Fluid flow characteristics in a four-strand tundish with gas blowing were studied by water modeling experiments.It is found that gas blowing can greatly improve the flow characteristics in the tundish with a turbulenc...Fluid flow characteristics in a four-strand tundish with gas blowing were studied by water modeling experiments.It is found that gas blowing can greatly improve the flow characteristics in the tundish with a turbulence inhibitor.It dramatically increases the peak concentration time,and greatly decreases the dead volume,and reduces the minimum residence time.The gas blowing location,gas flow rate,and porous plug area greatly influence the flow characteristics in the tundish; the gas blowing location near the baffle,smaller gas flow rate,and smaller porous plug area are better for improving the fluid flow characteristics.Using gas blowing can reduce the difference of flows at the middle outlets and side outlets for the multi-strand tundish.Bubbles produced by gas blowing can absorb small inclusions and provide the condition for inclusion collision and aggregation.Therefore,introducing gas blowing into a tundish and combining the turbulence inhibitor can improve inclusion floating and removal,and the cleanness of molten steel can be advanced.展开更多
The geological hazards, such as water inrush and mud outburst, are easily induced by the high water pressure caverns ahead of a karst tunnel face. Therefore, it is a pivotal issue to determine the reserved thickness o...The geological hazards, such as water inrush and mud outburst, are easily induced by the high water pressure caverns ahead of a karst tunnel face. Therefore, it is a pivotal issue to determine the reserved thickness of rock plug during the construction of tunnels. The limit analysis principle is employed to analyze the safe thickness from the point of energy dissipation, and the nonlinear and non-associated characteristics of geotechnical materials are both considered. On the basis of a plane failure pattern of rock plug, the expressions of detaching curve and rock plug thickness are derived. The effect of each parameter on the safe thickness of rock plug is discussed in detail, which interprets the corresponding failure scope of rock plug. The obtained results indicate that the thickness of rock plug is highly influenced by the nonlinear dilatancy coefficient and the nonlinear coefficient. The proposed method is validated by a comparison of the calculated results with those of the engineering project of the "526 karst cavern" of Yunwushan tunnel. This proposed method can provide reference basis for the design and excavation of karst tunnels in the future.展开更多
In the context of a sudden contraction plug conduit,the near-wall area experiences a significant shearing effect of water flow,however,the extent to which this shearing effect occurs in bubble-water flow and the relat...In the context of a sudden contraction plug conduit,the near-wall area experiences a significant shearing effect of water flow,however,the extent to which this shearing effect occurs in bubble-water flow and the related variation mechanisms of air bubble size and number remain unclear.This study employs a model test method to investigate the diffusion process of bubble-water flow in a sudden contraction plug conduit.The size and number of bubbles,as well as their distribution along the shearing section under varying initial air volume conditions,are studied in detail using a high-speed image acquisition system.The experimental findings reveal a self-similar relationship between the number and size of bubbles and their cross-sectional distribution over time.The bubble number and size vary in three stages,i.e.,quasi-suspension,shearing,and shearing completion stages.The direction perpendicular to the conduit exhibits peak values in bubble number distribution over the three stages,with peak value location varying with the near-wall area.As time progresses,the peak value increases,and a larger initial air volume corresponds to a smaller distance of the peak value location from the wall.The size of air bubbles near the wall is consistent with the minimum diameter of air bubbles in shear flow and is hardly affected by the initial air volume.These results aid in comprehending the change law of two-phase water and air flow under a strong shearing effect in the plug conduit,and provide useful insights for hydraulic design in fluid engineering.展开更多
文摘Fluid flow characteristics in a four-strand tundish with gas blowing were studied by water modeling experiments.It is found that gas blowing can greatly improve the flow characteristics in the tundish with a turbulence inhibitor.It dramatically increases the peak concentration time,and greatly decreases the dead volume,and reduces the minimum residence time.The gas blowing location,gas flow rate,and porous plug area greatly influence the flow characteristics in the tundish; the gas blowing location near the baffle,smaller gas flow rate,and smaller porous plug area are better for improving the fluid flow characteristics.Using gas blowing can reduce the difference of flows at the middle outlets and side outlets for the multi-strand tundish.Bubbles produced by gas blowing can absorb small inclusions and provide the condition for inclusion collision and aggregation.Therefore,introducing gas blowing into a tundish and combining the turbulence inhibitor can improve inclusion floating and removal,and the cleanness of molten steel can be advanced.
基金Project(2013CB036004) supported by the National Basic Research Program of ChinaProjects(51378510,51308072) supported by National Natural Science Foundation of ChinaProject(CX2014B069) supported by the Hunan Provincial Innovation Foundation for Postgraduate,China
文摘The geological hazards, such as water inrush and mud outburst, are easily induced by the high water pressure caverns ahead of a karst tunnel face. Therefore, it is a pivotal issue to determine the reserved thickness of rock plug during the construction of tunnels. The limit analysis principle is employed to analyze the safe thickness from the point of energy dissipation, and the nonlinear and non-associated characteristics of geotechnical materials are both considered. On the basis of a plane failure pattern of rock plug, the expressions of detaching curve and rock plug thickness are derived. The effect of each parameter on the safe thickness of rock plug is discussed in detail, which interprets the corresponding failure scope of rock plug. The obtained results indicate that the thickness of rock plug is highly influenced by the nonlinear dilatancy coefficient and the nonlinear coefficient. The proposed method is validated by a comparison of the calculated results with those of the engineering project of the "526 karst cavern" of Yunwushan tunnel. This proposed method can provide reference basis for the design and excavation of karst tunnels in the future.
基金supported by the National Natural Science Foundation of China(Grant Nos.52192673,51979182).
文摘In the context of a sudden contraction plug conduit,the near-wall area experiences a significant shearing effect of water flow,however,the extent to which this shearing effect occurs in bubble-water flow and the related variation mechanisms of air bubble size and number remain unclear.This study employs a model test method to investigate the diffusion process of bubble-water flow in a sudden contraction plug conduit.The size and number of bubbles,as well as their distribution along the shearing section under varying initial air volume conditions,are studied in detail using a high-speed image acquisition system.The experimental findings reveal a self-similar relationship between the number and size of bubbles and their cross-sectional distribution over time.The bubble number and size vary in three stages,i.e.,quasi-suspension,shearing,and shearing completion stages.The direction perpendicular to the conduit exhibits peak values in bubble number distribution over the three stages,with peak value location varying with the near-wall area.As time progresses,the peak value increases,and a larger initial air volume corresponds to a smaller distance of the peak value location from the wall.The size of air bubbles near the wall is consistent with the minimum diameter of air bubbles in shear flow and is hardly affected by the initial air volume.These results aid in comprehending the change law of two-phase water and air flow under a strong shearing effect in the plug conduit,and provide useful insights for hydraulic design in fluid engineering.
