The Basset-Boussinesq-Oseen （BBO） equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to th...The Basset-Boussinesq-Oseen （BBO） equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to the impeller rotation, as additional effects. This paper firstly reviews various approximations of the BBO equation for the motion of dispersion particles in a viscous fluid. Then based on the motion equation for particles in low Reynolds number centrifugal pumps, a formula for calculating the tracking characteristics of tracer particles is deduced through the Fourier integral transformation. After that the deviations of the particle motion from the fluid motion, as predicted by the various approximations, are discussed and compared. At last, with an emphasis on the Particle Image Velocimetry （PIV） results, the tracking characteristics of particles are estimated. Also, advantages and disadvantages of different tracer particles are discussed and suitable tracer particles for application in PIV studies for flow fields in centrifugal pumps are suggested.展开更多
Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have report...Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall （z = 0.25-1.5 μm） with two sizes of tracer particles （φ 50 nm and φ200 nm）. The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.展开更多
A finite element model based on solid mechanics was developed with ABAQUS to study the material flow in wholeprocess of friction stir welding （FSW）, with the technique of tracer particles. Simulation results indicat...A finite element model based on solid mechanics was developed with ABAQUS to study the material flow in wholeprocess of friction stir welding （FSW）, with the technique of tracer particles. Simulation results indicate that the flow pattern of thetracer particles around the pin is spiral movement. There are very different flow patterns at the upper and lower parts of the weld. Thematerial on the upper surface has the spiral downward movement that is affected by the shoulder and the lower material has the spiralupward movement that is affected by the pin. The velocity of the material flow on the periphery of the stirring pin is higher than thatat the bottom of the stirring pin. The material can be rotated with a stirring pin a few times, agreeing well with the previousexperimental observation by tungsten tracer particles.展开更多
Lateral solid mixing was investigated experimentally in the dense zone of a 900mm×100mm×5.2m rectangular circulating fluidized bed riser.Using heated tracer injection,the lateral solid dispersion was determ...Lateral solid mixing was investigated experimentally in the dense zone of a 900mm×100mm×5.2m rectangular circulating fluidized bed riser.Using heated tracer injection,the lateral solid dispersion was determined by measuring the temperature response at different lateral positions. Furthermore, a one-dimensional dispersion model,which describes the solid mixing in the dense zone,is presented.The experimental results were used to determine the lateral particle dispersion coefficient under various operating conditions. A correlation of dispersion coefficient with bed height, gas velocity,and particle size is also proposed.展开更多
The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element m...The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element method. Three dimensional isothermal flow field of U-PVC in two kinds of TSE was calculated. The mixing performance of the screw elements of the extruders was statistically analyzed by particle tracking method. The dispersive mixing performance was characterized by the mixing index, the logarithm of stretching, and the segregation scale. The distributive mixing per forulance was characterized by the resident time distribution. The results indicate that the counter rotating TSE can build higher pressure and generate higher axial velocity and shear rate, whereas the co rotating TSE has better performance in dispersive and distributive mixing.展开更多
Early studies on Rayleigh−Taylor instability(RTI)primarily relied on the Navier−Stokes(NS)model.As research progresses,it becomes increasingly evident that the kinetic information that the NS model failed to capture i...Early studies on Rayleigh−Taylor instability(RTI)primarily relied on the Navier−Stokes(NS)model.As research progresses,it becomes increasingly evident that the kinetic information that the NS model failed to capture is of great value for identifying and even controlling the RTI process;simultaneously,the lack of analysis techniques for complex physical fields results in a significant waste of data information.In addition,early RTI studies mainly focused on the incompressible case and the weakly compressible case.In the case of strong compressibility,the density of the fluid from the upper layer(originally heavy fluid)may become smaller than that of the surrounding(originally light)fluid,thus invalidating the early method of distinguishing light and heavy fluids based on density.In this paper,tracer particles are incorporated into a single-fluid discrete Boltzmann method(DBM)model that considers the van der Waals potential.By using tracer particles to label the matter-particle sources,a careful study of the matter-mixing and energy-mixing processes of the RTI evolution is realized in the single-fluid framework.The effects of compressibility on the evolution of RTI are examined mainly through the analysis of bubble and spike velocities,the ratio of area occupied by heavy fluid,and various entropy generation rates of the system.It is demonstrated that:(i)compressibility has a suppressive effect on the spike velocity,and this suppressive impact diminishes as the Atwood number(At)increases.The influence of compressibility on bubble velocity shows a staged behavior with increasing.(ii)The impact of compressibility on the entropy production rate associated with the heat flow(S_(NOEF))is related to the stages of RTI evolution.Moreover,this staged impact of compressibility on S_(NOEF)varies with At.Compressibility exhibits an inhibitory effect on the entropy production rate associated with viscous stresses(S_(NOEF)).(iii)By incorporating the morphological parameter of the proportion of area occupied by heavy fluid(A_(h)),it is observed that the first minimum point of dAt/dt can serve as a criterion for identifying the point at which bubble velocity reaches its first maximum value.The series of physical cognition provides a more accurate understanding of the RTI kinetics and a helpful reference for the development of corresponding regulation techniques.展开更多
Efficient fluid mixing is essential for process intensification.This study proposes a new method in which gas-rigid-flexible composite blades are coupled to enhance chaotic mixing in multiphase flow systems.The rigidi...Efficient fluid mixing is essential for process intensification.This study proposes a new method in which gas-rigid-flexible composite blades are coupled to enhance chaotic mixing in multiphase flow systems.The rigidity and flexibility of the blades were adjusted by intermittent gas injection,which increased the effectiveness of mixing of the liquid-liquid two-phase fluid.This study investigates the influence of different process parameters on the mixing efficiency and quantifies the chaotic characteristics of fluid mixing through pressure-time series analysis of multiscale entropy and the 0–1 test.A high-speed camera recorded the bubble movement in the flow field,while particle image velocimetry(PIV)revealed the enhancement of the properties of the flow field in the system due to the suspended motion of the particles.Using suitable process parameters,gas-rigid-flexible composite blade coupling significantly enhanced the mixing effect,where the mixing time of the G-RFCP system was reduced by 1.42 times compared to that of the CP system.Bubble motion,deformation,and rupture enhanced the mechanical agitation,increasing the intensity of the turbulence and chaotic behaviour.Flow-field analysis indicated a three-fold increase in the vorticity and a 1.04-fold increase in the velocity difference for the G-RFCP system compared with those of the CP system.This study provides theoretical and experimental foundations for understanding chaotic mixing in liquid-liquid two-phase fluids.展开更多
基金supported by the National Outstanding Young Scientist Funds of China (Grant No.50825902)the Jiangsu Provincial Innovative Scholars "Climbing" Project of China(Grant No.BK2009006)the National Natural Science Foundation of China (Grant No.50979034)
文摘The Basset-Boussinesq-Oseen （BBO） equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to the impeller rotation, as additional effects. This paper firstly reviews various approximations of the BBO equation for the motion of dispersion particles in a viscous fluid. Then based on the motion equation for particles in low Reynolds number centrifugal pumps, a formula for calculating the tracking characteristics of tracer particles is deduced through the Fourier integral transformation. After that the deviations of the particle motion from the fluid motion, as predicted by the various approximations, are discussed and compared. At last, with an emphasis on the Particle Image Velocimetry （PIV） results, the tracking characteristics of particles are estimated. Also, advantages and disadvantages of different tracer particles are discussed and suitable tracer particles for application in PIV studies for flow fields in centrifugal pumps are suggested.
基金supported by the National Natural Science Foundation of China (10872203)the National Basic Research Program(2007AC744701)the CAS Research and Development Program of China (KSCX2-YW-H18)
文摘Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall （z = 0.25-1.5 μm） with two sizes of tracer particles （φ 50 nm and φ200 nm）. The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.
基金Projects(51331008,51405310,51401219)supported by the National Natural Science Foundation of China
文摘A finite element model based on solid mechanics was developed with ABAQUS to study the material flow in wholeprocess of friction stir welding （FSW）, with the technique of tracer particles. Simulation results indicate that the flow pattern of thetracer particles around the pin is spiral movement. There are very different flow patterns at the upper and lower parts of the weld. Thematerial on the upper surface has the spiral downward movement that is affected by the shoulder and the lower material has the spiralupward movement that is affected by the pin. The velocity of the material flow on the periphery of the stirring pin is higher than thatat the bottom of the stirring pin. The material can be rotated with a stirring pin a few times, agreeing well with the previousexperimental observation by tungsten tracer particles.
文摘Lateral solid mixing was investigated experimentally in the dense zone of a 900mm×100mm×5.2m rectangular circulating fluidized bed riser.Using heated tracer injection,the lateral solid dispersion was determined by measuring the temperature response at different lateral positions. Furthermore, a one-dimensional dispersion model,which describes the solid mixing in the dense zone,is presented.The experimental results were used to determine the lateral particle dispersion coefficient under various operating conditions. A correlation of dispersion coefficient with bed height, gas velocity,and particle size is also proposed.
基金Supported by the Industrial Foundation(20091041038)
文摘The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element method. Three dimensional isothermal flow field of U-PVC in two kinds of TSE was calculated. The mixing performance of the screw elements of the extruders was statistically analyzed by particle tracking method. The dispersive mixing performance was characterized by the mixing index, the logarithm of stretching, and the segregation scale. The distributive mixing per forulance was characterized by the resident time distribution. The results indicate that the counter rotating TSE can build higher pressure and generate higher axial velocity and shear rate, whereas the co rotating TSE has better performance in dispersive and distributive mixing.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172061,12102397,and 12101064)the Opening Project of State Key Laboratory of Explosion Science and Safety Protection(Beijing Institute of Technology)(Grant No.KFJJ23-02M)+1 种基金the Foundation of National Key Laboratory of Shock Wave and Detonation Physics(Grant No.JCKYS2023212003)the 2023 Computational Physics Key Laboratory Youth Fund Sponsored Project(Grant No.6241A05QN23001).
文摘Early studies on Rayleigh−Taylor instability(RTI)primarily relied on the Navier−Stokes(NS)model.As research progresses,it becomes increasingly evident that the kinetic information that the NS model failed to capture is of great value for identifying and even controlling the RTI process;simultaneously,the lack of analysis techniques for complex physical fields results in a significant waste of data information.In addition,early RTI studies mainly focused on the incompressible case and the weakly compressible case.In the case of strong compressibility,the density of the fluid from the upper layer(originally heavy fluid)may become smaller than that of the surrounding(originally light)fluid,thus invalidating the early method of distinguishing light and heavy fluids based on density.In this paper,tracer particles are incorporated into a single-fluid discrete Boltzmann method(DBM)model that considers the van der Waals potential.By using tracer particles to label the matter-particle sources,a careful study of the matter-mixing and energy-mixing processes of the RTI evolution is realized in the single-fluid framework.The effects of compressibility on the evolution of RTI are examined mainly through the analysis of bubble and spike velocities,the ratio of area occupied by heavy fluid,and various entropy generation rates of the system.It is demonstrated that:(i)compressibility has a suppressive effect on the spike velocity,and this suppressive impact diminishes as the Atwood number(At)increases.The influence of compressibility on bubble velocity shows a staged behavior with increasing.(ii)The impact of compressibility on the entropy production rate associated with the heat flow(S_(NOEF))is related to the stages of RTI evolution.Moreover,this staged impact of compressibility on S_(NOEF)varies with At.Compressibility exhibits an inhibitory effect on the entropy production rate associated with viscous stresses(S_(NOEF)).(iii)By incorporating the morphological parameter of the proportion of area occupied by heavy fluid(A_(h)),it is observed that the first minimum point of dAt/dt can serve as a criterion for identifying the point at which bubble velocity reaches its first maximum value.The series of physical cognition provides a more accurate understanding of the RTI kinetics and a helpful reference for the development of corresponding regulation techniques.
基金supports by the National Natural Science Foundation of China(project No.52166004)National key research and development plan project(project No.2022YFC3902000)Yunnan Major Scientific and Technological Projects(grant Nos.202202AG050007,202202AG050002).
文摘Efficient fluid mixing is essential for process intensification.This study proposes a new method in which gas-rigid-flexible composite blades are coupled to enhance chaotic mixing in multiphase flow systems.The rigidity and flexibility of the blades were adjusted by intermittent gas injection,which increased the effectiveness of mixing of the liquid-liquid two-phase fluid.This study investigates the influence of different process parameters on the mixing efficiency and quantifies the chaotic characteristics of fluid mixing through pressure-time series analysis of multiscale entropy and the 0–1 test.A high-speed camera recorded the bubble movement in the flow field,while particle image velocimetry(PIV)revealed the enhancement of the properties of the flow field in the system due to the suspended motion of the particles.Using suitable process parameters,gas-rigid-flexible composite blade coupling significantly enhanced the mixing effect,where the mixing time of the G-RFCP system was reduced by 1.42 times compared to that of the CP system.Bubble motion,deformation,and rupture enhanced the mechanical agitation,increasing the intensity of the turbulence and chaotic behaviour.Flow-field analysis indicated a three-fold increase in the vorticity and a 1.04-fold increase in the velocity difference for the G-RFCP system compared with those of the CP system.This study provides theoretical and experimental foundations for understanding chaotic mixing in liquid-liquid two-phase fluids.
