this case were obtained.Simulation results indicate that:from the cathode to the anode,both of the plasma pressure and the plasma density increase gradually,and the plasma axial velocity decreases gradually;the axial current density in front of anode has a large radial gradient, and the maximum value is still smaller than the threshold current density for the anode-spot formation,thus,the anode is still passive.The comparison between the plasma density of simulation and the CMOS images taken by the high-speed camera indicates that they are in reasonable agreement with each other and demonstrates the feasibility of the vacuum arc model.展开更多
This work focuses on the hydrodynamic behavior of admixtures of Geldart-B magnetizable and non- magnetizable particles in a magnetized fluidized bed. The applied magnetic field was axial, uniform, and steady. In opera...This work focuses on the hydrodynamic behavior of admixtures of Geldart-B magnetizable and non- magnetizable particles in a magnetized fluidized bed. The applied magnetic field was axial, uniform, and steady. In operating the beds, the magnetization-LAST mode was adopted under which four distinct flow regimes exist： fixed, magnetized-bubbling, partial segregation-bubbling, and total segregation-bubbling, The operational phase diagram was drawn to display the transitions between flow regimes in an intuitive manner. Only in the magnetized-bubbling regime could the magnetic field reduce the bubble size and improve fluidization quality. In the segregation-bubbling regimes, fluidization quality deteriorated as segregation developed. The segregation of the binary mixture was quantitatively studied by observing pressure drops in the local bed. Reasons for the improvement in fluidization quality as well as the occur- rence of segregation were analyzed. Furthermore. the flow regime transition under magnetization-LAST operation mode was different from that under magnetization-FIRST mode. The magnetically stabilized bed （MSB） flow regime, which could be easily created under magnetization-FIRST mode, could no longer be achieved under magnetization-LAST mode. With the admixture, the MSB was proved to be a metastable equilibrium state. Under the magnetization-LAST mode, the admixture bed reached directly the stable equilibrium state-bubbling with segregation.展开更多
基金Supported by National Natural Science Foundation of China(50537010,50977004)
文摘The plasma status of vacuum arc before arc current zero,has a great influence on the interruption performance of the vacuum circuit breakers.In this paper,a vacuum arc model in a short gap was established based on the magnet hydrodynamic(MHD) and a common computational fluid dynamics(CFD) software was utilized to specially investigate the properties of this arc.The spatial distributions of plasma pressure,plasma density,ion axial velocity, and axial current density in front of the anode surface of vacuum arc in this case were obtained.Simulation results indicate that:from the cathode to the anode,both of the plasma pressure and the plasma density increase gradually,and the plasma axial velocity decreases gradually;the axial current density in front of anode has a large radial gradient, and the maximum value is still smaller than the threshold current density for the anode-spot formation,thus,the anode is still passive.The comparison between the plasma density of simulation and the CMOS images taken by the high-speed camera indicates that they are in reasonable agreement with each other and demonstrates the feasibility of the vacuum arc model.
文摘This work focuses on the hydrodynamic behavior of admixtures of Geldart-B magnetizable and non- magnetizable particles in a magnetized fluidized bed. The applied magnetic field was axial, uniform, and steady. In operating the beds, the magnetization-LAST mode was adopted under which four distinct flow regimes exist： fixed, magnetized-bubbling, partial segregation-bubbling, and total segregation-bubbling, The operational phase diagram was drawn to display the transitions between flow regimes in an intuitive manner. Only in the magnetized-bubbling regime could the magnetic field reduce the bubble size and improve fluidization quality. In the segregation-bubbling regimes, fluidization quality deteriorated as segregation developed. The segregation of the binary mixture was quantitatively studied by observing pressure drops in the local bed. Reasons for the improvement in fluidization quality as well as the occur- rence of segregation were analyzed. Furthermore. the flow regime transition under magnetization-LAST operation mode was different from that under magnetization-FIRST mode. The magnetically stabilized bed （MSB） flow regime, which could be easily created under magnetization-FIRST mode, could no longer be achieved under magnetization-LAST mode. With the admixture, the MSB was proved to be a metastable equilibrium state. Under the magnetization-LAST mode, the admixture bed reached directly the stable equilibrium state-bubbling with segregation.
