A computational fluid dynamics （CFD） simulation was carried out with CFX4,3 to investigate the melt flow and temperature distributions in the settler of a flash furnace. Sixteen cases of one slag tap hole adopted wi...A computational fluid dynamics （CFD） simulation was carried out with CFX4,3 to investigate the melt flow and temperature distributions in the settler of a flash furnace. Sixteen cases of one slag tap hole adopted with one matte tap hole （1-to-l） and one slag tap hole adopted with two matte tap holes （1-to-2） operation modes were modelled. The simulation results show that the melt flows are similar in both two operation modes, but evident circulations can be found in the case of the 1-to-2 operation mode. The combination modes of the slag and matte tap holes are found to have a significant effect on the temperature distributions of the melt. The melt temperature is more uniform in the case of the 1-to-2 mode. Selection of a matte tap hole farther away from the inlet is more conducive to achieve a uniform distribution of the melt temperature in the settler in nractical tannine oneration展开更多
Primary dendrite arm spacing（PDAS） of α phase in directionally solidified Pb-26%Bi（mass fraction） hypo-peritectic alloys was measured by considering the effect of melt convection in cylindrical samples with diffe...Primary dendrite arm spacing（PDAS） of α phase in directionally solidified Pb-26%Bi（mass fraction） hypo-peritectic alloys was measured by considering the effect of melt convection in cylindrical samples with different diameters.The experimental results show the measured PDAS increases with increasing diameter of the sample.At the growth velocity of 5 μm/s,its value changes from 161.5 μm for the sample with 1.8 mm in diameter to 240.4 μm for the sample with 7 mm in diameter.The strong melt convection in large diameter samples causes a high bulk alloy composition and a high concentration gradient in peritectic β phase,resulting in a larger PDAS.Simultaneously,the high concentration gradient could effectively promote the peritectic transformation,enhancing the dissolution of the thin α dendrite.展开更多
Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)d...Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)during gas atomization(GA)process.The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN.With the decrease of the MDN inner-diameter,the melt flow resistance increased for both molten aluminum and iron,especially achieving an order of 10^(2) kPa in the case of the MDN inner-diameter≤1 mm.Based on the conventional GA process,the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN,thus producing powders under different MDN inner-diameters.When the MDN inner-diameter was reduced from 4 to 2 mm,the yield of fine powder(<150μm)soared from 54.7%to 94.2%.The surface quality of powders has also been improved when using a smaller inner-diameter MDN.展开更多
A collocated finite volume method on unstructured meshes is introduced to simulate the viscoelastic flow of the polymer melt with viscous dissipation past a confined cylinder.The constitutive equation for the simulati...A collocated finite volume method on unstructured meshes is introduced to simulate the viscoelastic flow of the polymer melt with viscous dissipation past a confined cylinder.The constitutive equation for the simulations is non-isothermal FENE-P model,which is derived from the molecular theories.The temperature effect on the macroscopic fields(e.g.,velocity,stress) and microscopic fields(e.g.,molecular orientation,deformation,stretch) is investigated by comparison of isothermal and non-isothermal situations.This investigation indicates that temperature rise caused by viscous dissipation should not be neglected since it has significant effect on the macroscopic and microscopic properties of the polymer melt.展开更多
The numerical model for predicting the flow and temperature fields of the melt in holding furnace with porous brick purging system were set up using Euler-Lagrange approach.In this model,bubbles coalescence and disint...The numerical model for predicting the flow and temperature fields of the melt in holding furnace with porous brick purging system were set up using Euler-Lagrange approach.In this model,bubbles coalescence and disintegration were ignored based on the dimensionless analysis,and the bubble size was assumed to be obedient to Rosin-Rammler distribution with a mean size of 0.6 mm.The results show that on reference operating condition,during the heating and agitation process,melt mixes well in the furnace,and the melt velocity increases with the increase of gas flux.Holding the melt for 30 min causes the max temperature in the bulk melt to increase to 60 K.After holding the heat,the agitation processing restarts,and it takes 10 min for the stratified melt to retrieve the homogeneous temperature field when the gas flux is 10 L/min,which shows deficient alloying and degassing in the melt.With the increase of gas flux from 10 to 20,30 and 40 L/min,the necessary recovery time decreases from 10 to 6,5 and 4 min gradually,which shows the improvement of the stirring efficiency.Depending on the processing purposes,for both good degassing performance and gas saving,proper operating strategy and parameters (gas flux,primarily) could be adjusted.展开更多
The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pu...The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260？？ under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and then it is substituted into the magnetic field model.The fluid flow model was solved with the acquired electromagnetic force.The effects of pulse voltage frequency on the current wave and on the distribution of magnetic and flow fields were numerically studied.The pulsed magnetic field increases melt convection,which stirs and fractures the dendritic arms into pieces.These broken pieces are transported into the bulk liquid by the liquid flow and act as nuclei to enhance grain refinement.The Joule heat effect produced by the electric current also participates in the microstructural refinement.展开更多
The simulation of three-dimensional （3D） non-isothermal, non-Newtonian fluid filling process is an extremely difficult task and remains a challenging problem, which includes polymer melt flow with free surface coupl...The simulation of three-dimensional （3D） non-isothermal, non-Newtonian fluid filling process is an extremely difficult task and remains a challenging problem, which includes polymer melt flow with free surface coupled with transient heat transfer. This paper presents a full 3D non-isothermal two-phase flow model to predict the complex flow in melt filling process, where the Cross-WLF model is applied to characterize the rheological behav- ior of polymer melt. The governing equations are solved using finite volume method with SIMPLEC algorithm on collocated grids and the melt front is accurately captured by a high resolution level set method. A domain exten- sion technique is adopted to deal with the complex cavities, which greatly reduces the computational burden. To verify the validity of the developed 3D approach, the melts filling processes in two thin rectangular cavities （one of them with a cylindrical insert） are simulated. The predicted melt front interfaces are in good agreement with the experiment and commercial software prediction. For a case with a rather complex cavity, the dynamic filling process in a hemispherical shell is successfully simulated. All of the numerical results show that the developed numerical procedure can provide a reasonable orediction for injection molding process.展开更多
The minimum fluid velocity to maintain particles just suspendedwas deduced, and the theoretical analysis shows that the minimumvelocity is influenced by the properties of the solid and liquid, notby the operational co...The minimum fluid velocity to maintain particles just suspendedwas deduced, and the theoretical analysis shows that the minimumvelocity is influenced by the properties of the solid and liquid, notby the operational conditions. For justification, the local minimumvelocity at the bottom of the tank was measured by a bi- electrodeconductivity probe, in a square-sectioned stirred tank (0.75m×0.75×1.0m) with the glass beads-water system. The experiments showed thatthe fluid velocities for the same suspension state were identicaldespite that the power Dissipated per unite mass was not the sameunder different configuration and operation. Both theoreticalanalysis And experimental results indicate that the off-bottomsuspension is controlled by the local fluid flow over the bottom Ofthe stirred tank.展开更多
基金Project (2002AA00104) supported by the National High-tech Research and Development Program of China
文摘A computational fluid dynamics （CFD） simulation was carried out with CFX4,3 to investigate the melt flow and temperature distributions in the settler of a flash furnace. Sixteen cases of one slag tap hole adopted with one matte tap hole （1-to-l） and one slag tap hole adopted with two matte tap holes （1-to-2） operation modes were modelled. The simulation results show that the melt flows are similar in both two operation modes, but evident circulations can be found in the case of the 1-to-2 operation mode. The combination modes of the slag and matte tap holes are found to have a significant effect on the temperature distributions of the melt. The melt temperature is more uniform in the case of the 1-to-2 mode. Selection of a matte tap hole farther away from the inlet is more conducive to achieve a uniform distribution of the melt temperature in the settler in nractical tannine oneration
基金Project(50395100)supported by the National Natural Science Foundation of ChinaProject(NCET-07-0692)supported by the New Century Talents Program of the Ministry of Education,ChinaProject(34-TP-2009)supported by Open Project of State Key Laboratory of Solidification Processing,China
文摘Primary dendrite arm spacing（PDAS） of α phase in directionally solidified Pb-26%Bi（mass fraction） hypo-peritectic alloys was measured by considering the effect of melt convection in cylindrical samples with different diameters.The experimental results show the measured PDAS increases with increasing diameter of the sample.At the growth velocity of 5 μm/s,its value changes from 161.5 μm for the sample with 1.8 mm in diameter to 240.4 μm for the sample with 7 mm in diameter.The strong melt convection in large diameter samples causes a high bulk alloy composition and a high concentration gradient in peritectic β phase,resulting in a larger PDAS.Simultaneously,the high concentration gradient could effectively promote the peritectic transformation,enhancing the dissolution of the thin α dendrite.
基金the National Natural Science Foundation of China(No.52074157)Shenzhen Science and Technology Innovation Com-mission,China(Nos.JSGG20180508152608855,KQTD20170328154443162)Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials,China(No.ZDSYS201703031748354).
文摘Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)during gas atomization(GA)process.The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN.With the decrease of the MDN inner-diameter,the melt flow resistance increased for both molten aluminum and iron,especially achieving an order of 10^(2) kPa in the case of the MDN inner-diameter≤1 mm.Based on the conventional GA process,the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN,thus producing powders under different MDN inner-diameters.When the MDN inner-diameter was reduced from 4 to 2 mm,the yield of fine powder(<150μm)soared from 54.7%to 94.2%.The surface quality of powders has also been improved when using a smaller inner-diameter MDN.
基金Supported by the National Natural Science Foundation of China（10590353 10871159） the National Basic Research Program of China（2005CB321704） the Doctoral Foundation of Northwestern Polytechnical University（CX200817）
文摘A collocated finite volume method on unstructured meshes is introduced to simulate the viscoelastic flow of the polymer melt with viscous dissipation past a confined cylinder.The constitutive equation for the simulations is non-isothermal FENE-P model,which is derived from the molecular theories.The temperature effect on the macroscopic fields(e.g.,velocity,stress) and microscopic fields(e.g.,molecular orientation,deformation,stretch) is investigated by comparison of isothermal and non-isothermal situations.This investigation indicates that temperature rise caused by viscous dissipation should not be neglected since it has significant effect on the macroscopic and microscopic properties of the polymer melt.
基金Project(2008AA11A116) supported by the National High Technology Research and Development Program of China
文摘The numerical model for predicting the flow and temperature fields of the melt in holding furnace with porous brick purging system were set up using Euler-Lagrange approach.In this model,bubbles coalescence and disintegration were ignored based on the dimensionless analysis,and the bubble size was assumed to be obedient to Rosin-Rammler distribution with a mean size of 0.6 mm.The results show that on reference operating condition,during the heating and agitation process,melt mixes well in the furnace,and the melt velocity increases with the increase of gas flux.Holding the melt for 30 min causes the max temperature in the bulk melt to increase to 60 K.After holding the heat,the agitation processing restarts,and it takes 10 min for the stratified melt to retrieve the homogeneous temperature field when the gas flux is 10 L/min,which shows deficient alloying and degassing in the melt.With the increase of gas flux from 10 to 20,30 and 40 L/min,the necessary recovery time decreases from 10 to 6,5 and 4 min gradually,which shows the improvement of the stirring efficiency.Depending on the processing purposes,for both good degassing performance and gas saving,proper operating strategy and parameters (gas flux,primarily) could be adjusted.
基金Project(50774075)supported by the National Natural Science Foundation of ChinaProject(2006BAE04B01-4)supported by Key Technologies R&D Program,China
文摘The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260？？ under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and then it is substituted into the magnetic field model.The fluid flow model was solved with the acquired electromagnetic force.The effects of pulse voltage frequency on the current wave and on the distribution of magnetic and flow fields were numerically studied.The pulsed magnetic field increases melt convection,which stirs and fractures the dendritic arms into pieces.These broken pieces are transported into the bulk liquid by the liquid flow and act as nuclei to enhance grain refinement.The Joule heat effect produced by the electric current also participates in the microstructural refinement.
基金Supported by the National Basic Research Program of China(2012CB025903)the National Natural Science Foundation of China(91434201,11402210)
文摘The simulation of three-dimensional （3D） non-isothermal, non-Newtonian fluid filling process is an extremely difficult task and remains a challenging problem, which includes polymer melt flow with free surface coupled with transient heat transfer. This paper presents a full 3D non-isothermal two-phase flow model to predict the complex flow in melt filling process, where the Cross-WLF model is applied to characterize the rheological behav- ior of polymer melt. The governing equations are solved using finite volume method with SIMPLEC algorithm on collocated grids and the melt front is accurately captured by a high resolution level set method. A domain exten- sion technique is adopted to deal with the complex cavities, which greatly reduces the computational burden. To verify the validity of the developed 3D approach, the melts filling processes in two thin rectangular cavities （one of them with a cylindrical insert） are simulated. The predicted melt front interfaces are in good agreement with the experiment and commercial software prediction. For a case with a rather complex cavity, the dynamic filling process in a hemispherical shell is successfully simulated. All of the numerical results show that the developed numerical procedure can provide a reasonable orediction for injection molding process.
文摘The minimum fluid velocity to maintain particles just suspendedwas deduced, and the theoretical analysis shows that the minimumvelocity is influenced by the properties of the solid and liquid, notby the operational conditions. For justification, the local minimumvelocity at the bottom of the tank was measured by a bi- electrodeconductivity probe, in a square-sectioned stirred tank (0.75m×0.75×1.0m) with the glass beads-water system. The experiments showed thatthe fluid velocities for the same suspension state were identicaldespite that the power Dissipated per unite mass was not the sameunder different configuration and operation. Both theoreticalanalysis And experimental results indicate that the off-bottomsuspension is controlled by the local fluid flow over the bottom Ofthe stirred tank.
