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Sökning: WFRF:(Jonsson Pär) > Ni Peiyuan

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1.
  • Chen, Chao, et al. (författare)
  • A Model Study of Inclusions Deposition, Macroscopic Transport, and Dynamic Removal at Steel–Slag Interface for Different Tundish Designs
  • 2016
  • Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 47:3, s. 1916-1932
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents computational fluid dynamics (CFD) simulation results of inclusions macroscopic transport as well as dynamic removal in tundishes. A novel treatment was implemented using the deposition velocity calculated by a revised unified Eulerian deposition model to replace the widely used Stokes rising velocity in the boundary conditions for inclusions removal at the steel–slag interface in tundishes. In this study, the dynamic removal for different size groups of inclusions at different steel–slag interfaces (smooth or rough) with different absorption conditions at the interface (partially or fully absorbed) in two tundish designs was studied. The results showed that the dynamic removal ratios were higher for larger inclusions than for smaller inclusions. Besides, the dynamic removal ratio was higher for rough interfaces than for smooth interfaces. On the other hand, regarding the cases when inclusions are partially or fully absorbed at a smooth steel–slag interface, the removal ratio values are proportional to the absorption proportion of inclusions at the steel–slag interface. Furthermore, the removal of inclusions in two tundish designs, i.e., with and without a weir and a dam were compared. Specifically, the tundish with a weir and a dam exhibited a better performance with respect to the removal of bigger inclusions (radii of 5, 7, and 9 μm) than that of the case without weir and dam. That was found to be due to the strong paralleling flow near the middle part of the top surface. However, the tundish without weir and dam showed a higher removal ratio of smaller inclusions (radius of 1 μm). The reason could be the presence of a paralleling flow near the inlet zone, where the inclusions deposition velocities were much higher than in other parts.
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  • Ni, Peiyuan (författare)
  • A Study on Particle Motion and Deposition Rate : Application in Steel Flows
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Non-metallic inclusions in molten steel have received worldwide attention due to their serious influence on both the steel product quality and the steel production process. These inclusions may come from the de-oxidation process, the re-oxidation by air and/or slag due to an entrainment during steel transfer, and so on. The presence of some inclusion types can cause a termination of a casting process by clogging a nozzle. Thus, a good knowledge of the inclusion behavior and deposition rate in steel flows is really important to understand phenomena such as nozzle clogging. In this thesis, inclusion behaviors and deposition rates in steel flows were investigated by using mathematical simulations and validation by experiments.A ladle teeming process was simulated and Ce2O3 inclusion behavior during a teeming stage was studied. A Lagrangian method was used to track the inclusions in a steel flow and to compare the behaviors of inclusions of different sizes. In addition, a statistical analysis was conducted by the use of a stochastic turbulence model to investigate the behaviors of different-sized inclusions in different nozzle regions. The results show that inclusions with a diameter smaller than 20 μm were found to have similar trajectories and velocity distributions in the nozzle. The inertia force and buoyancy force were found to play an important role for the behavior of large-size inclusions or clusters. The statistical analysis results indicate that the region close to the connection region of the straight pipe and the expanding part of the nozzle seems to be very sensitive for an inclusion deposition.In order to know the deposition rate of non-metallic inclusions, an improved Eulerian particle deposition model was developed and subsequently used to predict the deposition rate of inclusions. It accounts for the differences in properties between air and liquid metals and considers Brownian and turbulent diffusion, turbophoresis and thermophoresis as transport mechanisms. A CFD model was firstly built up to obtain the friction velocity caused by a fluid flow. Then, the friction velocity was put into the deposition model to calculate the deposition rate.For  the  case  of  inclusion/particle  deposition  in  vertical  steel  flows,  effects  on  the deposition rate of parameters such as steel flow rate, particle diameter, particle density, wall roughness and temperature gradient near a wall were investigated. The results show that the steel flow rate/friction velocity has a very important influence on the rate of the deposition of large particles, for which turbophoresis is the main deposition mechanism. For small particles, both the wall roughness and thermophoresis have a significant influence on the particle deposition rate. The extended Eulerian model was thereafter used to predict the inclusion deposition rate in a submerged entry nozzle (SEN). Deposition rates of different-size inclusions in the SEN were obtained. The result shows that the steel flow is non-uniform in the SEN of the tundish. This leads to an uneven distribution of the inclusion deposition rates at different locations of the inner wall of the SEN. A large deposition rate was found to occur at the regions near the SEN inlet, the SEN bottom and the upper region of two SEN ports.For the case of an inclusion/particle deposition in horizontal straight channel flows, the deposition rates of particles at different locations of a horizontal straight pipe cross- section were found to be different due to the influence of gravity and buoyancy. For small particles with a small particle relaxation time, the gravity separation is important for their deposition  behaviors  at  high  and  low  parts  of  the  horizontal  pipe  compared  to  the turbophoresis. For large particles with a large particle relaxation time, turbophoresis is the dominating deposition mechanism. 
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4.
  • Ni, Peiyuan, 1987-, et al. (författare)
  • A study on the nonmetallic inclusion motions in a swirling flow submerged entry nozzle in a new cylindrical tundish design
  • 2018
  • Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 49:2, s. 723-736
  • Tidskriftsartikel (refereegranskat)abstract
    • Different sizes and shapes of nonmetallic inclusions in a swirling flow submerged entry nozzle (SEN) placed in a new tundish design were investigated by using a Lagrangian particle tracking scheme. The results show that inclusions in the current cylindrical tundish have difficulties remaining in the top tundish region, since a strong rotational steel flow exists in this region. This high rotational flow of 0.7 m/s provides the required momentum for the formation of a strong swirling flow inside the SEN. The results show that inclusions larger than 40 µm were found to deposit to a smaller extent on the SEN wall compared to smaller inclusions. The reason is that these large inclusions have Separation number values larger than 1. Thus, the swirling flow causes these large size inclusions to move toward the SEN center. For the nonspherical inclusions, large size inclusions were found to be deposited on the SEN wall to a larger extent, compared to spherical inclusions. More specifically, the difference of the deposited inclusion number is around 27 pct. Overall, it was found that the swirling flow contains three regions, namely, the isotropic core region, the anisotropic turbulence region and the near-wall region. Therefore, anisotropic turbulent fluctuations should be taken into account when the inclusion motion was tracked in this complex flow. In addition, many inclusions were found to deposit at the SEN inlet region. The plotted velocity distribution shows that the inlet flow is very chaotic. A high turbulent kinetic energy value of around 0.08 m2/s2 exists in this region, and a recirculating flow was also found here. These flow characteristics are harmful since they increase the inclusion transport toward the wall. Therefore, a new design of the SEN inlet should be developed in the future, with the aim to modify the inlet flow so that the inclusion deposition is reduced.
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5.
  • Ni, Peiyuan, et al. (författare)
  • Application of a swirling flow producer in a conventional tundish during continuous casting of steel
  • 2017
  • Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 57:12, s. 2175-2184
  • Tidskriftsartikel (refereegranskat)abstract
    • A swirling flow producer was designed for a conventional tundish in order to produce a swirling flow in the SEN driven by the steel flow potential. CFD simulations were carried out to investigate the flow phenomena in the new tundish system. The results show that a swirling flow in the tundish SEN was successfully obtained. The swirl number of the obtained steel flow inside the SEN can reach a value of 1.34, with a tangential velocity of around 2.8 m/s. The possibility of slag entrainment at the top of the tundish was estimated by analyzing the steel flow characteristics near the top surface. The calculated Weber Number is around 0.3 outside the cylinder, which indicates a low possibility of slag entrainment. A high value of shear stress was found on the SEN wall. This is due to the rotational steel flow in SEN. Also, non-metallic inclusions were tracked in the fully developed steel flow field. It was found that the number of inclusions that touch the top surface increases with an increased inclusion size. Small size inclusions mainly move into the cylinder from the left side of tangential inlet. Therefore, methods like installing a dam at the tundish bottom may be helpful to change the inclusion trajectories to move towards the top of the tundish.
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6.
  • Ni, Peiyuan, et al. (författare)
  • Deposition of particles in liquid flows in horizontal straight channels
  • 2016
  • Ingår i: International Journal of Heat and Fluid Flow. - : Elsevier. - 0142-727X .- 1879-2278. ; 62, s. 166-173
  • Tidskriftsartikel (refereegranskat)abstract
    • A flow in a horizontal channel is an important method for the transport of materials, products and/or waste gases/liquids. The deposition of particles in a horizontal channel may clog the flow path. The purpose of this paper is to extend the use of a developed Eulerian deposition model to liquid flows in horizontal straight channels to predict the particle deposition rate. For a horizontal pipe, the deposition rates may differ greatly along a cross section, due to the influences of gravity and buoyancy. The current deposition model is first applied to air flows to enable a comparison with available experimental data. Then, the model is applied to liquid flows in horizontal straight pipes. The effects of gravity, buoyancy, water flow rates, wall roughness, particle size and temperature difference in the near-wall boundary layer on the deposition rate have been studied and explained. The results show that the deposition rates of particles increase with an increased flow rate. The gravity separation has a large influence on the deposition of large particle at high and low parts of the horizontal pipe in some flows. Moreover, both the wall roughness and thermophoresis have a significant influence on the deposition rate of small particles. In addition, the roughness also shows an important influence on the large particle deposition at the top of the investigated pipe, due to that a large value of roughness can make the deposition location somewhat far away from the wall, where a stronger turbophoresis exists. The intensity of the turbophoresis relative to the gravity separation before a particle is reaching the deposition location is important for the large particle deposition when the gravity separation play a negative role on the deposition rate. (C) 2016 Elsevier Inc. All rights reserved.
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8.
  • Ni, Peiyuan, et al. (författare)
  • Non-Metallic Inclusion Behaviors in a New Tundish and SEN Design Using a Swirling Flow during Continuous Casting of Steel
  • 2016
  • Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X.
  • Tidskriftsartikel (refereegranskat)abstract
    • The behaviors of non-metallic inclusions in a new tundish and SEN design enabling a swirling flow are investigated by using a Lagrangian particle tracking scheme. The results show that 99% of both Al2O3 and Ce2O3 inclusions are removed from both the top surface and the other tundish walls with a "trap" boundary condition, while only around 60% are removed from the top surface of tundish for a "reflect" boundary condition at the other tundish walls. Large size non-metallic inclusions of different densities show a large difference under a "reflect" boundary condition at tundish walls, due to a high buoyancy of light inclusions. In the swirling flow SEN, a much smaller number of large Al2O3 inclusions touches the wall compared to Ce2O3 inclusions. This is due to that they have larger deviations from the steel flow path compared to heavy Ce2O3 inclusions, due to the centripetal force. For small size inclusions, the centripetal separation is not effective neither for the light Al2O3 inclusions nor for the heavy Ce2O3 inclusions in the current swirling flow SEN with a swirl number of 0.4. Light Al2O3 inclusions larger than 40μm can be influenced by the current centripetal force.
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9.
  • Ni, Peiyuan, 1987-, et al. (författare)
  • Numerical and Physical Study on a Cylindrical Tundish Design to Produce a Swirling Flow in the SEN During Continuous Casting of Steel
  • 2017
  • Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 48:5, s. 2695-2706
  • Tidskriftsartikel (refereegranskat)abstract
    • A new tundish design was investigated using both water model experiments and numerical simulations. The results show that the Reynolds Stress Model simulation results agree well with the Particle Image Velocimetry-measured results for water model experiments. A strong swirling flow in the Submerged Entry Nozzle (SEN) of the new tundish was successfully obtained, and the tangential velocity in the region near SEN inlet could reach a value of around 3.1 m/s. A high value of the shear stress was found to exist on the SEN wall, due to the strong swirling flow inside the SEN. This large shear stress leads to the dissipation of the rotational momentum of the steel flow. Thus, the maximum tangential velocity of the steel flow decreases from 3.1 m/s at around the SEN inlet to 2.2 m/s at a location close to the SEN outlet. In addition, the near-wall region has a high pressure, which is larger than the atmospheric pressure, due to the centrifugal effect. The calculated swirl number, with the value of around 1.6 at SEN inlet, illustrates that the current design can produce a similar strong swirling flow compared to the swirl blade method and the electromagnetic stirring method, while this is obtained by simply changing the steel flow path in tundish instead of using additional device to influence the flow.
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10.
  • Ni, Peiyuan (författare)
  • Numerical Study on Steel Flow and Inclusion Behavior during a Ladle Teeming Process
  • 2013
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Inclusions in molten steel have received worldwide concern due to their serious influence on both the steel product quality and the steel production process. These inclusions may come from the deoxidation process, reoxidation by air and/or slag due to an entrainment during steel transfer, and so on. They can break up a casting process by clogging a nozzle. A good knowledge on both steel flow and inclusion behavior is really important to understand nozzle clogging, as well as to take some possible measures to alleviate clogging. In this thesis, steel flow and inclusion behavior during a teeming process were investigated by mathematical simulations with verification by pilot-plant experiments.Firstly, steel flow phenomena during a ladle teeming process were studied. Different turbulence models, including the low Reynolds number k-ɛ model and the realizable k-ɛ model both with an enhanced wall treatment (EWT) and a standard wall function (SWF), were used to simulate this process. All of these turbulence model predictions generally agreed well with the experimental results. The velocity distributions in the nozzle were also predicted by these turbulence models. A large difference of the boundary-layer velocity predicted with these two near wall treatment methods was found. At the late stage of the teeming process, the drain sink flow phenomena were studied. The combination of an inclined ladle bottom and a gradually expanding nozzle was found to be an effective way to alleviate a drain sink flow during teeming.Then, inclusion behavior during a teeming stage was studied. A Lagranian method was used to track the inclusions in steel flow and compare the behaviors of different-size inclusions. In addition, a statistical analysis was conducted by the use of a stochastic turbulence model to investigate the behaviors of different-size inclusions in different nozzle regions. Inclusions with a diameter smaller than 20μm were found to have a similar trajectory and velocity distribution in the nozzle. However, inertia force and buoyancy force were found to play an important role for the behavior of large-size inclusions or clusters. The statistical analysis results indicate that the regions close to the connection between different angled nozzle parts seem to be very sensitive for an inclusion deposition.
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  • Resultat 1-10 av 17

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