Processes of filtering two-phase media in filtration devices play an important role in various industries. Significant role in the process of filtering is the initial section of flow, which defines the basic parameter...Processes of filtering two-phase media in filtration devices play an important role in various industries. Significant role in the process of filtering is the initial section of flow, which defines the basic parameters： the profile and value of the velocity, pressure gradients, concentration and dispersion of sediment particles, etc.. The problem is solved by the method of surfaces of equal cost, the results enabled to establish the influence of the input section on the filtering process.展开更多
The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are b...The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are based on Eulerian framework,which is not enough for developing the probability density function(PDF) model.In this paper,the instantous behavior and multi-particle statistics of passive scalar along inertial particle trajectory,in homogenous isotropic turbulence with a mean scalar gradient,are investigated by using the direct numerical simulation(DNS).The results show that St^1.0 particles are easy to aggregate in high strain and low vorticity regions in the fluid field,where the scalar dissipation is usually much higher than the mean value,and that every time they move across the cliff structures,the scalar change is much more intensive.Anyway,the self-correlation of scalar along particle trajectory is significantly different from the velocities observed by particle,for which the prefer-concentration effect is evident.The mechanical-to-thermal time scale ratio averaged along the particles,<r> p,is approximately two times smaller than that computed in the Eulerian frame r,and stays at nearly 1.77 with a weak dependence on particle inertia.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
Fluid flow and mixing of molten steel in a twin-slab-strand continuous casting tundish were investigated using a mixing model under non-isothermal conditions.This model led to a set of ordinary differential equations ...Fluid flow and mixing of molten steel in a twin-slab-strand continuous casting tundish were investigated using a mixing model under non-isothermal conditions.This model led to a set of ordinary differential equations that were solved with a Runge-Kutta algorithm.Steady state water modeling was carried out under non-isothermal conditions.Experimental data obtained from the water model were used to calibrate the mixing model.Owing to the presence of a mixed convection in the non-isothermal conditions,a channelizing flow would be created in the fluid inside the tundish.A mixing model was designed that was capable of predicting RTD（residence time distribution）curves for different cases in non-isothermal conditions.The relationship between RTD parameters and the Tu（tundish Richardson number）was obtained for various cases under non-isothermal conditions.The results show that the RTD parameters were completely different under isothermal and non-isothermal conditions.The comparison of the RTD curves between the isothermal and non-isothermal conditions presents that the extent of mixing in the tundish in non-isothermal conditions is lower than the mixing extent in isothermal conditions.展开更多
Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a cry...Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.展开更多
This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries.Such an organization is used to g...This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries.Such an organization is used to generate the heat exchangers with tube and shell because of the production of more turbulence due to zigzag path which is in favor of rapid heat transformation.Because of little maintenance,the heat exchanger of such type is extensively used.Here,we generate simulation of flow and heat transfer using nonisothermal flow interface in the Comsol multiphysics 5.4 which executes the Reynolds averaged Navier stokes equation(RANS)model of the turbulent flow together with heat equation.Simulation is tested with Prandtl number(Pr=0.7)with inlet velocity magnitude in the range from 1 to 2 m/sec which generates the Reynolds number in the range of 2.2×10^(5) to 4.4×10^(5) with turbulence kinetic energy and the dissipation rate in ranges(3.75×10^(−3) to 1.5×10^(−2))and(3.73×10^(−3)−3×10^(−2))respectively.Two correlations available in the literature are used in order to check validity.The results are displayed through streamlines,surface plots,contour plots,isothermal lines,and graphs.It is concluded that by retaining such an arrangement a quick distribution of the temperature over the domain can be seen and also the velocity magnitude is increasing from 333.15%to a maximum of 514%.The temperature at the middle shows the consistency in value but declines immediately at the end.This process becomes faster with the decrease in inlet velocity magnitude.展开更多
Non-isothermal aging(NIA)is a composite heat treatment process that involves heating aging,cooling aging,and complex solute precipitation sequences.The precipitation behavior and the strengthening and toughening mecha...Non-isothermal aging(NIA)is a composite heat treatment process that involves heating aging,cooling aging,and complex solute precipitation sequences.The precipitation behavior and the strengthening and toughening mechanisms of the 2014 Al alloy during NIA were studied by employing tensile,fatigue crack growth,hardness,and electronic conductivity tests,as well as high-resolution transmission electron microscopy and scanning electron microscopy.The results show that during NIA,theθ′phase exhibits a complex process of nucleation,nucleation and growth,nucleation and growth and coarsening,growth and coarsening,nucleation and growth,and nucleation.NIA treatment imparts a mixed precipitation characteristic on the alloy,which is manifested as coherent precipitates,including GP zones,θ′′phases,small-sizedθ′phases,and semi-coherent or non-coherent precipitates such as large-sizedθ′phases and equilibriumθphases.The simultaneous strengthening and toughening of the NIA-treated 2014 Al alloy is caused by the synergistic effects of the particle-shearing mechanism and Orowan bypassing mechanism.展开更多
Non-isothermal aging(NIA)treatments have presented significant advantages in improving the comprehensive performance and aging hardening efficiency of the 7000 series aluminum alloys,but there is no attention paid to ...Non-isothermal aging(NIA)treatments have presented significant advantages in improving the comprehensive performance and aging hardening efficiency of the 7000 series aluminum alloys,but there is no attention paid to their composites.This study takes a linear heating aging process as an example to reveal the precipitation behaviors of a 15 vol.%SiC/7085Al composite as well as its impact on mechanical properties using differential scanning calorimetry,transmission electron microscopy,small-angle neutron scattering,hardness measurements,and tensile testing.The results indicated the formation of GP(Ⅰ,Ⅱ)zones,η’andηprecipitates in sequence,leading to the hardness and strength initially increasing and then decreasing with rising NIA temperatures.The maximums were reached at 183℃,corresponding to the appearance ofη’precipitates in large quantities.Owing to the rapid temperature rise during the NIA process,the precipitates entered the coarsening and redissolution stage before they were entirely formed,resulting in reduced peak strength compared to the T6 treatment.The composite exhibited a more significant reduction in strength than the 7085Al alloy because:(i)the annihilation of vacancies suppressed the formation of GPII zones,thereby weakening their transition toη’precipitates;(ii)quenching dislocations promoted the coarsening of precipitates.An improved NIA process,incorporating both heating and cooling aging treatments,was effectively designed with the assistance of in-situ SANS technology to address this issue,which allows for achieving strength comparable to that after the T6 treatment with only 15%of the aging time consumption.This research fills the gap in investigating the NIA precipitation behaviors of aluminum matrix composites,providing guidance for the formulation of NIA schedules.展开更多
To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior,isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator a...To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior,isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator at temperatures of 380-440℃and strain rates of 0.05-1 s^(−1).The Johnson-Cook model,Hensel-Spittel model,strain-compensated Arrhenius model,and critical fracture strain model were established.Results show that through the evaluation of the models using the correlation coefficient(R)and the average absolute relative error,the strain-compensated Arrhenius model can represent the flow behavior of the alloy more accurately.Shear bands are more pronounced in the as-homogenized specimens,whereas dynamic recrystallization is predominantly observed in as-rolled specimens.Fracture morphology analysis reveals that a mixed fracture mechanism is prevalent in the as-homogenized specimen,whereas a ductile fracture mechanism is predominant in the as-rolled specimen.The processing maps indicate that the unstable region is reduced in the as-rolled specimens compared with that in the as-homogenized specimens.The optimal hot working windows for the as-homogenized and as-rolled specimens are determined as 410-440℃/0.14-1 s^(−1)and 380-400℃/0.05-0.29 s^(−1),respectively.展开更多
The paper explores the gravity-driven flow of the thin film of a viscoelastic-fluid-based nanofluids(VFBN)along an inclined plane under non-isothermal conditions and subjected to convective cooling at the free-surface...The paper explores the gravity-driven flow of the thin film of a viscoelastic-fluid-based nanofluids(VFBN)along an inclined plane under non-isothermal conditions and subjected to convective cooling at the free-surface.The Newton’s law of cooling is used to model the convective heat-exchange with the ambient at the free-surface.The Giesekus viscoelastic constitutive model,with appropriate modifications to account for non-isothermal effects,is employed to describe the polymeric effects.The unsteady and coupled non-linear partial differential equations(PDEs)describing the model problem are obtained and solved via efficient semi-implicit numerical schemes based on finite difference methods(FDM)implemented in Matlab.The response of the VFBN velocity,temperature,thermal-conductivity and polymeric-stresses to variations in the volume-fraction of embedded nanoparticles is investigated.It is shown that these quantities all increase as the nanoparticle volume-fraction becomes higher.展开更多
Vanadium redox flow batteries(VRFBs)are a means of large-scale energy storage due to their excellent scalability,safety,long cycling life,and decoupled power and energy capacities.However,the slow redox kinetics of va...Vanadium redox flow batteries(VRFBs)are a means of large-scale energy storage due to their excellent scalability,safety,long cycling life,and decoupled power and energy capacities.However,the slow redox kinetics of vanadium species on conventional carbon electrodes remains a major limitation to their performance.We investigated the deposition of carbon black,carbon nanotubes,and electrochemically exfoliated graphene(Exf-Gr)onto thermally-activated carbon paper(ACP)by spray coating to increase the electrode electrocatalytic activity.The modified electrodes were characterized using scanning electron microscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron microscopy,and surface area analysis,while their electrochemical properties were evaluated by cyclic voltammetry,electrochemical impedance spectroscopy,and singlecell VRFB testing.Among the modified electrodes,Exf-Gr/ACP had the best performance,achieving a 2.9-fold reduction in charge transfer resistance compared to pristine ACP and delivering 2.5 times the discharge capacity in single-cell tests.This improvement is attributed to Exf-Gr’s high surface area,favorable catalytic activity,and excellent dispersion on the ACP substrate.Surface modification with electrochemically exfoliated graphene is a highly effective strategy for improving the electrode performance in VRFB systems,with significant implications for large-scale energy storage.展开更多
Large-eddy simulation(LES)is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate.The simulation is performed using a fi...Large-eddy simulation(LES)is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate.The simulation is performed using a finite difference method,with the air-water interface captured by a coupled level-set and volume-of-fluid method.Four cases are conducted to investigate the effects of Froude number on turbulent statistics,including the mean velocity,turbulence kinetic energy,and turbulence mass flux(TMF),which is an additional unclosed term in the Reynolds-averaged momentum equation.The TMF,especially its vertical component,shows a complex behaviour with respect to the Froude number.This property of the TMF imposes high demands on the robustness of the closure model of TMF.The present LES data is further used to examine a closure model of the TMF production term,which shows a high correlation with the data obtained from LES.展开更多
To clarify fluid flow mechanisms and establish effective development conditions in continental shale oil reservoirs,a high-temperature,high-pressure steady-state flow system integrated with nuclear magnetic resonance(...To clarify fluid flow mechanisms and establish effective development conditions in continental shale oil reservoirs,a high-temperature,high-pressure steady-state flow system integrated with nuclear magnetic resonance(NMR)technology has been developed.The apparatus combines sample evacuation,rapid pressurization and saturation,and controlled displacement,enabling systematic investigation of single-phase shale oil flow under representative reservoir conditions.Related experiments allow proper quantification of the activation thresholds and relative contributions of different pore types to flow.A movable fluid index(MFI),defined using dual T_(2) cutoff values,is introduced accordingly and linked to key flow parameters.The results reveal distinct multi-scale characteristics of single-phase shale oil transport,namely micro-scale graded displacement and macro-scale segmented nonlinear behavior.As the injection-production pressure difference increases,flow pathways are activated progressively,beginning with fractures,followed by large and then smaller macropores,leading to a pronounced enhancement in apparent permeability.Although mesopores and micropores contribute little to direct flow,their indirect influence becomes increasingly important,and apparent permeability gradually approaches a stable limit at higher pressure difference.It is also shown that the MFI exhibits a strong negative correlation with the starting pressure gradient and a positive correlation with apparent permeability,providing a rapid and reliable indicator of shale oil flow capacity.Samples containing through-going fractures display consistently higher MFI values and superior flowability compared with those dominated by laminated fractures,highlighting the pivotal role of well-connected fracture networks generated by large-scale hydraulic fracturing in improving shale oil production.展开更多
Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section...Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section of the Wuhai-Maqin Expressway as a case study,employing CFD numerical simulation methods to calculate and analyze the wind-sand flow field distribution characteristics in different longitudinal slope sections.The results show that:(1)Along with the direction of the incoming flow,the windward and leeward slope toes of the embankment are low-wind-speed zones,with the wind speed at the leeward slope toe being even lower.The higher the embankment,the larger the low-wind-speed zone at the windward and leeward slope toes.As the longitudinal slope increases,the extent of the lowwind-speed zone at the same location along the route also increases.(2)Along the route direction,the wind speed at the windward and leeward slope toes decreases as embankment height increases.At the embankment toe,sand particles are transported from the top to the bottom of the longitudinal slope,and the greater the longitudinal slope,the stronger the transport effect.(3)Along the route direction,the sand accumulation around the embankment gradually gathers toward the bottom of the longitudinal slope as the slope increases.When the longitudinal slope is 3%and 4%,the trend of sand accumulation moving from the windward side at the end of the route to the leeward side at the start of the route is more significant.When the longitudinal slope is less than or equal to 3%,severe sand accumulation within the embankment range is reduced by 86.4%or more compared to when the slope is 4%.(4)Under the same longitudinal slope,the higher the embankment height,the smaller its transport rate.When the embankment height is the same,the greater the longitudinal slope,the greater the embankment transport rate.展开更多
The newly formulated non-Newtonian rivulet flows streaming down an inclined planar surface,with additional periodic perturbations arising from the application of the 2nd Stokes problem to the investigation of rivulet ...The newly formulated non-Newtonian rivulet flows streaming down an inclined planar surface,with additional periodic perturbations arising from the application of the 2nd Stokes problem to the investigation of rivulet dynamics,are demonstrated in the current research.Hereby,the 2nd Stokes problem assumes that the surface,with a thin shared layer of the fluid on it,oscillates in a harmonic manner along the x-axis of the rivulet flow,which coincides with the main flow direction streaming down the underlying surface.We obtain the exact extension of the rivulet flow family,clarifying the structure of the pressure field,which fully absorbs the arising perturbation.The profile of the velocity field is assumed to be Gaussian-type with a non-zero level of plasticity.Hence,the absolutely non-Newtonian case of the viscoplastic flow solution,which satisfies the motion and continuity equations,is considered(with particular cases of exact solutions for pressure).The perturbed governing equations of motion for rivulet flows then result in the Riccati-type ordinary differential equation(ODE),describing the dynamics of the coordinate x(t).The approximated schematic dynamics are presented in graphical plots.展开更多
Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forc...Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forcing.They also underpin practical applications ranging from environmental transport to high-speed and aerothermal systems.Despite decades of progress,prediction remains difficult.The physics spans a wide range of scales and often couples turbulence,interphase momentum exchange,collisions,and interfacial transport.Reliable computation therefore requires both robust numerical methodology and careful physical interpretation.展开更多
The present study aims at investigating the effect of temperature variation due to heat transfer between the formation and drilling fluids considering influx from the reservoir in the underbalanced drilling condition....The present study aims at investigating the effect of temperature variation due to heat transfer between the formation and drilling fluids considering influx from the reservoir in the underbalanced drilling condition. Gas-liquid-solid three-phase flow model considering transient thermal interaction with the formation was applied to simulate wellbore fluid to calculate the wellbore temperature and pressure and analyze the influence of different parameters on fluid pressure and temperature distribution in annulus. The results show that the non-isothermal three-phase flow model with thermal consideration gives more accurate prediction of bottom-hole pressure(BHP) compared to other models considering geothermal temperature. Viscous dissipation, the heat produced by friction between the rotating drilling-string and well wall and drill bit drilling, and influx of oil and gas from reservoir have significant impact on the distribution of fluid temperature in the wellbore, which in turn affects the BHP. Bottom-hole fluid temperature decreases with increasing liquid flow rate, circulation time, and specific heat of liquid and gas but it increases with increasing in gas flow rate. It was found that BHP is strongly depended on the gas and liquid flow rates but it has weak dependence on the circulation time and specific heat of liquid and gas. BHP increase with increasing liquid flow rate and decreases with increasing gas flow rate.展开更多
The Cooling-Storage-Ring External-target Experiment(CEE)at the Heavy Ion Research Facility in Lanzhou(HIRFL)is designed to study the properties of nuclear matter created in heavy-ion collisions at beam energies from a...The Cooling-Storage-Ring External-target Experiment(CEE)at the Heavy Ion Research Facility in Lanzhou(HIRFL)is designed to study the properties of nuclear matter created in heavy-ion collisions at beam energies from a few hundred MeV/u up to 1 GeV/u.It aims to facilitate research on the quantum chromodynamics(QCD)phase structure in the high-baryondensity region.Collective flow is a fundamental observable in heavy-ion collision experiments,providing information on the bulk properties of the produced matter.Although the standard event plane method has been widely used to measure collective flow,it is still important to validate and optimize this method for the CEE spectrometer.In this paper,we study the experimental procedures for measuring directed flow in^(238)U+^(238)U collisions at 500 MeV/u,using event planes reconstructed by Multi-Wire Drift Chamber and Zero Degree Calorimeter,respectively.Jet AA Microscopic(JAM)transport generator is used to generate events,and the detector response is simulated by the CEE Fast Simulation(CFS)package.Finally,the optimal kinematic region for proton directed flow measurements is discussed for the future CEE experiment.展开更多
The Reynolds-averaged Navier-Stokes(RANS)technique enables critical engineering predictions and is widely adopted.However,since this iterative computation relies on the fixed-point iteration,it may converge to unexpec...The Reynolds-averaged Navier-Stokes(RANS)technique enables critical engineering predictions and is widely adopted.However,since this iterative computation relies on the fixed-point iteration,it may converge to unexpected non-physical phase points in practice.We conduct an analysis on the phase-space characteristics and the fixed-point theory underlying the k-ε turbulence model,and employ the classical Kolmogorov flow as a framework,leveraging its direct numerical simulation(DNS)data to construct a one-dimensional(1D)system under periodic/fixed boundary conditions.The RANS results demonstrate that under periodic boundary conditions,the k-ε model exhibits only a unique trivial fixed point,with asymptotes capturing the phase portraits.The stability of this trivial fixed point is determined by a mathematically derived stability phase diagram,indicating the fact that the k-ε model will never converge to correct values under periodic conditions.In contrast,under fixed boundary conditions,the model can yield a stable non-trivial fixed point.The evolutionary mechanisms and their relationship with boundary condition settings systematically explain the inherent limitations of the k-ε model,i.e.,its deficiency in computing the flow field under periodic boundary conditions and sensitivity to boundary-value specifications under fixed boundary conditions.These conclusions are finally validated with the open-source code OpenFOAM.展开更多
文摘Processes of filtering two-phase media in filtration devices play an important role in various industries. Significant role in the process of filtering is the initial section of flow, which defines the basic parameters： the profile and value of the velocity, pressure gradients, concentration and dispersion of sediment particles, etc.. The problem is solved by the method of surfaces of equal cost, the results enabled to establish the influence of the input section on the filtering process.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50936001,51021065,50976042)the State Key Fundamental Research Program,Ministry of Science and Technology,China (Grant Nos. 2010CB227004,2011CB707301)
文摘The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are based on Eulerian framework,which is not enough for developing the probability density function(PDF) model.In this paper,the instantous behavior and multi-particle statistics of passive scalar along inertial particle trajectory,in homogenous isotropic turbulence with a mean scalar gradient,are investigated by using the direct numerical simulation(DNS).The results show that St^1.0 particles are easy to aggregate in high strain and low vorticity regions in the fluid field,where the scalar dissipation is usually much higher than the mean value,and that every time they move across the cliff structures,the scalar change is much more intensive.Anyway,the self-correlation of scalar along particle trajectory is significantly different from the velocities observed by particle,for which the prefer-concentration effect is evident.The mechanical-to-thermal time scale ratio averaged along the particles,<r> p,is approximately two times smaller than that computed in the Eulerian frame r,and stays at nearly 1.77 with a weak dependence on particle inertia.
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.
文摘Fluid flow and mixing of molten steel in a twin-slab-strand continuous casting tundish were investigated using a mixing model under non-isothermal conditions.This model led to a set of ordinary differential equations that were solved with a Runge-Kutta algorithm.Steady state water modeling was carried out under non-isothermal conditions.Experimental data obtained from the water model were used to calibrate the mixing model.Owing to the presence of a mixed convection in the non-isothermal conditions,a channelizing flow would be created in the fluid inside the tundish.A mixing model was designed that was capable of predicting RTD（residence time distribution）curves for different cases in non-isothermal conditions.The relationship between RTD parameters and the Tu（tundish Richardson number）was obtained for various cases under non-isothermal conditions.The results show that the RTD parameters were completely different under isothermal and non-isothermal conditions.The comparison of the RTD curves between the isothermal and non-isothermal conditions presents that the extent of mixing in the tundish in non-isothermal conditions is lower than the mixing extent in isothermal conditions.
基金Project(11102164)supported by the National Natural Science Foundation of ChinaProject(G9KY101502)supported by NPU Foundation for Fundamental Research,China
文摘Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.
文摘This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries.Such an organization is used to generate the heat exchangers with tube and shell because of the production of more turbulence due to zigzag path which is in favor of rapid heat transformation.Because of little maintenance,the heat exchanger of such type is extensively used.Here,we generate simulation of flow and heat transfer using nonisothermal flow interface in the Comsol multiphysics 5.4 which executes the Reynolds averaged Navier stokes equation(RANS)model of the turbulent flow together with heat equation.Simulation is tested with Prandtl number(Pr=0.7)with inlet velocity magnitude in the range from 1 to 2 m/sec which generates the Reynolds number in the range of 2.2×10^(5) to 4.4×10^(5) with turbulence kinetic energy and the dissipation rate in ranges(3.75×10^(−3) to 1.5×10^(−2))and(3.73×10^(−3)−3×10^(−2))respectively.Two correlations available in the literature are used in order to check validity.The results are displayed through streamlines,surface plots,contour plots,isothermal lines,and graphs.It is concluded that by retaining such an arrangement a quick distribution of the temperature over the domain can be seen and also the velocity magnitude is increasing from 333.15%to a maximum of 514%.The temperature at the middle shows the consistency in value but declines immediately at the end.This process becomes faster with the decrease in inlet velocity magnitude.
基金supported by the Science Foundation of Hunan Province,China(No.2020JJ5215)Scientific Research Project of Hunan Provincial Department of Education,China(No.21B0594)the Open Fund of Hunan Key Laboratory of Electromagnetic Equipment Design and Manufacturing,China(No.DC202007)。
文摘Non-isothermal aging(NIA)is a composite heat treatment process that involves heating aging,cooling aging,and complex solute precipitation sequences.The precipitation behavior and the strengthening and toughening mechanisms of the 2014 Al alloy during NIA were studied by employing tensile,fatigue crack growth,hardness,and electronic conductivity tests,as well as high-resolution transmission electron microscopy and scanning electron microscopy.The results show that during NIA,theθ′phase exhibits a complex process of nucleation,nucleation and growth,nucleation and growth and coarsening,growth and coarsening,nucleation and growth,and nucleation.NIA treatment imparts a mixed precipitation characteristic on the alloy,which is manifested as coherent precipitates,including GP zones,θ′′phases,small-sizedθ′phases,and semi-coherent or non-coherent precipitates such as large-sizedθ′phases and equilibriumθphases.The simultaneous strengthening and toughening of the NIA-treated 2014 Al alloy is caused by the synergistic effects of the particle-shearing mechanism and Orowan bypassing mechanism.
基金support of the Na-tional Key R&D Program of China(No.2021YFA1600700)the Na-tional Natural Science Foundation of China(grant Nos.U22A20114,52322106,52192595,and 52301200)+2 种基金the Project funded by China Postdoctoral Science Foundation(No.2023M733573)CSNS Con-sortium on High-performance Materials of Chinese Academy of Sciences(No.JZHKYPT-2021-01)the Natural Science Foun-dation of Liaoning Province(No.2023-BS-020)。
文摘Non-isothermal aging(NIA)treatments have presented significant advantages in improving the comprehensive performance and aging hardening efficiency of the 7000 series aluminum alloys,but there is no attention paid to their composites.This study takes a linear heating aging process as an example to reveal the precipitation behaviors of a 15 vol.%SiC/7085Al composite as well as its impact on mechanical properties using differential scanning calorimetry,transmission electron microscopy,small-angle neutron scattering,hardness measurements,and tensile testing.The results indicated the formation of GP(Ⅰ,Ⅱ)zones,η’andηprecipitates in sequence,leading to the hardness and strength initially increasing and then decreasing with rising NIA temperatures.The maximums were reached at 183℃,corresponding to the appearance ofη’precipitates in large quantities.Owing to the rapid temperature rise during the NIA process,the precipitates entered the coarsening and redissolution stage before they were entirely formed,resulting in reduced peak strength compared to the T6 treatment.The composite exhibited a more significant reduction in strength than the 7085Al alloy because:(i)the annihilation of vacancies suppressed the formation of GPII zones,thereby weakening their transition toη’precipitates;(ii)quenching dislocations promoted the coarsening of precipitates.An improved NIA process,incorporating both heating and cooling aging treatments,was effectively designed with the assistance of in-situ SANS technology to address this issue,which allows for achieving strength comparable to that after the T6 treatment with only 15%of the aging time consumption.This research fills the gap in investigating the NIA precipitation behaviors of aluminum matrix composites,providing guidance for the formulation of NIA schedules.
文摘To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior,isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator at temperatures of 380-440℃and strain rates of 0.05-1 s^(−1).The Johnson-Cook model,Hensel-Spittel model,strain-compensated Arrhenius model,and critical fracture strain model were established.Results show that through the evaluation of the models using the correlation coefficient(R)and the average absolute relative error,the strain-compensated Arrhenius model can represent the flow behavior of the alloy more accurately.Shear bands are more pronounced in the as-homogenized specimens,whereas dynamic recrystallization is predominantly observed in as-rolled specimens.Fracture morphology analysis reveals that a mixed fracture mechanism is prevalent in the as-homogenized specimen,whereas a ductile fracture mechanism is predominant in the as-rolled specimen.The processing maps indicate that the unstable region is reduced in the as-rolled specimens compared with that in the as-homogenized specimens.The optimal hot working windows for the as-homogenized and as-rolled specimens are determined as 410-440℃/0.14-1 s^(−1)and 380-400℃/0.05-0.29 s^(−1),respectively.
文摘The paper explores the gravity-driven flow of the thin film of a viscoelastic-fluid-based nanofluids(VFBN)along an inclined plane under non-isothermal conditions and subjected to convective cooling at the free-surface.The Newton’s law of cooling is used to model the convective heat-exchange with the ambient at the free-surface.The Giesekus viscoelastic constitutive model,with appropriate modifications to account for non-isothermal effects,is employed to describe the polymeric effects.The unsteady and coupled non-linear partial differential equations(PDEs)describing the model problem are obtained and solved via efficient semi-implicit numerical schemes based on finite difference methods(FDM)implemented in Matlab.The response of the VFBN velocity,temperature,thermal-conductivity and polymeric-stresses to variations in the volume-fraction of embedded nanoparticles is investigated.It is shown that these quantities all increase as the nanoparticle volume-fraction becomes higher.
基金supported by the University of Seoul’s 2025 Research Fund.
文摘Vanadium redox flow batteries(VRFBs)are a means of large-scale energy storage due to their excellent scalability,safety,long cycling life,and decoupled power and energy capacities.However,the slow redox kinetics of vanadium species on conventional carbon electrodes remains a major limitation to their performance.We investigated the deposition of carbon black,carbon nanotubes,and electrochemically exfoliated graphene(Exf-Gr)onto thermally-activated carbon paper(ACP)by spray coating to increase the electrode electrocatalytic activity.The modified electrodes were characterized using scanning electron microscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron microscopy,and surface area analysis,while their electrochemical properties were evaluated by cyclic voltammetry,electrochemical impedance spectroscopy,and singlecell VRFB testing.Among the modified electrodes,Exf-Gr/ACP had the best performance,achieving a 2.9-fold reduction in charge transfer resistance compared to pristine ACP and delivering 2.5 times the discharge capacity in single-cell tests.This improvement is attributed to Exf-Gr’s high surface area,favorable catalytic activity,and excellent dispersion on the ACP substrate.Surface modification with electrochemically exfoliated graphene is a highly effective strategy for improving the electrode performance in VRFB systems,with significant implications for large-scale energy storage.
基金supported by the National Natural Science Foundation of China(NSFC)Basic Science Center Program for‘Multiscale Problems in Nonlinear Mechanics’(Grant No.11988102)NSFC project(Grant No.11972038)Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087).
文摘Large-eddy simulation(LES)is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate.The simulation is performed using a finite difference method,with the air-water interface captured by a coupled level-set and volume-of-fluid method.Four cases are conducted to investigate the effects of Froude number on turbulent statistics,including the mean velocity,turbulence kinetic energy,and turbulence mass flux(TMF),which is an additional unclosed term in the Reynolds-averaged momentum equation.The TMF,especially its vertical component,shows a complex behaviour with respect to the Froude number.This property of the TMF imposes high demands on the robustness of the closure model of TMF.The present LES data is further used to examine a closure model of the TMF production term,which shows a high correlation with the data obtained from LES.
基金supported by the National Science and Technology Major Project of China(Grant No.2024ZD 1004302)the Key Scientific and Technological Research project of SINOPEC(Grant No.P25186).
文摘To clarify fluid flow mechanisms and establish effective development conditions in continental shale oil reservoirs,a high-temperature,high-pressure steady-state flow system integrated with nuclear magnetic resonance(NMR)technology has been developed.The apparatus combines sample evacuation,rapid pressurization and saturation,and controlled displacement,enabling systematic investigation of single-phase shale oil flow under representative reservoir conditions.Related experiments allow proper quantification of the activation thresholds and relative contributions of different pore types to flow.A movable fluid index(MFI),defined using dual T_(2) cutoff values,is introduced accordingly and linked to key flow parameters.The results reveal distinct multi-scale characteristics of single-phase shale oil transport,namely micro-scale graded displacement and macro-scale segmented nonlinear behavior.As the injection-production pressure difference increases,flow pathways are activated progressively,beginning with fractures,followed by large and then smaller macropores,leading to a pronounced enhancement in apparent permeability.Although mesopores and micropores contribute little to direct flow,their indirect influence becomes increasingly important,and apparent permeability gradually approaches a stable limit at higher pressure difference.It is also shown that the MFI exhibits a strong negative correlation with the starting pressure gradient and a positive correlation with apparent permeability,providing a rapid and reliable indicator of shale oil flow capacity.Samples containing through-going fractures display consistently higher MFI values and superior flowability compared with those dominated by laminated fractures,highlighting the pivotal role of well-connected fracture networks generated by large-scale hydraulic fracturing in improving shale oil production.
基金financially supported by Youth Science“Research on Failure Mechanism and Evaluation Method of Sand Control Measures for Railway Machinery in Sandy Area”(12302511)Ningxia Transportation Department Science and Technology Project(20200173)The Central Guidance on Local Science and Technology Development Funds(22ZY1QA005)。
文摘Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section of the Wuhai-Maqin Expressway as a case study,employing CFD numerical simulation methods to calculate and analyze the wind-sand flow field distribution characteristics in different longitudinal slope sections.The results show that:(1)Along with the direction of the incoming flow,the windward and leeward slope toes of the embankment are low-wind-speed zones,with the wind speed at the leeward slope toe being even lower.The higher the embankment,the larger the low-wind-speed zone at the windward and leeward slope toes.As the longitudinal slope increases,the extent of the lowwind-speed zone at the same location along the route also increases.(2)Along the route direction,the wind speed at the windward and leeward slope toes decreases as embankment height increases.At the embankment toe,sand particles are transported from the top to the bottom of the longitudinal slope,and the greater the longitudinal slope,the stronger the transport effect.(3)Along the route direction,the sand accumulation around the embankment gradually gathers toward the bottom of the longitudinal slope as the slope increases.When the longitudinal slope is 3%and 4%,the trend of sand accumulation moving from the windward side at the end of the route to the leeward side at the start of the route is more significant.When the longitudinal slope is less than or equal to 3%,severe sand accumulation within the embankment range is reduced by 86.4%or more compared to when the slope is 4%.(4)Under the same longitudinal slope,the higher the embankment height,the smaller its transport rate.When the embankment height is the same,the greater the longitudinal slope,the greater the embankment transport rate.
文摘The newly formulated non-Newtonian rivulet flows streaming down an inclined planar surface,with additional periodic perturbations arising from the application of the 2nd Stokes problem to the investigation of rivulet dynamics,are demonstrated in the current research.Hereby,the 2nd Stokes problem assumes that the surface,with a thin shared layer of the fluid on it,oscillates in a harmonic manner along the x-axis of the rivulet flow,which coincides with the main flow direction streaming down the underlying surface.We obtain the exact extension of the rivulet flow family,clarifying the structure of the pressure field,which fully absorbs the arising perturbation.The profile of the velocity field is assumed to be Gaussian-type with a non-zero level of plasticity.Hence,the absolutely non-Newtonian case of the viscoplastic flow solution,which satisfies the motion and continuity equations,is considered(with particular cases of exact solutions for pressure).The perturbed governing equations of motion for rivulet flows then result in the Riccati-type ordinary differential equation(ODE),describing the dynamics of the coordinate x(t).The approximated schematic dynamics are presented in graphical plots.
文摘Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forcing.They also underpin practical applications ranging from environmental transport to high-speed and aerothermal systems.Despite decades of progress,prediction remains difficult.The physics spans a wide range of scales and often couples turbulence,interphase momentum exchange,collisions,and interfacial transport.Reliable computation therefore requires both robust numerical methodology and careful physical interpretation.
文摘The present study aims at investigating the effect of temperature variation due to heat transfer between the formation and drilling fluids considering influx from the reservoir in the underbalanced drilling condition. Gas-liquid-solid three-phase flow model considering transient thermal interaction with the formation was applied to simulate wellbore fluid to calculate the wellbore temperature and pressure and analyze the influence of different parameters on fluid pressure and temperature distribution in annulus. The results show that the non-isothermal three-phase flow model with thermal consideration gives more accurate prediction of bottom-hole pressure(BHP) compared to other models considering geothermal temperature. Viscous dissipation, the heat produced by friction between the rotating drilling-string and well wall and drill bit drilling, and influx of oil and gas from reservoir have significant impact on the distribution of fluid temperature in the wellbore, which in turn affects the BHP. Bottom-hole fluid temperature decreases with increasing liquid flow rate, circulation time, and specific heat of liquid and gas but it increases with increasing in gas flow rate. It was found that BHP is strongly depended on the gas and liquid flow rates but it has weak dependence on the circulation time and specific heat of liquid and gas. BHP increase with increasing liquid flow rate and decreases with increasing gas flow rate.
基金supported in part by the National Key R&D Program of China(No.2024YFA1610700)the National Natural Science Foundation of China(No.12475147)。
文摘The Cooling-Storage-Ring External-target Experiment(CEE)at the Heavy Ion Research Facility in Lanzhou(HIRFL)is designed to study the properties of nuclear matter created in heavy-ion collisions at beam energies from a few hundred MeV/u up to 1 GeV/u.It aims to facilitate research on the quantum chromodynamics(QCD)phase structure in the high-baryondensity region.Collective flow is a fundamental observable in heavy-ion collision experiments,providing information on the bulk properties of the produced matter.Although the standard event plane method has been widely used to measure collective flow,it is still important to validate and optimize this method for the CEE spectrometer.In this paper,we study the experimental procedures for measuring directed flow in^(238)U+^(238)U collisions at 500 MeV/u,using event planes reconstructed by Multi-Wire Drift Chamber and Zero Degree Calorimeter,respectively.Jet AA Microscopic(JAM)transport generator is used to generate events,and the detector response is simulated by the CEE Fast Simulation(CFS)package.Finally,the optimal kinematic region for proton directed flow measurements is discussed for the future CEE experiment.
基金Project supported by the National Natural Science Foundation of China(Nos.12372214 and U2341231)。
文摘The Reynolds-averaged Navier-Stokes(RANS)technique enables critical engineering predictions and is widely adopted.However,since this iterative computation relies on the fixed-point iteration,it may converge to unexpected non-physical phase points in practice.We conduct an analysis on the phase-space characteristics and the fixed-point theory underlying the k-ε turbulence model,and employ the classical Kolmogorov flow as a framework,leveraging its direct numerical simulation(DNS)data to construct a one-dimensional(1D)system under periodic/fixed boundary conditions.The RANS results demonstrate that under periodic boundary conditions,the k-ε model exhibits only a unique trivial fixed point,with asymptotes capturing the phase portraits.The stability of this trivial fixed point is determined by a mathematically derived stability phase diagram,indicating the fact that the k-ε model will never converge to correct values under periodic conditions.In contrast,under fixed boundary conditions,the model can yield a stable non-trivial fixed point.The evolutionary mechanisms and their relationship with boundary condition settings systematically explain the inherent limitations of the k-ε model,i.e.,its deficiency in computing the flow field under periodic boundary conditions and sensitivity to boundary-value specifications under fixed boundary conditions.These conclusions are finally validated with the open-source code OpenFOAM.
