BACKGROUND Inflammatory bowel disease(IBD)is a common chronic intestinal inflammatory disease.High oxidative stress is a treatment target for IBD.Cerium oxide(CeO2)nanomaterials as nanozymes with antioxidant activity ...BACKGROUND Inflammatory bowel disease(IBD)is a common chronic intestinal inflammatory disease.High oxidative stress is a treatment target for IBD.Cerium oxide(CeO2)nanomaterials as nanozymes with antioxidant activity are potential drugs for the treatment of colitis.AIM To synthesize hollow cerium(H-CeO2)nanoparticles by one-step method and to validate the therapeutic efficacy of H-CeO2 in IBD.METHODS H-CeO2 was synthesized by one-step method and examined its characterization and nanoenzymatic activity.Subsequently,we constructed dextran sulfate so-dium(DSS)-induced colitis in mice to observe the effects of H-CeO2 on colonic inflammation.The effects of H-CeO2 on colon inflammation and reactive oxygen species(ROS)levels in IBD mice were detected by hematoxylin and eosin staining and dichlorofluorescein diacetate staining,respectively.Finally,the biological sa-fety of H-CeO2 on mice was evaluated by hematoxylin and eosin staining,blood routine,and blood biochemistry.RESULTS H-CeO2 nanoparticles prepared by the one-step method were uniform,monodi-sperse and hollow.H-CeO2 had a good ability to scavenge ROS,∙OH and∙OOH.H-CeO2 reduced DSS-induced decreases in body weight and colon length,colonic epithelial damage,inflammatory infiltration,and ROS accumulation.H-CeO2 administration reduced the disease activity index of DSS-induced animals from about 8 to 5.H-CeO2 had no significant effect on body weight,total platelet count,hemoglobin,white blood cell,and red blood cell counts in healthy mice.No significant damage to major organs was observed in healthy mice following H-CeO2 administration.CONCLUSION The one-step synthesis of H-CeO2 nanomaterials had good antioxidant activity,biosafety,and inhibited deve-lopment of DSS-induced IBD in mice by scavenging ROS.展开更多
Rheocasting with semi-solid slurry has been widely used in industrial processes in recent years.The Cup-Cast method is one of the most effective ways to produce semi-solid slurry for rheocasting.In order to study the ...Rheocasting with semi-solid slurry has been widely used in industrial processes in recent years.The Cup-Cast method is one of the most effective ways to produce semi-solid slurry for rheocasting.In order to study the effect of electromagnetic stirring on the fabrication of semi-solid slurry,we have applied the Double-Axis-Electromagnetic Stirrer(DAEMS)to the Cup-Cast method.Microstructure of the slurry was observed by an optical microscope and Electron Back-Scatter Patterns(EBSP).The results indicated that the electromagnetic stirrer made it possible to accelerate the cooling rate of the melt,thus resulting in a higher quality slurry.展开更多
The three-dimensional(3D) Pd-based nanoflower structures,assembled from two-dimensional(2D)nanosheets,are characterized by their stable and ordered configurations.These structures have been extensively designed as ano...The three-dimensional(3D) Pd-based nanoflower structures,assembled from two-dimensional(2D)nanosheets,are characterized by their stable and ordered configurations.These structures have been extensively designed as anode materials for fuel cells.However,the exploration of trimetallic nanoflowers with porous architectures remains limited.In this study,we present a straightforward one-step solvothermal method for the synthesis of trimetallic Pd Cu Ni porous nanoflowers(PNFs).Leveraging several unique advantages,such as an open superstructure,high porosity,and enhanced electronic interactions among the trimetals,the resulting Pd Cu Ni PNFs demonstrate significantly improved electrochemical performance,with mass activities reaching 5.94 and 10.14 A/mg for the ethanol oxidation reaction(EOR)and the ethylene glycol oxidation reaction(EGOR),respectively.Furthermore,the Pd Cu Ni PNFs exhibit optimized d-band centers and the most negative onset oxidation potential,indicating enhanced antitoxicity and stability.This study not only provides a novel perspective on the synthesis of 3D porous nanomaterials but also highlights the potential application value of trimetallic nanoalloys in catalysis.展开更多
This work examines the microstructure and corrosion properties of fine-grained Al 7075 across different regions under varying cooling conditions during friction stir welding.The findings demonstrate that forced coolin...This work examines the microstructure and corrosion properties of fine-grained Al 7075 across different regions under varying cooling conditions during friction stir welding.The findings demonstrate that forced cooling significantly improves the corrosion resistance of the welded joints.Specifically,the corrosion resistance was the highest in the stir zone,followed by the thermo-mechanical affected zone,and then the heat affected zone.Forced cooling mitigates grain growth by controlling the welding thermal effects,thereby increasing the proportion ofΣ3 grain boundaries.The modification of these microstructural characteristics promotes the formation of a dense oxide layer,thereby enhancing the corrosion resistance.Furthermore,forced cooling mitigates the precipitation and coarsening of the anodic phase in the stir zone,which in turn reduces the susceptibility of the joint to pitting corrosion.Additionally,the lower recrystallization texture content in the joint,resulting from forced cooling,contributes to a reduction in the number of corrosion-active sites,thereby further improving the corrosion performance of the welded joint.展开更多
The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures...The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures were compared under mold electromagnetic stirring （MEMS） conditions （current of 300 A and frequency of 3 Hz）. Thereafter, the solidification structures of the large round billet were investigated under different superheats, casting speeds, and secondary cooling intensities. Finally, the effect of the MEMS current on the solidification structures was obtained under fixed superheat, casting speed, secondary cooling intensity, and MEMS frequency. The model accurately simulated the actual solidification structures of any steel, regardless of its size and the parameters used in the continuous casting process. The ratio of the central equiaxed grain zone was found to increase with decreasing superheat, increasing casting speed, decreasing secondary cooling intensity, and increasing MEMS current. The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.展开更多
In modern continuous casting of round steel blooms rotating electromagnetic fields are commonly employed to improve the product quality.Mould-electromagnetic stirrers(M-EMS)are used to excite a rotary motion along the...In modern continuous casting of round steel blooms rotating electromagnetic fields are commonly employed to improve the product quality.Mould-electromagnetic stirrers(M-EMS)are used to excite a rotary motion along the solidification front in the liquid core.These velocities lead to a better strand surface quality as well as enhancing the transition from columnar to equiaxed solidification.Although the usage of electromagnetic stirrers is widespread,not all effects are fully known or understood.Due to harsh conditions at the plant,measurements are scarce and limited.Water model experiments-an established alternative for investigating continuous casting of steel-cannot be used due to the low electrical conductivity of water.Experiments with liquid metals like mercury,Galinstan or Wood’s metal are either expensive or difficult to perform.Thus numeric simulations are essential to gain a better understanding of the processes involved in continuous casting with electromagnetic stirring.However numeric simulations should always be validated with experiments and/or measurements.While the velocity field inside the liquid core of the bloom cannot be measured at the caster,the velocity at the mould level can be measured by dipping a nail into it.The skull forming at the tip of the nail is directly linked to the occurring surface velocity.These measurements can then be compared with numeric simulations of the nail dipping process.The numeric model is restricted to the upper part of the strand.The lower part of the strand is also taken into account through adjusted boundary conditions(velocity field etc.taken from a simulation of the whole strand).In this work the influence of the stirring field strength on the simulation results will be investigated.In the future these nail dipping simulations will be validated with plant measurements.This can then to a certain extentvalidate the simulation of the strand with M-EMS too,as it serves as the basis for the nail dipping model.展开更多
Gradiently denitrated gun propellant(GDGP)prepared by a“gradient denitration”strategy is obviously superior in progressive burning performance to the traditional deterred gun propellant.Currently,the preparation of ...Gradiently denitrated gun propellant(GDGP)prepared by a“gradient denitration”strategy is obviously superior in progressive burning performance to the traditional deterred gun propellant.Currently,the preparation of GDGP employed a tedious two-step method involving organic solvents,which hinders the large-scale preparation of GDGP.In this paper,GDGP was successfully prepared via a novelty and environmentally friendly one-step method.The obtained samples were characterized by FT-IR,Raman,SEM and XPS.The results showed that the content of nitrate groups gradiently increased from the surface to the core in the surface layer of GDGP and the surface layer of GDGP exhibited a higher compaction than that of raw gun propellant,with a well-preserved nitrocellulose structure.The denitration process enabled the propellant surface with regressive energy density and good progressive burning performance,as confirmed by oxygen bomb and closed bomb test.At the same time,the effects of different solvents on the component loss of propellant were compared.The result showed that water caused the least component loss.Finally,the stability of GDGP was confirmed by methyl-violet test.This work not only provided environmentally friendly,simple and economic preparation of GDGP,but also confirmed the stability of GDGP prepared by this method.展开更多
Aimed at the problem of short life of mixing head in KR mechanical mixing method for desulfurization of hot metal,a new type of mixing stir was proposed.CFD theory was used to simulate the characteristics of the fluid...Aimed at the problem of short life of mixing head in KR mechanical mixing method for desulfurization of hot metal,a new type of mixing stir was proposed.CFD theory was used to simulate the characteristics of the fluid flow for the new type of stirring vessel of water model for KR mechanical desulfurization.Flow characteristics and structures of the flow field were investigated and compared with the traditional cross-flow type.The results show that the new type of impeller can not only improve the defects of the flow caused by stir structure of the traditional type,but also reduce the separation of mixing zone in the stirred tank and make the flow field more uniform to make the desulfurization more fully, thus shortening the mixing time,and improving the life of mixing head.Numerical simulation method has been proven to be sound by comparing with the experimental ones.展开更多
Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotatio...Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotational speed,welding speed,and tool tilt angle play a major role in deciding the joint characteristics.The joints fabricated using tapered square pin profile tool with a tool rotational speed of600r/min,welding speed of65mm/min,and tool tilt angle of1.5°result in an unexpected weld efficiency of93.51%.Mathematical models are developed to map the correlation between the parameters and responses(ultimate tensile strength and elongation)and these models are optimized to maximize the ultimate tensile strength of the friction stir welded joint.Response plots generated from the mathematical models are used to interpret the interaction effects of the welding parameters on the response variables.Adequacy of the developed models is validated using analysis of variance(ANOVA)technique.Results from the confirmatory experiments plotted in scatter diagram show a good agreement with predicted models.Different grain structures in various zones of the weld are examined by observing the micro and macro structures of the weld.展开更多
This paper presents a new idea about desulfurization with in-situ mechanical stirring method on the basis of desulfurization by single blow grain magnesium and KR method, that is, the inner gases carry the magnesium v...This paper presents a new idea about desulfurization with in-situ mechanical stirring method on the basis of desulfurization by single blow grain magnesium and KR method, that is, the inner gases carry the magnesium vapor formed in-site in molten iron by magnesium-based desulfurization, and bubble dispersed and disintegrated under the condition of mechanical stirring, thence to improve the efficiency of desulfurization by single blow grain magnesium .It has been proved by research of cold water model experiment that the bubble dispersion and disintegration can not only improve the desulphurization efficiency but also increase the utilization rate of magnesium. Obviously, the bubble dispersion and disintegration of magnesium vapor is the key problem in improving the desulphurization efficiency and increasing the utilization rate of magnesium. Thus the research focus on exploring the performance of bubble dispersion and disintegration on the base of refining process and gas-liquid mass transfer. According to the literature and cold water model experimental result basing on principle of similitude, the influencing factors and interaction of bubble dispersion and disintegration have been studied from the perspectives of physical and numerical simulation. The study would provide the theoretical and experimental data for the new method of desulfurization with in-situ mechanical stirring.展开更多
In this paper, a new computational method for improving the accuracy of numerically computed solutions is introduced. The computational method is based on the one-step method and conserved quantities of holonomic syst...In this paper, a new computational method for improving the accuracy of numerically computed solutions is introduced. The computational method is based on the one-step method and conserved quantities of holonomic systems are considered as kinematical constraints in this method.展开更多
A volume averaged columnar solidification model,which couples the flow,temperature and solute concentration fields,is applied to simulate experimental continuous casting cases with and without vertical electromagnetic...A volume averaged columnar solidification model,which couples the flow,temperature and solute concentration fields,is applied to simulate experimental continuous casting cases with and without vertical electromagnetic stirring(V-EMS).The calculated distribution of magnetic induction intensity and final macrosegregation maps are consistent with the experimental results.Calculation results reveal that the V-EMS promotes longitudinal melt flow,accelerates heat dissipation and solidification and finally reduces the central segregation of carbon.However,when V-EMS is applied,the solute distribution becomes asymmetric because the melt flow shows opposite directions between the near and far sides from stirrer.An obvious positive segregation band is observed at about 1/4 width of the billet near the stirrer in both calculated and experimental results.The position and degree of such positive segregation could be affected by installation height of stirrer,as demonstrated by additional simulation cases.展开更多
Liquid phase exfoliation(LPE)process for graphene production is usually carried out in stirred tank reactor and the interactions between the solvent and the graphite particles are important as to improve the productio...Liquid phase exfoliation(LPE)process for graphene production is usually carried out in stirred tank reactor and the interactions between the solvent and the graphite particles are important as to improve the production efficiency.In this paper,these interactions were revealed by computational fluid dynamics–discrete element method(CFD-DEM)method.Based on simulation results,both liquid phase flow hydrodynamics and particle motion behavior have been analyzed,which gave the general information of the multiphase flow behavior inside the stirred tank reactor as to graphene production.By calculating the threshold at the beginning of graphite exfoliation process,the shear force from the slip velocity was determined as the active force.These results can support the optimization of the graphene production process.展开更多
Conventionally, multiple reference frame(MRF) method and sliding mesh(SM) method are used in the simulation of stirred tanks, however, both methods have limitations. In this study, a hybrid immersed-boundary(IB)techni...Conventionally, multiple reference frame(MRF) method and sliding mesh(SM) method are used in the simulation of stirred tanks, however, both methods have limitations. In this study, a hybrid immersed-boundary(IB)technique is developed in a finite difference context for the numerical simulation of stirred tanks. IBs based on Lagrangian markers and solid volume fractions are used for moving and stationary boundaries, respectively, to achieve optimal efficiency and accuracy. To cope with the high computational cost in the simulation of stirred tanks, the technique is implemented on computers with hybrid architecture where central processing units(CPUs) and graphics processing units(GPUs) are used together. The accuracy and efficiency of the present technique are first demonstrated in a relatively simple case, and then the technique is applied to the simulation of turbulent flow in a Rushton stirred tank with large eddy simulation(LES). Finally the proposed methodology is coupled with discrete element method(DEM) to accomplish particle-resolved simulation of solid suspensions in small stirred tanks. It demonstrates that the proposed methodology is a promising tool in simulating turbulent flow in stirred tanks with complex geometries.展开更多
A computational method of constraint stabilization and correction is introduced. The method is based on the Baumgart＇s one-step method. Constraint conditions are addressed to stabilize and correct the solution. Two e...A computational method of constraint stabilization and correction is introduced. The method is based on the Baumgart＇s one-step method. Constraint conditions are addressed to stabilize and correct the solution. Two examples are given to illustrate the results of the method.展开更多
Metal clusters RCCo_3(CO)_9(R-H,C1,Br,CH_3,Ph) were prepared in 18.8-57.3% yields from the reaction of cobalt(Ⅱ)salt and RCX_a under mild PTC conditions(latm CO,25℃).The cobalt salt was reduced to Co(CO)_4 in the pr...Metal clusters RCCo_3(CO)_9(R-H,C1,Br,CH_3,Ph) were prepared in 18.8-57.3% yields from the reaction of cobalt(Ⅱ)salt and RCX_a under mild PTC conditions(latm CO,25℃).The cobalt salt was reduced to Co(CO)_4 in the presence of Na_3S_2O_4.展开更多
Liquid-liquid dispersion is often performed in stirred tanks,which are valued for their ease of operation,high droplet generation rate and effective droplet dispersion.Many relevant simulations use the Eulerian-Euleri...Liquid-liquid dispersion is often performed in stirred tanks,which are valued for their ease of operation,high droplet generation rate and effective droplet dispersion.Many relevant simulations use the Eulerian-Eulerian method,combining population balance equations with statistical models to forecast droplet breakage.Conversely,the Eulerian-Lagrangian(E-L)method provides precise tracking of individual droplets,which is crucial for simulating dispersion processes.However,E-L simulation faces challenges in integrating droplet breakage effectively.To address this issue,our research introduces a probabilistic approach for droplet breakages.It assumes that a longer time increases the likelihood of breakup;a droplet breaks if the calculated probability exceeds a random value from 0 to 1.Consequently,the simulated breakage frequency becomes independent of the Lagrangian time step.The Sauter mean diameter and droplet size distribution can be accurately predicted by this probabilistic approach.By closely monitoring droplet motion,we reveal the complexity of droplet trajectories and the detailed patterns of circulation in stirred tanks.These insights contribute to a deeper understanding of liquidliquid dispersion dynamics.展开更多
文摘BACKGROUND Inflammatory bowel disease(IBD)is a common chronic intestinal inflammatory disease.High oxidative stress is a treatment target for IBD.Cerium oxide(CeO2)nanomaterials as nanozymes with antioxidant activity are potential drugs for the treatment of colitis.AIM To synthesize hollow cerium(H-CeO2)nanoparticles by one-step method and to validate the therapeutic efficacy of H-CeO2 in IBD.METHODS H-CeO2 was synthesized by one-step method and examined its characterization and nanoenzymatic activity.Subsequently,we constructed dextran sulfate so-dium(DSS)-induced colitis in mice to observe the effects of H-CeO2 on colonic inflammation.The effects of H-CeO2 on colon inflammation and reactive oxygen species(ROS)levels in IBD mice were detected by hematoxylin and eosin staining and dichlorofluorescein diacetate staining,respectively.Finally,the biological sa-fety of H-CeO2 on mice was evaluated by hematoxylin and eosin staining,blood routine,and blood biochemistry.RESULTS H-CeO2 nanoparticles prepared by the one-step method were uniform,monodi-sperse and hollow.H-CeO2 had a good ability to scavenge ROS,∙OH and∙OOH.H-CeO2 reduced DSS-induced decreases in body weight and colon length,colonic epithelial damage,inflammatory infiltration,and ROS accumulation.H-CeO2 administration reduced the disease activity index of DSS-induced animals from about 8 to 5.H-CeO2 had no significant effect on body weight,total platelet count,hemoglobin,white blood cell,and red blood cell counts in healthy mice.No significant damage to major organs was observed in healthy mice following H-CeO2 administration.CONCLUSION The one-step synthesis of H-CeO2 nanomaterials had good antioxidant activity,biosafety,and inhibited deve-lopment of DSS-induced IBD in mice by scavenging ROS.
基金Item Sponsored by Grant-in-Aid for Young Scientists (B) (No.21760597) from the Japan Society for the Promotion of Science (JSPS)
文摘Rheocasting with semi-solid slurry has been widely used in industrial processes in recent years.The Cup-Cast method is one of the most effective ways to produce semi-solid slurry for rheocasting.In order to study the effect of electromagnetic stirring on the fabrication of semi-solid slurry,we have applied the Double-Axis-Electromagnetic Stirrer(DAEMS)to the Cup-Cast method.Microstructure of the slurry was observed by an optical microscope and Electron Back-Scatter Patterns(EBSP).The results indicated that the electromagnetic stirrer made it possible to accelerate the cooling rate of the melt,thus resulting in a higher quality slurry.
基金supported by the National Natural Science Foundation of China (No.52274304)。
文摘The three-dimensional(3D) Pd-based nanoflower structures,assembled from two-dimensional(2D)nanosheets,are characterized by their stable and ordered configurations.These structures have been extensively designed as anode materials for fuel cells.However,the exploration of trimetallic nanoflowers with porous architectures remains limited.In this study,we present a straightforward one-step solvothermal method for the synthesis of trimetallic Pd Cu Ni porous nanoflowers(PNFs).Leveraging several unique advantages,such as an open superstructure,high porosity,and enhanced electronic interactions among the trimetals,the resulting Pd Cu Ni PNFs demonstrate significantly improved electrochemical performance,with mass activities reaching 5.94 and 10.14 A/mg for the ethanol oxidation reaction(EOR)and the ethylene glycol oxidation reaction(EGOR),respectively.Furthermore,the Pd Cu Ni PNFs exhibit optimized d-band centers and the most negative onset oxidation potential,indicating enhanced antitoxicity and stability.This study not only provides a novel perspective on the synthesis of 3D porous nanomaterials but also highlights the potential application value of trimetallic nanoalloys in catalysis.
基金Project(ASM-20240)supported by the Key Laboratory of Advanced Structural Materials(Changchun University of Technology),Ministry of Education,ChinaProject(2022TD-30)supported by the Scientific and Technological Innovation Team Project of Shaanxi Innovation Capability Support Plan,China。
文摘This work examines the microstructure and corrosion properties of fine-grained Al 7075 across different regions under varying cooling conditions during friction stir welding.The findings demonstrate that forced cooling significantly improves the corrosion resistance of the welded joints.Specifically,the corrosion resistance was the highest in the stir zone,followed by the thermo-mechanical affected zone,and then the heat affected zone.Forced cooling mitigates grain growth by controlling the welding thermal effects,thereby increasing the proportion ofΣ3 grain boundaries.The modification of these microstructural characteristics promotes the formation of a dense oxide layer,thereby enhancing the corrosion resistance.Furthermore,forced cooling mitigates the precipitation and coarsening of the anodic phase in the stir zone,which in turn reduces the susceptibility of the joint to pitting corrosion.Additionally,the lower recrystallization texture content in the joint,resulting from forced cooling,contributes to a reduction in the number of corrosion-active sites,thereby further improving the corrosion performance of the welded joint.
文摘The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures were compared under mold electromagnetic stirring （MEMS） conditions （current of 300 A and frequency of 3 Hz）. Thereafter, the solidification structures of the large round billet were investigated under different superheats, casting speeds, and secondary cooling intensities. Finally, the effect of the MEMS current on the solidification structures was obtained under fixed superheat, casting speed, secondary cooling intensity, and MEMS frequency. The model accurately simulated the actual solidification structures of any steel, regardless of its size and the parameters used in the continuous casting process. The ratio of the central equiaxed grain zone was found to increase with decreasing superheat, increasing casting speed, decreasing secondary cooling intensity, and increasing MEMS current. The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.
基金Item Sponsored by Austrian competence centre programme COMET by the BMVITby the BMWFJ+1 种基金by the provinces of Upper Austria,Styria and Tyrolby the SFG and by the Tiroler Zukunftsstiftung
文摘In modern continuous casting of round steel blooms rotating electromagnetic fields are commonly employed to improve the product quality.Mould-electromagnetic stirrers(M-EMS)are used to excite a rotary motion along the solidification front in the liquid core.These velocities lead to a better strand surface quality as well as enhancing the transition from columnar to equiaxed solidification.Although the usage of electromagnetic stirrers is widespread,not all effects are fully known or understood.Due to harsh conditions at the plant,measurements are scarce and limited.Water model experiments-an established alternative for investigating continuous casting of steel-cannot be used due to the low electrical conductivity of water.Experiments with liquid metals like mercury,Galinstan or Wood’s metal are either expensive or difficult to perform.Thus numeric simulations are essential to gain a better understanding of the processes involved in continuous casting with electromagnetic stirring.However numeric simulations should always be validated with experiments and/or measurements.While the velocity field inside the liquid core of the bloom cannot be measured at the caster,the velocity at the mould level can be measured by dipping a nail into it.The skull forming at the tip of the nail is directly linked to the occurring surface velocity.These measurements can then be compared with numeric simulations of the nail dipping process.The numeric model is restricted to the upper part of the strand.The lower part of the strand is also taken into account through adjusted boundary conditions(velocity field etc.taken from a simulation of the whole strand).In this work the influence of the stirring field strength on the simulation results will be investigated.In the future these nail dipping simulations will be validated with plant measurements.This can then to a certain extentvalidate the simulation of the strand with M-EMS too,as it serves as the basis for the nail dipping model.
文摘Gradiently denitrated gun propellant(GDGP)prepared by a“gradient denitration”strategy is obviously superior in progressive burning performance to the traditional deterred gun propellant.Currently,the preparation of GDGP employed a tedious two-step method involving organic solvents,which hinders the large-scale preparation of GDGP.In this paper,GDGP was successfully prepared via a novelty and environmentally friendly one-step method.The obtained samples were characterized by FT-IR,Raman,SEM and XPS.The results showed that the content of nitrate groups gradiently increased from the surface to the core in the surface layer of GDGP and the surface layer of GDGP exhibited a higher compaction than that of raw gun propellant,with a well-preserved nitrocellulose structure.The denitration process enabled the propellant surface with regressive energy density and good progressive burning performance,as confirmed by oxygen bomb and closed bomb test.At the same time,the effects of different solvents on the component loss of propellant were compared.The result showed that water caused the least component loss.Finally,the stability of GDGP was confirmed by methyl-violet test.This work not only provided environmentally friendly,simple and economic preparation of GDGP,but also confirmed the stability of GDGP prepared by this method.
基金Item Sponsored by Natural Science Foundation of Liaoning Province[No.20092002]the Program of Introducing Talents of Discipline to Universities[No.B07015]
文摘Aimed at the problem of short life of mixing head in KR mechanical mixing method for desulfurization of hot metal,a new type of mixing stir was proposed.CFD theory was used to simulate the characteristics of the fluid flow for the new type of stirring vessel of water model for KR mechanical desulfurization.Flow characteristics and structures of the flow field were investigated and compared with the traditional cross-flow type.The results show that the new type of impeller can not only improve the defects of the flow caused by stir structure of the traditional type,but also reduce the separation of mixing zone in the stirred tank and make the flow field more uniform to make the desulfurization more fully, thus shortening the mixing time,and improving the life of mixing head.Numerical simulation method has been proven to be sound by comparing with the experimental ones.
文摘Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotational speed,welding speed,and tool tilt angle play a major role in deciding the joint characteristics.The joints fabricated using tapered square pin profile tool with a tool rotational speed of600r/min,welding speed of65mm/min,and tool tilt angle of1.5°result in an unexpected weld efficiency of93.51%.Mathematical models are developed to map the correlation between the parameters and responses(ultimate tensile strength and elongation)and these models are optimized to maximize the ultimate tensile strength of the friction stir welded joint.Response plots generated from the mathematical models are used to interpret the interaction effects of the welding parameters on the response variables.Adequacy of the developed models is validated using analysis of variance(ANOVA)technique.Results from the confirmatory experiments plotted in scatter diagram show a good agreement with predicted models.Different grain structures in various zones of the weld are examined by observing the micro and macro structures of the weld.
基金supported by the National Natural Science Foundation of China(No.50974035)National Natural Science Foundation of China(No.51074047)+2 种基金the doctoral fund of EDU gov(20090407)China Postdoctoral Science Foundation,(20090451277)Key scientific and technological program in Liaoning Province(200921007)
文摘This paper presents a new idea about desulfurization with in-situ mechanical stirring method on the basis of desulfurization by single blow grain magnesium and KR method, that is, the inner gases carry the magnesium vapor formed in-site in molten iron by magnesium-based desulfurization, and bubble dispersed and disintegrated under the condition of mechanical stirring, thence to improve the efficiency of desulfurization by single blow grain magnesium .It has been proved by research of cold water model experiment that the bubble dispersion and disintegration can not only improve the desulphurization efficiency but also increase the utilization rate of magnesium. Obviously, the bubble dispersion and disintegration of magnesium vapor is the key problem in improving the desulphurization efficiency and increasing the utilization rate of magnesium. Thus the research focus on exploring the performance of bubble dispersion and disintegration on the base of refining process and gas-liquid mass transfer. According to the literature and cold water model experimental result basing on principle of similitude, the influencing factors and interaction of bubble dispersion and disintegration have been studied from the perspectives of physical and numerical simulation. The study would provide the theoretical and experimental data for the new method of desulfurization with in-situ mechanical stirring.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10572021 and 10372053）, and the Fundamental Research Foundation of Beijing Institute of Technology （BIT-UBF-200507A4206）.
文摘In this paper, a new computational method for improving the accuracy of numerically computed solutions is introduced. The computational method is based on the one-step method and conserved quantities of holonomic systems are considered as kinematical constraints in this method.
基金financial support from the National Natural Science Foundation of China(Grant No.U1760206)the National Key R&D Program of China(Grant No.2017YFE0107900)+1 种基金the 111 Project 2.0 of China(Grant No.BP0719037)the financial support provided by the ESA-MAP MICAST project contract 14347/01/NL/SH.
文摘A volume averaged columnar solidification model,which couples the flow,temperature and solute concentration fields,is applied to simulate experimental continuous casting cases with and without vertical electromagnetic stirring(V-EMS).The calculated distribution of magnetic induction intensity and final macrosegregation maps are consistent with the experimental results.Calculation results reveal that the V-EMS promotes longitudinal melt flow,accelerates heat dissipation and solidification and finally reduces the central segregation of carbon.However,when V-EMS is applied,the solute distribution becomes asymmetric because the melt flow shows opposite directions between the near and far sides from stirrer.An obvious positive segregation band is observed at about 1/4 width of the billet near the stirrer in both calculated and experimental results.The position and degree of such positive segregation could be affected by installation height of stirrer,as demonstrated by additional simulation cases.
基金National Natural Science Foundation of China(U2004176,22008055)Technology Research Project of Henan Province(232102240034)are gratefully acknowledged.
文摘Liquid phase exfoliation(LPE)process for graphene production is usually carried out in stirred tank reactor and the interactions between the solvent and the graphite particles are important as to improve the production efficiency.In this paper,these interactions were revealed by computational fluid dynamics–discrete element method(CFD-DEM)method.Based on simulation results,both liquid phase flow hydrodynamics and particle motion behavior have been analyzed,which gave the general information of the multiphase flow behavior inside the stirred tank reactor as to graphene production.By calculating the threshold at the beginning of graphite exfoliation process,the shear force from the slip velocity was determined as the active force.These results can support the optimization of the graphene production process.
基金Supported by the National Natural Science Foundation of China(21225628,51106168,11272312)the“Strategic Priority Research Program”of the Chinese Academy of Sciences(XDA07080000)
文摘Conventionally, multiple reference frame(MRF) method and sliding mesh(SM) method are used in the simulation of stirred tanks, however, both methods have limitations. In this study, a hybrid immersed-boundary(IB)technique is developed in a finite difference context for the numerical simulation of stirred tanks. IBs based on Lagrangian markers and solid volume fractions are used for moving and stationary boundaries, respectively, to achieve optimal efficiency and accuracy. To cope with the high computational cost in the simulation of stirred tanks, the technique is implemented on computers with hybrid architecture where central processing units(CPUs) and graphics processing units(GPUs) are used together. The accuracy and efficiency of the present technique are first demonstrated in a relatively simple case, and then the technique is applied to the simulation of turbulent flow in a Rushton stirred tank with large eddy simulation(LES). Finally the proposed methodology is coupled with discrete element method(DEM) to accomplish particle-resolved simulation of solid suspensions in small stirred tanks. It demonstrates that the proposed methodology is a promising tool in simulating turbulent flow in stirred tanks with complex geometries.
基金the National Natural Science Foundation of China (10572021 ,10372053)Basic Research Foundation of Beijing Institute of Tech-nology (BIT-UBF-200507A4206)
文摘A computational method of constraint stabilization and correction is introduced. The method is based on the Baumgart＇s one-step method. Constraint conditions are addressed to stabilize and correct the solution. Two examples are given to illustrate the results of the method.
文摘Metal clusters RCCo_3(CO)_9(R-H,C1,Br,CH_3,Ph) were prepared in 18.8-57.3% yields from the reaction of cobalt(Ⅱ)salt and RCX_a under mild PTC conditions(latm CO,25℃).The cobalt salt was reduced to Co(CO)_4 in the presence of Na_3S_2O_4.
基金support from the National Key Research and Development Program of China,China(2023YFE0106600)the National Natural Science Foundation of China,China(22421003,22178354,21925805)funding from FFG(Austria)under project“ABATE”(903872).
文摘Liquid-liquid dispersion is often performed in stirred tanks,which are valued for their ease of operation,high droplet generation rate and effective droplet dispersion.Many relevant simulations use the Eulerian-Eulerian method,combining population balance equations with statistical models to forecast droplet breakage.Conversely,the Eulerian-Lagrangian(E-L)method provides precise tracking of individual droplets,which is crucial for simulating dispersion processes.However,E-L simulation faces challenges in integrating droplet breakage effectively.To address this issue,our research introduces a probabilistic approach for droplet breakages.It assumes that a longer time increases the likelihood of breakup;a droplet breaks if the calculated probability exceeds a random value from 0 to 1.Consequently,the simulated breakage frequency becomes independent of the Lagrangian time step.The Sauter mean diameter and droplet size distribution can be accurately predicted by this probabilistic approach.By closely monitoring droplet motion,we reveal the complexity of droplet trajectories and the detailed patterns of circulation in stirred tanks.These insights contribute to a deeper understanding of liquidliquid dispersion dynamics.
