A numerical method was developed to directly simulate the compressible, particle-laden turbulent jets.The fourth order compact finite difference schemes were used to discretize the space derivatives. The Lagrangian me...A numerical method was developed to directly simulate the compressible, particle-laden turbulent jets.The fourth order compact finite difference schemes were used to discretize the space derivatives. The Lagrangian method was adopted to simulate the particle motion based on one-way coupling. It is found that the turbulent intensity profiles attain self-similar status in the jet downstream regions. At the Stokes number of 1, particles are concentrated largely in the outer boundaries of the large-scale vortex structures with the most uneven distribution and the widest dispersion in the lateral direction. Particles at the much smaller Stokes numbers are distributed evenly in the flow field, and the lateral dispersion is also considerable. Distribution of particles at much larger Stokes numbers is more uniform and the lateral dispersion becomes small. In addition, the inflow conditions have different effects on the particle dispersion. The direct numerical simulation (DNS) results accord with the previous experiments and numerical studies.展开更多
Airless spray painting, widely adopted for its efficiency and cost-effectiveness, generates a significant amount of airborne paint particles that contribute to air pollution and pose health risks to workers and nearby...Airless spray painting, widely adopted for its efficiency and cost-effectiveness, generates a significant amount of airborne paint particles that contribute to air pollution and pose health risks to workers and nearby residents. In this study, a paint particle dispersion reduction device (PPDRD) utilizing an axial cyclone separator and a high efficiency particulate air (HEPA) filter was designed and evaluated to minimize the dispersion of paint particles during airless spray applications. The cyclone separator captured larger paint particles through centrifugal force, while the HEPA filter effectively removed smaller particles that escaped the cyclone separator. Computational fluid dynamics (CFD) simulations were conducted to optimize key design parameters, including the number and height of guide vanes and suction flow rate. Lab-scale and field experiments demonstrated that the PPDRD significantly reduced airborne paint particles, with respirable particles (4 μm or smaller) decreasing by 50–80 % depending on particle size, while maintaining coating quality. These findings indicate that the PPDRD effectively mitigates the inhalation risks associated with hazardous paint aerosols, providing a practical solution for improving workplace safety and environmental compliance. This technology is expected to be widely applicable in exterior building painting, shipbuilding, and the automotive industry.展开更多
A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature, and is then used to study the effect of the area and point source loc...A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature, and is then used to study the effect of the area and point source locations on particle dispersion in displacement ventilation （DV） rooms. The results show that aerosol source location has a strong impact on the spatial distribution and removal rate of indoor particles. Particle removal performance depends strongly on ventilation efficiency and particle deposition rate on indoor surfaces. Important consideration for both relative ventilation efficiency and deposition rate consists of the position of the aerosol source relative to the main airflow pattern and the occupied zone.展开更多
The two-phase flow structure and particle dispersion for a dilute particle-laden jet in crossflow （JICF） were experimentally investigated by means of Phase Doppler Anemometry （PDA） measurement. The two-phase flow ...The two-phase flow structure and particle dispersion for a dilute particle-laden jet in crossflow （JICF） were experimentally investigated by means of Phase Doppler Anemometry （PDA） measurement. The two-phase flow experiments were conducted for different flow conditions and solid particle parameters, including the ratio of the jet velocity to crossflow velocity, the particle size and mass loading. The experimental results indicate that the fine particles with the size of 70 micron and the mass loading of 0.05% have a minor influence on the mean and fluctuation velocity fields of the two-phase JICF. However, the fine particle transport by the two-phase JICF is dominantly and preferentially affected by the shear layer vortices and exhibits a somewhat enhanced dispersion as compared to the fluid. For the coarse particles with the particle size ranging from 300 micron to 700 micron and the mass loading less than 0.16%, the effect of the particle parameters on the fluid phase is associated with both the anisotropic properties of the flow field and the trajectory deviation of the settling particles from the fluid. Compared to the single-phase JICF, the two-phase JICF laden with the coarse particles is recognized to possess more pronounced mean velocity alteration and turbulence modulation of the fluid phase in the presence of the particles with the larger particle size and higher mass loading.展开更多
The flow field in a semi-circular duct is simulated by Large Eddy Simulation(LES)and its particle field is simulated by Lagrange particle tracking method.Reynolds number Reb(based on bulk velocity and hydraulic diamet...The flow field in a semi-circular duct is simulated by Large Eddy Simulation(LES)and its particle field is simulated by Lagrange particle tracking method.Reynolds number Reb(based on bulk velocity and hydraulic diameter)is 80,000 and Ret(based on friction velocity and hydraulic diameter)is 3528.Particle diameter dpis chosen as 10,50,100,500 mm corresponding to St as 0.10,2.43,9.72,243.05.The results show that the intensity of the secondary flow near the ceiling is less than that near the floor because the ceiling is curved and able to inhibit the secondary flow.It is found that the difference between the semicircular duct and the square duct is that the secondary flow in a corner of the semi-circular duct is not symmetrical along the diagonal although they have the same generation mechanism.Regarding the particles,small particles(dp≤10 mm)are found to uniformly distribute in the duct,while large particles(dp≥50 mm)preferentially distribute in the corner and floor center.The maximum particles(dp=500mm)fall on the floor quickly and their dispersion mainly depends on the secondary flow near the floor.Particle deposition in the corner depends on particle size due to the effect of secondary flow and gravity.The effect of lift force on particles becomes more significant for 50 and 100 mm particles in comparison with other smaller particles.In the end,the effect of secondary flow is found to be more significant to dominate particle behavior than that of flow fluctuation.展开更多
The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated （DV） room were numerically modeled with validation by experimental data from the literature. T...The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated （DV） room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources （such as particles released from work activities in an office）. However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.展开更多
Mechanical and natural ventilations are effective measures to remove indoor airborne contaminants,thereby creating improved indoor air quality(IAQ).Among various simulation techniques,Markov chain model is a relativel...Mechanical and natural ventilations are effective measures to remove indoor airborne contaminants,thereby creating improved indoor air quality(IAQ).Among various simulation techniques,Markov chain model is a relatively new and efficient method in predicting indoor airborne pollutants.The existing Markov chain model(for indoor airborne pollutants)is basically assumed as first-order,which however is difficult to deal with airborne particles with non-negligible inertial.In this study,a novel weight-factor-based high-order(second-order and third-order)Markov chain model is developed to simulate particle dispersion and deposition indoors under fixed and dynamic ventilation modes.Flow fields under various ventilation modes are solved by computational fluid dynamics(CFD)tools in advance,and then the basic first-order Markov chain model is implemented and validated by both simulation results and experimental data from literature.Furthermore,different groups of weight factors are tested to estimate appropriate weight factors for both second-order and third-order Markov chain models.Finally,the calculation process is properly designed and controlled,so that the proposed high-order(second-order)Markov chain model can be used to perform particle-phase simulation under consecutively changed ventilation modes.Results indicate that the proposed second-order model does well in predicting particle dispersion and deposition under fixed ventilation mode as well as consecutively changed ventilation modes.Compared with traditional first-order Markov chain model,the proposed high-order model performs with more reasonable accuracy but without significant computing cost increment.The most suitable weight factors of the simulation case in this study are found to be(λ_(1)=0.7,λ_(2)=0.3,λ_(3)=0)for second-order Markov chain model,and(λ_(1)=0.8,λ_(2)=0.1,λ_(3)=0.1)for third-order Markov chain model in terms of reducing errors in particle deposition and escape prediction.With the improvements of the efficiency of state transfer matrix construction and flow field data acquisition/processing,the proposed high-order Markov chain model is expected to provide an alternative choice for fast prediction of indoor airborne particulate(as well as gaseous)pollutants under transient flows.展开更多
In this paper, the three_dimensional vo rtex filament method was used to simulate the evolution of vortex structures in the axisymmetric round jet. The results agree well with the ones given by Chung and Troutt. The...In this paper, the three_dimensional vo rtex filament method was used to simulate the evolution of vortex structures in the axisymmetric round jet. The results agree well with the ones given by Chung and Troutt. Then one_coupling model was employed to calculate the particle motio n based on the computed flows. The results show that the particle motion is affe cted by flows obviously at the case of particle number St1 and negligibly at St1 ,particles distribute around the vortex structures uniformly at St ～1 . When perturbations with wavenumber 5 are introduced to vortex rings, part icles disperse wider along radial direction, which conforms to the experimental results. The degree of particle dispersion is in the direct ratio to the amplitu de of perturbation. The conclusions given in the paper are useful to the practic e usage.展开更多
The present study considers the developing mixing layer that is formed bymerging of two free streams initially separated by a splitter plate. To investigate the influence ofthe vortical structures on the particle disp...The present study considers the developing mixing layer that is formed bymerging of two free streams initially separated by a splitter plate. To investigate the influence ofthe vortical structures on the particle dispersion, numerical simulation was conducted when thevelocity ratio, defined as R = U_∞ - U_(-∞)/U_∞ + U_(-∞), is 0. 5. Large-Eddy Simulation (LES)was employed to understand the effect of large-scale vortical structures originated by theKelvin-Helmholtz instability on the partical dispersion. The flyash with the particle sizes 10, 50,100, 150, and 200um respectively were loaded at the origin of the two-dimensional mixing layer. Itis confirmed that the particle dispersion depends strongly on the motion of large-scale vorticalstructures. The particle dispersion is visualized numerically by following the particle trajectoriesin the mixing layer undergoing pairing interaction.展开更多
In order to fabricate dispersion strengthened alloys strengthened by submicron-sized or nano-sized stable particles through casting routes, understanding of the formation process of dispersion strengthening particles ...In order to fabricate dispersion strengthened alloys strengthened by submicron-sized or nano-sized stable particles through casting routes, understanding of the formation process of dispersion strengthening particles in metal melt is of significance. Thus, nano NiO and TiO2 particles were selected as reactant to form in-situ dispersion strengthening oxide particles in Fe20Cr5Al alloy. Nano NiO and TiO2 particle powder was separately dispersed into nano Ni powder first. The loose mixed nano powder was added in Fe20CrSAl alloy melt when pouring the melt into mold. The study shows that nano NiO particles were not as effective as nano TiO2 particles in forming dispersion strengthening Al2O3 particles. The final diameters of dispersion strengthening oxide particles arose from nano TiO2 particles were of submicron. The Brownian collision of particles had caused this coarsening.展开更多
Fe_3O_4/PS magnetic particles with core/shell structure has been prepared in the presence of Fe3O4 magnetic fluid in ethanol/water mixture.Magnetic particles with diameter size range from 5. 54 t0 187. 32 μm were obt...Fe_3O_4/PS magnetic particles with core/shell structure has been prepared in the presence of Fe3O4 magnetic fluid in ethanol/water mixture.Magnetic particles with diameter size range from 5. 54 t0 187. 32 μm were obtained by different reaction conditions.Some parameters such as ethanol, PEG and monomer which affect particle size diameter and size distribution are discussed briefly in this paper.展开更多
The mechanism of the response motion of a suspended particle to turbulent motion of its surrounding fluid is different according to si:e of turbulent eddies. The particle is dragged by the viscous force of large eddie...The mechanism of the response motion of a suspended particle to turbulent motion of its surrounding fluid is different according to si:e of turbulent eddies. The particle is dragged by the viscous force of large eddies, and meanwhile driven randomly by small eddies. Based on this understanding, the dispersion of a particle with finite size in a homogeneous isotropic turbulence is calculated in this study. Results show that there are two competing effects: when enhanced by the inertia of a particle, the long-term particle diffusivity is reduced by the finite size of the particle.展开更多
Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The ...Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The dispersion relations for the waves are obtained. It is found that the frequencies of both the longitudinal and transverse dust waves increase with the density and when the density is sufficiently high a cutoff region appears at the short wavelength. With the increase of the particle number density, the common frequency tends to increase, and the sound speed of the longitudinal wave also increases, but that of the transverse wave remains low.展开更多
CO_(2)-responsive gels,which swell upon contact with CO_(2),are widely used for profile control to plug high-permeability gas flow channels in carbon capture,utilization,and storage(CCUS)applications in oil reser-voir...CO_(2)-responsive gels,which swell upon contact with CO_(2),are widely used for profile control to plug high-permeability gas flow channels in carbon capture,utilization,and storage(CCUS)applications in oil reser-voirs.However,the use of these gels in high-temperature CCUS applications is limited due to their rever-sible swelling behavior at elevated temperatures.In this study,a novel dispersed particle gel(DPG)suspension is developed for high-temperature profile control in CCUS applications.First,we synthesize a double-network hydrogel consisting of a crosslinked polyacrylamide(PAAm)network and a crosslinked sodium alginate(SA)network.The hydrogel is then sheared in water to form a pre-prepared DPG suspen-sion.To enhance its performance,the gel particles are modified by introducing potassium methylsilan-etriolate(PMS)upon CO_(2) exposure.Comparing the particle size distributions of the modified and pre-prepared DPG suspension reveals a significant swelling of gel particles,over twice their original size.Moreover,subjecting the new DPG suspension to a 100℃ environment for 24 h demonstrates that its gel particle sizes do not decrease,confirming irreversible swelling,which is a significant advantage over the traditional CO_(2)-responsive gels.Thermogravimetric analysis further indicates improved thermal sta-bility compared to the pre-prepared DPG particles.Core flooding experiments show that the new DPG suspension achieves a high plugging efficiency of 95.3%in plugging an ultra-high permeability sandpack,whereas the pre-prepared DPG suspension achieves only 82.8%.With its high swelling ratio,irreversible swelling at high temperatures,enhanced thermal stability,and superior plugging performance,the newly developed DPG suspension in this work presents a highly promising solution for profile control in high-temperature CCUS applications.展开更多
In order to understand the interaction between large-scale vortex structure and particles, a two-way coupling temporal mixing layer laden with particles at a Stokes number of 5 with different mass loading planted init...In order to understand the interaction between large-scale vortex structure and particles, a two-way coupling temporal mixing layer laden with particles at a Stokes number of 5 with different mass loading planted initially in the upper half region is numerically studied. The pseudospectral method is used for the flow fluid and the Lagrangian approach is employed to trace particles. The momentum coupling effect introduced by a particle is approximated to a point force. The simulation results show that the coherent structures are still dominant in the mixing layer, but the large-scale vortex structure and particle dispersion are modulated. The length of large-scale vortex structure is shortened and the pairing is delayed. At the same time, the particles are distributed more evenly in the whole flow field as the mass loading is increased, but the particle dispersion along the transverse direction differs from that along the spanwise direction, which indicates that the effect by the addition of particle on the spanwise large-scale vortex structure is different from the streamwise counterpart.展开更多
To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particleladen wake f...To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particleladen wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0. 15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures.展开更多
Particle-laden water flows past a circular cylinder were numerically investigated. The discrete vortex method （DVM） was employed to evaluate the unsteady water flow fields and a Lagrangian approach was applied for t...Particle-laden water flows past a circular cylinder were numerically investigated. The discrete vortex method （DVM） was employed to evaluate the unsteady water flow fields and a Lagrangian approach was applied for tracking individual solid particles. A dispersion function was defined to represent the dispersion scale of the particle. The wake vortex patterns, the distributions and the time series of dispersion functions of particles with different Stokes numbers were obtained. Numerical results show that the particle distribution in the wake of the circular cylinder is closely related to the particle＇s Stokes number and the structure of wake vortices： （1） the intermediate sized particles with Stokes numbers, St, of 0.25, 1.0 and 4.0 can not enter the vortex cores and concen- trate near the peripheries of the vortex structures, （2） in the circular cylinder wake, the dispersion intensity of particles decreases as St is increased from 0.25 to 4.0.展开更多
Gas solid two-phase turbulent plane jet is applied to many natural s it uations and in engineering systems. To predict the particle dispersion in the ga s jet is of great importance in industrial applications and in ...Gas solid two-phase turbulent plane jet is applied to many natural s it uations and in engineering systems. To predict the particle dispersion in the ga s jet is of great importance in industrial applications and in the designing of engineering systems. A large eddy simulation of the two-phase plane jet was con d ucted to investigate the particle dispersion patterns. The particles with Stokes numbers equal to 0 0028, 0 3, 2 5, 28 (corresponding to particle diameter 1 μm , 10 μm, 30 μm, 100 μm, respectively) in \%Re\%=11 300 gas flow were studied. The simulation results of gas phase motion agreed well with previous experimental re sults. And the simulation results of the solid particles motion showed that part icles with different Stokes number have different spatial dispersion; and that p articles with intermediate Stokes number have the largest dispersion ratio.展开更多
We reported an approach to reconstruct the complex phase morphology of impact polypropylene copolymer （IPC） with core-shell dispersed particles and to optimize its toughness in approximate shear condition. The molte...We reported an approach to reconstruct the complex phase morphology of impact polypropylene copolymer （IPC） with core-shell dispersed particles and to optimize its toughness in approximate shear condition. The molten-state annealing results indicate that the phase structure with core-shell dispersed particles is unstable and could be completely destroyed by static annealing, resulting in the degradation of impact strength. By using a co-rotating twin screw extruder, we found that the dispersed particle with core-shell structure could be rebuilt in appropriate condition with the recovery of excellent impact strength due to both the huge interfacial tension during solidification and the great difference in viscosity of components. Results reveal that almost all the extruded IPCs show the impact strength 60%-90% higher than that of annealed IPCs at room temperature. And the twice-extruded IPC shows the highest impact strength, 446% higher than that of IPC annealed for 30 min. As for low temperature tests, the impact strength of extruded IPCs also increases by 33%-58%. According to adjusting the processing conditions including extrusion speed, extrusion frequency and temperature, an optimization of toughness was well established.展开更多
Micro-scale and nano-scale dispersed gel particles(DPG)are capable of deep migration in oil reservoirs due to their deformability,viscoelasticity,and suitable particle size.Therefore,it has been widely studied and app...Micro-scale and nano-scale dispersed gel particles(DPG)are capable of deep migration in oil reservoirs due to their deformability,viscoelasticity,and suitable particle size.Therefore,it has been widely studied and applied in reservoir conformance control in recent years.However,for highly permeable channels,their plugging performance is still limited.In addition,conventional in situ cross-linked polymer gels(ISCPGs)have fast gelation time under extremely high-temperature conditions,which often causes problems such as difficulty in pumping.Therefore,a re-cross linkable dispersed particle gel(RDPG)system applied for conformance control in highly permeable channels of extremely high-temperature petroleum reservoirs was investigated.The particle size distribution,gelation time,gel strength,injection performance,and perfo rmance strength in po rous media were investigated using a laser particle size meter,the Sydansk bottle test method,rheometer,and core displacement experiments,respectively.Results show that the RDPG suspension can be stable for more than 6 months at room temperature with storage modulus G’much lower than 10 Pa.It can pass through the pore throat by elastic deformation effect and does not cause strong blockage.Moreover,it can undergo re-crosslinking reaction at 150℃to form a strong bulk gel.The gel strength G’of re-crosslinked RDPG can be as high as 69.3 Pa,which meets the strength requirement of conformance control.The RDPG suspension has the properties of easy injection,and it also has strong plugging,and high-temperature resistance after re-crosslinked in the core,which can be a very promising material for conformance improvement in extremely high-temperature reservoirs.展开更多
基金Supported by the Natural Science Foundation of Zhejiang Province (No. 502047 and No. M503094)National Basic Research Program of China (No. 2003CB214500).
文摘A numerical method was developed to directly simulate the compressible, particle-laden turbulent jets.The fourth order compact finite difference schemes were used to discretize the space derivatives. The Lagrangian method was adopted to simulate the particle motion based on one-way coupling. It is found that the turbulent intensity profiles attain self-similar status in the jet downstream regions. At the Stokes number of 1, particles are concentrated largely in the outer boundaries of the large-scale vortex structures with the most uneven distribution and the widest dispersion in the lateral direction. Particles at the much smaller Stokes numbers are distributed evenly in the flow field, and the lateral dispersion is also considerable. Distribution of particles at much larger Stokes numbers is more uniform and the lateral dispersion becomes small. In addition, the inflow conditions have different effects on the particle dispersion. The direct numerical simulation (DNS) results accord with the previous experiments and numerical studies.
基金the“Reduction Management Program of Fine Dust Blind-Spots”and supported by the Ministry of Environment as part of the Korea Environmental Industry and Technology Institute(grant No.2020003060010)supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(grant No.RS-2024-00346834).
文摘Airless spray painting, widely adopted for its efficiency and cost-effectiveness, generates a significant amount of airborne paint particles that contribute to air pollution and pose health risks to workers and nearby residents. In this study, a paint particle dispersion reduction device (PPDRD) utilizing an axial cyclone separator and a high efficiency particulate air (HEPA) filter was designed and evaluated to minimize the dispersion of paint particles during airless spray applications. The cyclone separator captured larger paint particles through centrifugal force, while the HEPA filter effectively removed smaller particles that escaped the cyclone separator. Computational fluid dynamics (CFD) simulations were conducted to optimize key design parameters, including the number and height of guide vanes and suction flow rate. Lab-scale and field experiments demonstrated that the PPDRD significantly reduced airborne paint particles, with respirable particles (4 μm or smaller) decreasing by 50–80 % depending on particle size, while maintaining coating quality. These findings indicate that the PPDRD effectively mitigates the inhalation risks associated with hazardous paint aerosols, providing a practical solution for improving workplace safety and environmental compliance. This technology is expected to be widely applicable in exterior building painting, shipbuilding, and the automotive industry.
基金the National Natural Science Foundation of China(Grant No.50578034)Shanghai Educational Development Foundation,titled"Shuguang Project",PR.China(Grant No.03SG30).
文摘A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature, and is then used to study the effect of the area and point source locations on particle dispersion in displacement ventilation （DV） rooms. The results show that aerosol source location has a strong impact on the spatial distribution and removal rate of indoor particles. Particle removal performance depends strongly on ventilation efficiency and particle deposition rate on indoor surfaces. Important consideration for both relative ventilation efficiency and deposition rate consists of the position of the aerosol source relative to the main airflow pattern and the occupied zone.
基金supported by the National Natural Science Foundation of China (Grant Nos.10572084,10972134)the Specialized Research Fund for the Doctoral Program of Higher Education (Grant No.20050280008)
文摘The two-phase flow structure and particle dispersion for a dilute particle-laden jet in crossflow （JICF） were experimentally investigated by means of Phase Doppler Anemometry （PDA） measurement. The two-phase flow experiments were conducted for different flow conditions and solid particle parameters, including the ratio of the jet velocity to crossflow velocity, the particle size and mass loading. The experimental results indicate that the fine particles with the size of 70 micron and the mass loading of 0.05% have a minor influence on the mean and fluctuation velocity fields of the two-phase JICF. However, the fine particle transport by the two-phase JICF is dominantly and preferentially affected by the shear layer vortices and exhibits a somewhat enhanced dispersion as compared to the fluid. For the coarse particles with the particle size ranging from 300 micron to 700 micron and the mass loading less than 0.16%, the effect of the particle parameters on the fluid phase is associated with both the anisotropic properties of the flow field and the trajectory deviation of the settling particles from the fluid. Compared to the single-phase JICF, the two-phase JICF laden with the coarse particles is recognized to possess more pronounced mean velocity alteration and turbulence modulation of the fluid phase in the presence of the particles with the larger particle size and higher mass loading.
基金supported by National Natural Science Foundation of China(No.51876221,51776225)High-end Foreign Expert Introduction Project(G20190001270,B18054)。
文摘The flow field in a semi-circular duct is simulated by Large Eddy Simulation(LES)and its particle field is simulated by Lagrange particle tracking method.Reynolds number Reb(based on bulk velocity and hydraulic diameter)is 80,000 and Ret(based on friction velocity and hydraulic diameter)is 3528.Particle diameter dpis chosen as 10,50,100,500 mm corresponding to St as 0.10,2.43,9.72,243.05.The results show that the intensity of the secondary flow near the ceiling is less than that near the floor because the ceiling is curved and able to inhibit the secondary flow.It is found that the difference between the semicircular duct and the square duct is that the secondary flow in a corner of the semi-circular duct is not symmetrical along the diagonal although they have the same generation mechanism.Regarding the particles,small particles(dp≤10 mm)are found to uniformly distribute in the duct,while large particles(dp≥50 mm)preferentially distribute in the corner and floor center.The maximum particles(dp=500mm)fall on the floor quickly and their dispersion mainly depends on the secondary flow near the floor.Particle deposition in the corner depends on particle size due to the effect of secondary flow and gravity.The effect of lift force on particles becomes more significant for 50 and 100 mm particles in comparison with other smaller particles.In the end,the effect of secondary flow is found to be more significant to dominate particle behavior than that of flow fluctuation.
基金supported by the National Natural Science Foundation of China (Grant No. 40975093)Shanghai Educational Development Foundation titled "Shuguang Project", P.R. China(Grant No. 03SG30)
文摘The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated （DV） room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources （such as particles released from work activities in an office）. However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.
基金The investigation was supported by the National Science&Technology Supporting Program(No.2015BAJ03B00)the Natural Science Foundation of Hunan Province(Youth Program)(No.2021JJ40591)+1 种基金the Doctoral Scientific Research Foundation of Changsha University of Science and Technology(No.097/000301518)the Scientific Research Project of Hunan Provincial Department of Education(No.20C0033).
文摘Mechanical and natural ventilations are effective measures to remove indoor airborne contaminants,thereby creating improved indoor air quality(IAQ).Among various simulation techniques,Markov chain model is a relatively new and efficient method in predicting indoor airborne pollutants.The existing Markov chain model(for indoor airborne pollutants)is basically assumed as first-order,which however is difficult to deal with airborne particles with non-negligible inertial.In this study,a novel weight-factor-based high-order(second-order and third-order)Markov chain model is developed to simulate particle dispersion and deposition indoors under fixed and dynamic ventilation modes.Flow fields under various ventilation modes are solved by computational fluid dynamics(CFD)tools in advance,and then the basic first-order Markov chain model is implemented and validated by both simulation results and experimental data from literature.Furthermore,different groups of weight factors are tested to estimate appropriate weight factors for both second-order and third-order Markov chain models.Finally,the calculation process is properly designed and controlled,so that the proposed high-order(second-order)Markov chain model can be used to perform particle-phase simulation under consecutively changed ventilation modes.Results indicate that the proposed second-order model does well in predicting particle dispersion and deposition under fixed ventilation mode as well as consecutively changed ventilation modes.Compared with traditional first-order Markov chain model,the proposed high-order model performs with more reasonable accuracy but without significant computing cost increment.The most suitable weight factors of the simulation case in this study are found to be(λ_(1)=0.7,λ_(2)=0.3,λ_(3)=0)for second-order Markov chain model,and(λ_(1)=0.8,λ_(2)=0.1,λ_(3)=0.1)for third-order Markov chain model in terms of reducing errors in particle deposition and escape prediction.With the improvements of the efficiency of state transfer matrix construction and flow field data acquisition/processing,the proposed high-order Markov chain model is expected to provide an alternative choice for fast prediction of indoor airborne particulate(as well as gaseous)pollutants under transient flows.
文摘In this paper, the three_dimensional vo rtex filament method was used to simulate the evolution of vortex structures in the axisymmetric round jet. The results agree well with the ones given by Chung and Troutt. Then one_coupling model was employed to calculate the particle motio n based on the computed flows. The results show that the particle motion is affe cted by flows obviously at the case of particle number St1 and negligibly at St1 ,particles distribute around the vortex structures uniformly at St ～1 . When perturbations with wavenumber 5 are introduced to vortex rings, part icles disperse wider along radial direction, which conforms to the experimental results. The degree of particle dispersion is in the direct ratio to the amplitu de of perturbation. The conclusions given in the paper are useful to the practic e usage.
文摘The present study considers the developing mixing layer that is formed bymerging of two free streams initially separated by a splitter plate. To investigate the influence ofthe vortical structures on the particle dispersion, numerical simulation was conducted when thevelocity ratio, defined as R = U_∞ - U_(-∞)/U_∞ + U_(-∞), is 0. 5. Large-Eddy Simulation (LES)was employed to understand the effect of large-scale vortical structures originated by theKelvin-Helmholtz instability on the partical dispersion. The flyash with the particle sizes 10, 50,100, 150, and 200um respectively were loaded at the origin of the two-dimensional mixing layer. Itis confirmed that the particle dispersion depends strongly on the motion of large-scale vorticalstructures. The particle dispersion is visualized numerically by following the particle trajectoriesin the mixing layer undergoing pairing interaction.
基金Item Sponsored by International Co-operation Project (20061415)
文摘In order to fabricate dispersion strengthened alloys strengthened by submicron-sized or nano-sized stable particles through casting routes, understanding of the formation process of dispersion strengthening particles in metal melt is of significance. Thus, nano NiO and TiO2 particles were selected as reactant to form in-situ dispersion strengthening oxide particles in Fe20Cr5Al alloy. Nano NiO and TiO2 particle powder was separately dispersed into nano Ni powder first. The loose mixed nano powder was added in Fe20CrSAl alloy melt when pouring the melt into mold. The study shows that nano NiO particles were not as effective as nano TiO2 particles in forming dispersion strengthening Al2O3 particles. The final diameters of dispersion strengthening oxide particles arose from nano TiO2 particles were of submicron. The Brownian collision of particles had caused this coarsening.
文摘Fe_3O_4/PS magnetic particles with core/shell structure has been prepared in the presence of Fe3O4 magnetic fluid in ethanol/water mixture.Magnetic particles with diameter size range from 5. 54 t0 187. 32 μm were obtained by different reaction conditions.Some parameters such as ethanol, PEG and monomer which affect particle size diameter and size distribution are discussed briefly in this paper.
文摘The mechanism of the response motion of a suspended particle to turbulent motion of its surrounding fluid is different according to si:e of turbulent eddies. The particle is dragged by the viscous force of large eddies, and meanwhile driven randomly by small eddies. Based on this understanding, the dispersion of a particle with finite size in a homogeneous isotropic turbulence is calculated in this study. Results show that there are two competing effects: when enhanced by the inertia of a particle, the long-term particle diffusivity is reduced by the finite size of the particle.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11675261 and 21403297the Scientific Research Foundation of Ludong University under Grant No LY2014010
文摘Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The dispersion relations for the waves are obtained. It is found that the frequencies of both the longitudinal and transverse dust waves increase with the density and when the density is sufficiently high a cutoff region appears at the short wavelength. With the increase of the particle number density, the common frequency tends to increase, and the sound speed of the longitudinal wave also increases, but that of the transverse wave remains low.
基金Lin Du acknowledges the financial support provided by China Scholarship Council(CSC)via a Ph.D.Scholarship(202008510128)supported by Core Technology Project of China National Petroleum Corporation(CNPC)"Research on Thermal Miscible Flooding Technology"(2023ZG18)。
文摘CO_(2)-responsive gels,which swell upon contact with CO_(2),are widely used for profile control to plug high-permeability gas flow channels in carbon capture,utilization,and storage(CCUS)applications in oil reser-voirs.However,the use of these gels in high-temperature CCUS applications is limited due to their rever-sible swelling behavior at elevated temperatures.In this study,a novel dispersed particle gel(DPG)suspension is developed for high-temperature profile control in CCUS applications.First,we synthesize a double-network hydrogel consisting of a crosslinked polyacrylamide(PAAm)network and a crosslinked sodium alginate(SA)network.The hydrogel is then sheared in water to form a pre-prepared DPG suspen-sion.To enhance its performance,the gel particles are modified by introducing potassium methylsilan-etriolate(PMS)upon CO_(2) exposure.Comparing the particle size distributions of the modified and pre-prepared DPG suspension reveals a significant swelling of gel particles,over twice their original size.Moreover,subjecting the new DPG suspension to a 100℃ environment for 24 h demonstrates that its gel particle sizes do not decrease,confirming irreversible swelling,which is a significant advantage over the traditional CO_(2)-responsive gels.Thermogravimetric analysis further indicates improved thermal sta-bility compared to the pre-prepared DPG particles.Core flooding experiments show that the new DPG suspension achieves a high plugging efficiency of 95.3%in plugging an ultra-high permeability sandpack,whereas the pre-prepared DPG suspension achieves only 82.8%.With its high swelling ratio,irreversible swelling at high temperatures,enhanced thermal stability,and superior plugging performance,the newly developed DPG suspension in this work presents a highly promising solution for profile control in high-temperature CCUS applications.
基金Supported by the National Natural Science Foundation of China (No. 50236030, No. 50076038) and the Major State Basic Research Development Program of China (No. G19990222).
文摘In order to understand the interaction between large-scale vortex structure and particles, a two-way coupling temporal mixing layer laden with particles at a Stokes number of 5 with different mass loading planted initially in the upper half region is numerically studied. The pseudospectral method is used for the flow fluid and the Lagrangian approach is employed to trace particles. The momentum coupling effect introduced by a particle is approximated to a point force. The simulation results show that the coherent structures are still dominant in the mixing layer, but the large-scale vortex structure and particle dispersion are modulated. The length of large-scale vortex structure is shortened and the pairing is delayed. At the same time, the particles are distributed more evenly in the whole flow field as the mass loading is increased, but the particle dispersion along the transverse direction differs from that along the spanwise direction, which indicates that the effect by the addition of particle on the spanwise large-scale vortex structure is different from the streamwise counterpart.
文摘To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particleladen wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0. 15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures.
基金Project supported by the National Natural Science Foundation of China (No.70371011) the Science Development Foundation of Shanghai Municipal Commission of Education (No.03GK04)
文摘Particle-laden water flows past a circular cylinder were numerically investigated. The discrete vortex method （DVM） was employed to evaluate the unsteady water flow fields and a Lagrangian approach was applied for tracking individual solid particles. A dispersion function was defined to represent the dispersion scale of the particle. The wake vortex patterns, the distributions and the time series of dispersion functions of particles with different Stokes numbers were obtained. Numerical results show that the particle distribution in the wake of the circular cylinder is closely related to the particle＇s Stokes number and the structure of wake vortices： （1） the intermediate sized particles with Stokes numbers, St, of 0.25, 1.0 and 4.0 can not enter the vortex cores and concen- trate near the peripheries of the vortex structures, （2） in the circular cylinder wake, the dispersion intensity of particles decreases as St is increased from 0.25 to 4.0.
文摘Gas solid two-phase turbulent plane jet is applied to many natural s it uations and in engineering systems. To predict the particle dispersion in the ga s jet is of great importance in industrial applications and in the designing of engineering systems. A large eddy simulation of the two-phase plane jet was con d ucted to investigate the particle dispersion patterns. The particles with Stokes numbers equal to 0 0028, 0 3, 2 5, 28 (corresponding to particle diameter 1 μm , 10 μm, 30 μm, 100 μm, respectively) in \%Re\%=11 300 gas flow were studied. The simulation results of gas phase motion agreed well with previous experimental re sults. And the simulation results of the solid particles motion showed that part icles with different Stokes number have different spatial dispersion; and that p articles with intermediate Stokes number have the largest dispersion ratio.
基金financially supported by the National Natural Science Foundation of China(Nos.51173157 and 51173165)the Fundamental Research Funds for the Central Universities(No.2013QNA4048)
文摘We reported an approach to reconstruct the complex phase morphology of impact polypropylene copolymer （IPC） with core-shell dispersed particles and to optimize its toughness in approximate shear condition. The molten-state annealing results indicate that the phase structure with core-shell dispersed particles is unstable and could be completely destroyed by static annealing, resulting in the degradation of impact strength. By using a co-rotating twin screw extruder, we found that the dispersed particle with core-shell structure could be rebuilt in appropriate condition with the recovery of excellent impact strength due to both the huge interfacial tension during solidification and the great difference in viscosity of components. Results reveal that almost all the extruded IPCs show the impact strength 60%-90% higher than that of annealed IPCs at room temperature. And the twice-extruded IPC shows the highest impact strength, 446% higher than that of IPC annealed for 30 min. As for low temperature tests, the impact strength of extruded IPCs also increases by 33%-58%. According to adjusting the processing conditions including extrusion speed, extrusion frequency and temperature, an optimization of toughness was well established.
基金supported by the Research Foundation of China University of Petroleum-Beijing at Karamay(No.XQZX20200010)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2019D01B57)+2 种基金the Tianshan Talent Project(No.2019Q025)the Sichuan Province Regional Innovation Cooperation Project(No.2020YFQ0036)the CNPC Strategic Cooperation Science and Technology Project(ZLZX2020-01-04-04)
文摘Micro-scale and nano-scale dispersed gel particles(DPG)are capable of deep migration in oil reservoirs due to their deformability,viscoelasticity,and suitable particle size.Therefore,it has been widely studied and applied in reservoir conformance control in recent years.However,for highly permeable channels,their plugging performance is still limited.In addition,conventional in situ cross-linked polymer gels(ISCPGs)have fast gelation time under extremely high-temperature conditions,which often causes problems such as difficulty in pumping.Therefore,a re-cross linkable dispersed particle gel(RDPG)system applied for conformance control in highly permeable channels of extremely high-temperature petroleum reservoirs was investigated.The particle size distribution,gelation time,gel strength,injection performance,and perfo rmance strength in po rous media were investigated using a laser particle size meter,the Sydansk bottle test method,rheometer,and core displacement experiments,respectively.Results show that the RDPG suspension can be stable for more than 6 months at room temperature with storage modulus G’much lower than 10 Pa.It can pass through the pore throat by elastic deformation effect and does not cause strong blockage.Moreover,it can undergo re-crosslinking reaction at 150℃to form a strong bulk gel.The gel strength G’of re-crosslinked RDPG can be as high as 69.3 Pa,which meets the strength requirement of conformance control.The RDPG suspension has the properties of easy injection,and it also has strong plugging,and high-temperature resistance after re-crosslinked in the core,which can be a very promising material for conformance improvement in extremely high-temperature reservoirs.
