The effects of mass concentration and injection pressure on the atomization characteristics of low-viscosity fuel spray are studied in a constant-volume chamber.Microscopic spray parameters are measured by laser diffr...The effects of mass concentration and injection pressure on the atomization characteristics of low-viscosity fuel spray are studied in a constant-volume chamber.Microscopic spray parameters are measured by laser diffraction at different axial and radial positions downstream of the nozzle.The results show that the atomization effect is inhibited linearly with the increase of mass concentration.The increase of injection pressure promotes the droplet breakup.However,the trend gradually weakens and becomes more noticeable at high concentrations.Comparing with the concentration,the influence of the injection pressure on the atomization characteristics is dominant.Although low concentration and high injection pressure can promote the droplet breakup,they also increase the probability of droplet collision,resulting in droplet aggregation.This is more evident in low-viscosity fuels.The droplet size increases in the axial direction owing to the aggregation.However,the diameter decreases in the radial direction owing to the outward deflection of small droplets caused by air turbulence and entrainment.In addition,the high-velocity airflow significantly promotes the droplet breakup near the nozzle and spray axis regions and inhibits the aggregation effect.However,the lower-viscosity fuels keep smaller droplet sizes and better atomization in the whole spraying process,which is easier to realize than the higher-viscosity fuels.Overall,low concentration,high injection pressure,and low viscosity of fuel have beneficial effects on the droplet breakup.This is very important for improving the atomization effect of fuel.展开更多
The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional meth...The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional method and presents an extended wet sieving method.The extended method uses both the steel sieves and the nylon filter cloth sieves.The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm,0.038 mm,0.014 mm,0.012 mm,0.0063 mm,0.004 mm,0.003 mm,0.002 mm,and 0.001 mm,respectively.The extended method uses five steps to separate the general soil into many material sub-groups of gravel,sand,silt and clay with known particle size ranges.The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups.The extended method is demonstrated with a general soil of completely decomposed granite(CDG)in Hong Kong,China.The silt and clay materials with different particle size ranges are further examined,checked and verified using stereomicroscopic observation,physical and chemical property tests.The results further confirm the correctness of the extended wet sieving method.展开更多
A liquid-solid circulating fluidized bed boiler is designed and built for visualization research by applying the fluidized bed heat transfer and fouling prevention technology to the water side of the boiler. Four type...A liquid-solid circulating fluidized bed boiler is designed and built for visualization research by applying the fluidized bed heat transfer and fouling prevention technology to the water side of the boiler. Four types of engineering plastic particles with different physical properties are selected as the solid working media. The effect of particle types on the fluidization and distribution of particles in the boiler is investigated under different feedwater flow rates and amount of added particles by using the charge couple device image measurement and acquisition system. The results show that all kinds of particles can't be normally fluidized and accumulate in the drum at low amount of added particles and feedwater flow rate. The particles with great density and low sphericity are more likely to accumulate. The average solid holdup in the riser tubes increases with the increase in feedwater flow rate and the amount of added particles. The non-uniform degree of particle distribution in the riser tubes generally decreases with the increase in feedwater flow rate and the amount of added particles. The particles with small density and settling velocity have high average solid holdup in the riser tubes under close sphericity. In generally,the smaller the density and settling velocity, the more uniform the particle distribution in the riser tubes.Three-dimensional diagrams of the non-uniform degree of particle distribution in the riser tubes of the boiler are established.展开更多
Particle-laden gas flows past a circular cylinder at the Reynolds number of 2×10^(5) were numerically investigated. The Discrete Vortex Method (DVM) was employed to evaluate the unsteady gas flow fields and a Lag...Particle-laden gas flows past a circular cylinder at the Reynolds number of 2×10^(5) were numerically investigated. The Discrete Vortex Method (DVM) was employed to evaluate the unsteady gas flow fields and a Lagrangian approach was applied for tracking individual solid particles. The vortex patterns and the distributions of particles with different Stokes numbers were obtained. Numerical results show that: (1) at small Stokes number (St=0.01) the particles move with the fluid and could be found evenly throughout the flow, (2) the regions around the vortex cores, where few particles exist, become wider as the stokes number of particles increases from 0.01 to 1.0, (3) at middle Stokes number (St=1.0, 10) centrifugal forces throw the particles out of the wake vortices, (4) at high Stokes number (St=100, 1000) the particles are not affected by the vortices,and their motion is determined by their inertia effects.展开更多
A meshless Element-Free Galerkin (EFG) method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the part...A meshless Element-Free Galerkin (EFG) method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the particle surfaces. The results show that meshless methods are capable of dealing with real particle collisions, thus are superior to most mesh-based methods in reflecting the fluidization process with frequent particle collisions and suitable void fractions. Particle distribution greatly influences the drag coefficients even for the same voidage, that is, there are large differences in the average drag coefficients between nonuniform and uniform particle distributions. Different compacting directions also have different regu- larities, so conventional formulas such as 'Wen and Yu' and 'Felice' models have some deviations in such nonuniform distributions. To evaluate the influence of the nonuniformity, the drag force in multiple particle systems was simulated by using nonuniformity coefficients, Cvx and Cvy, to quantitatively describe the nonuniform distribution in different directions. Drag force during fluidization can be successfully evaluated by the use of Cvx alone.展开更多
The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equat...The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration.Some results are compared with the experimental data.The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable,and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow.The changes of the particle number concentration M_(0) and the geometric mean diameter dg are more obvious in the core area of the jet,but less obvious in other areas.With the increase in the initial particle number concentration m00,the values of M_(0) and the standard deviation of the particle sizeσdecrease,but the value of d_(g) increases.The decrease in the initial particle diameter leads to the reduction of M_(0) andσand the increase in d_(g).With the increase in the Reynolds number,particles have few chances of collision,and hence the coagulation rate is reduced,leading to the increase in M_(0) andσand the decrease in d_(g).展开更多
Characteristics of internal microstructures have a strong impact on the properties of particulate reinforced metal composites.In the present work,we perform finite element simulations to elucidate fundamental mechanis...Characteristics of internal microstructures have a strong impact on the properties of particulate reinforced metal composites.In the present work,we perform finite element simulations to elucidate fundamental mechanisms involved in the ultraprecision orthogonal cutting of aluminum-based silicon carbide composites(SiCp/AI),with an emphasis on the influence of particle distribution characteristic.The SiCp/AI composite with a particle volume fraction of 25 vol%and a mean particle size of 10|im consists of randomly distributed polygon-shaped SiC particles,the elastic deformation and brittle failure of which are described by the brittle cracking model.Simulation results reveal that in addition to metal matrix tearing,cuttinginduced particle deformation in terms of dislodging,debonding,and cracking plays an important role in the microscopic deformation and correlated machining force variation and machined surface integrity.It is found that the standard deviation of particle size to the mean value has a strong influence on the machinability of microscopic particle-tool edge interactions and macroscopically observed machining results.The present work provides a guideline for the rational synthesis of particulate-reinforced metal composites with high machinability.展开更多
The particle size distribution of polymer always develops in emulsion polymerization systems,and certain key phenomena/mechanisms as well as properties of the final product are significantly affected by this distribut...The particle size distribution of polymer always develops in emulsion polymerization systems,and certain key phenomena/mechanisms as well as properties of the final product are significantly affected by this distribution.This review mainly focuses on the measurement methods of particle size distribution rather than average particle size during the emulsion polymerization process,including the existing off-line,on-line,and in-line measurement methods.Moreover,the principle,resolution,performance,advantages,and drawbacks of various methods for evaluating particle size distribution are contrasted and illustrated.Besides,several possible development directions or solutions of the in-line measurement technology are explored.展开更多
Polyaluminum chloride (PAC) was used as coagulant and suspended particles in kaolin water. Online instruments including turbidimeter and particle counter were used to monitor the flocculation process. An evaluation ...Polyaluminum chloride (PAC) was used as coagulant and suspended particles in kaolin water. Online instruments including turbidimeter and particle counter were used to monitor the flocculation process. An evaluation model for demonstrating the impact on the flocculation effect was established based on the multiple linear regression analysis method. The parameter of the index weight of channels quantitatively described how the variation of floc particle population in different size ranges cause the decrement of turbidity. The study showed that the floc particles in different size ranges contributed differently to the decrease of turbidity and that the index weight of channel could excellently indicate the impact degree of floc particles dynamic distribution on flocculation effect. Therefore, the parameter may significantly benefit the development of coagulation and sedimentation techniques as well as the optimal coagulant selection.展开更多
Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of t...Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of this paper is to suggest an appropriate method to assess internal erosion potential of gravelly soil.By analyzing the sensitivity of soil material to internal erosion,the variable(Dc15/df85)max and the content of coarse particles(Pc)are selected as the evaluation indexes(Dc15 and df85 are the diameters of 15%mass passing in the coarse component and 85%mass passing in the fine component,respectively).A series of gravelly soils with different particle size distributions are tested for internal erosion by the self-made permeameter.Based on the test results,an evaluation method for the internal erosion of gravelly soil is proposed.Gravelly soil is prone to internal erosion when 60%≤Pc<95%and(Dc15/df85)max≥9.5.The proposed method shows good accuracy in evaluating the internal erosion of 36 soil samples from other studies,which confirms the reliability of the method.The proposed method makes it possible to accurately assess internal erosion of gravelly soil,and an alternative method is provided for engineers to determine whether there is a risk of internal erosion in earth structures consisting of gravelly soil.展开更多
The weighted-sum-of-gray-gas(WSGG)model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures,such as the flame in aero-engi...The weighted-sum-of-gray-gas(WSGG)model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures,such as the flame in aero-engine combustor.The radiative transfer equation is solved by the finite volume method.The particle size is assumed to obey uniform distribution and logarithmic normal(L-N)distribution,respectively.Results reveal that when particle size obeys uniform distribution,increasing particle size with total particle volume fraction fvunchanged will result in the decreasing of the absolute value of radiative heat transfer properties,and the effect of ignoring particle scattering will also be weakened.Opposite conclusions can be obtained when total particle number concentration N0 is unchanged.Moreover,if particle size obeys L-N distribution,increasing the narrowness indexσor decreasing the characteristic diameter Dˉwith the total particle volume fraction fvunchanged will increase the absolute value of radiative heat transfer properties.With total particle number concentration N0 unchanged,opposite conclusions for radiative heat source and incident radiation terms can be obtained except for radiative heat flux term.As a whole,the effects of particle size on the radiative heat transfer in the high-temperature homogeneous gas-particle mixtures are complicated,and the particle scattering cannot be ignoring just according to the particle size.展开更多
Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle ma...Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities. Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.展开更多
Characterizing soil particle-size distribution is a key measure towards soil property.The purpose of this study was to evaluate the multifractal characteristics of soil particle-size distribution among different land-...Characterizing soil particle-size distribution is a key measure towards soil property.The purpose of this study was to evaluate the multifractal characteristics of soil particle-size distribution among different land-use from a purple soil catchment and to generalize the spatial variation trend of multifractal parameters across the catchment.A total of 84 soil samples were collected from four kinds of land use patterns(dry land,orchard,paddy,and forest)in an agricultural catchment in the Three Gorges Reservoir Region,China.The multifractal analysis method was applied to quantitatively characterize the soil particle size distribution.Six soil particle size distribution(PSD)multifractal parameters(D(0),D(1),D(2),(35)a(q),(35)f[a(q)],α(0))were computed.Additionally,a geostatistical analysis was employed to reveal the spatial differentiation and map the spatial distribution of these parameters.Evident multifractal characteristics were found.The trend of generalized dimension spectrum of four land use patterns was basically consistent with the range of 0.8 to 2.0.However,orchard showed the largest monotonic decline,while the forest demonstrated the smallest decrease.D(0)of the four land use patterns were ranked as:dry land<orchard<forest<paddy,the order of D(1)was:dry land<paddy<orchard<forest,D(2)presented a rand-size relationship as dry land<forest<paddy<orchard.Furthermore,all land-use patterns presented asΔf[α(q)]<0.The rand-size relationship ofα(0)was same as D(0).The best-fitting model for D(0),D(1),D(2)andΔf[α(q)]was spherical model,forΔα(q)was gaussian model,and forα(0)was exponential model with structure variance ratio was 1.03%,49.83%,0.84%,1.48%,22.20%and 10.60%,respectively.The results showed that soil particles of each land use pattern were distributed unevenly.The multifractal parameters under different land use have significant differences,except forΔα(q).Differences in the composition of soil particles lead to differences in the multifractal properties even though they belong to the same soil texture.Farming behavior may refine particles and enhance the heterogeneity of soil particle distribution.Our results provide an effective reference for quantifying the impact of human activities on soil system in the Three Gorges Reservoir region.展开更多
The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stabili...The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stability of the solution obtained from DDF method has been investigated through optimizing the coefficient matrix, introducing a damping factor and a least square treatment. All calculations were accomplished with a microcomputer. It was shown that the average deviations of the size distribution obtained are not larger than the assigned random errors to the scattering intensities as long as the corresponding requirements are satisfied.展开更多
An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has be...An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.展开更多
Based on the laser diffraction and Shifrin transform,the measurement method of particle size distribution has been improved extensively.While in real measurements,some noise peaks exist in the inversion data and are e...Based on the laser diffraction and Shifrin transform,the measurement method of particle size distribution has been improved extensively.While in real measurements,some noise peaks exist in the inversion data and are easily to be misread as particle distribution peaks.The improved method used a truncation function as a filter is hard to distinguish adjacent peaks.Here,by introducing the bimodal resolution criterion,the filter function is optimized,and to a quasi truncation function with the optimized filter function is studied to achieve optimal bimodal resolution and to remove noise peaks.This new quasi truncation function fits multimode distribution very well.By combining the quasi truncation function with Shifrin transform,noise peaks are removed well and the adjacent peaks are distinguished clearly.Finally,laser diffraction experiments are conducted and the particle size distribution is analyzed by adoping the method.The results show that the quasi truncation function has better bimodal resolution than the truncation function.Generally,by combining the quasi truncation function with the Shifrin transform,in particle size distribution measurements with laser diffraction,the bimodal resolution is greatly increased and the noise is removed well.And the results can restore the original distribution perfectly.Therefore,the new method with combination of the quasi truncation function and the Shifrin transform provides a feasible and effective way to measure the multimode particle size distribution by laser diffraction.展开更多
This paper deals with the preblem of existence and uniqueness of the stationary distributions (abbr., s. d.'s) for the processes constructed in [4] .The main results are stated in § 1. For the reader's co...This paper deals with the preblem of existence and uniqueness of the stationary distributions (abbr., s. d.'s) for the processes constructed in [4] .The main results are stated in § 1. For the reader's convenience we first restate the existence theorems (Theorem 1 and 2) of the processes given in [4]. Then two existence theorems (Theorem 3 and 4) and a uniqueness theorem (Theorem 5) for the s. d.'s of the processes are presented. The last result (Theorem 6), as an application of the previous ones, is about the Schlgl model which comes from nonequilibrium statisticali physics. The details of the proofs of Theorem 3—6 are given in § 2—4.展开更多
The effect of particle size distribution of alumina has been investigated for silica-free tabular alumina low cement castables( LCC). Three different combinations of alumina have been included in the matrix formulat...The effect of particle size distribution of alumina has been investigated for silica-free tabular alumina low cement castables( LCC). Three different combinations of alumina have been included in the matrix formulation of the castables. All the three combinations are composed of a bimodal reactive alumina and a fine ground monomodal reactive alumina. The first A1 and second A2 combinations are respectively composed of bimodal and monomodal aluminas from Alteo,with a different fine /coarse particles ratio for the bimodal alumina. The two Alteo combinations have been compared with a third combination C composed of a bimodal commercially available grade and a monomodal commercially available grade. Optimization of particle size packing has been performed for the three different formulations using the Dinger and Funk model. With this optimization,the two formulations based on Alteo material( PFR,PBR and PFR40) achieve the same level of performance in applicative tests( flowability,cold physical properties,mechanical resistance,crystalline phases,thermal shocks and corrosion) as reference solutions on the market.展开更多
Particle size, textural and surface characteristics influence some major technological properties of high siliceous aluminosilicate zeolite and sillicoaluminophosphate (SAPO) microporous materials. A comparative stu...Particle size, textural and surface characteristics influence some major technological properties of high siliceous aluminosilicate zeolite and sillicoaluminophosphate (SAPO) microporous materials. A comparative study was furnished for measuring surface characteristics, particle size and particle size distribution using particle size analyzer (PSA) and scanning electron microscope (SEM). The PSA is capable of measuring particle diameter in micron range. The results of these techniques for estimation of particle size were compared and correlated statistically. Student t-test and variance ratio test (F-test) methods were performed for the significance of results by the analysis of variance (ANONA) and multiple-range tests. Textural and surface characteristics were evaluated by Brunauer, Emmett & Teller (BET) volumetric technique and v-αs plotting method. The textural results shows that the external surface area and micropore volume of microporous materials were higher than those of the high siliceous zeolites and its zeotype materials.展开更多
Particle size distributions (PSDs) of bottom sediments in a coastal zone are generally multimodal due to the complexity of the dynamic environment. In this paper, bottom sediments along the deep channel of the Pearl...Particle size distributions (PSDs) of bottom sediments in a coastal zone are generally multimodal due to the complexity of the dynamic environment. In this paper, bottom sediments along the deep channel of the Pearl River Estuary (PRE) are used to understand the multimodal PSDs' characteristics and the corresponding depositional environment. The results of curve-fitting analysis indicate that the near-bottom sediments in the deep channel generally have a bimodal distribution with a fine component and a relatively coarse component. The particle size distribution of bimodal sediment samples can be expressed as the sum of two lognormal functions and the parameters for each component can be determined. At each station of the PRE, the fine component makes up less volume of the sediments and is relatively poorly sorted. The relatively coarse component, which is the major component of the sediments, is even more poorly sorted. The interrelations between the dynamics and particle size of the bottom sediment in the deep channel of the PRE have also been investigated by the field measurement and simulated data. The critical shear velocity and the shear velocity are calculated to study the stability of the deep channel. The results indicate that the critical shear velocity has a similar distribution over large part of the deep channel due to the similar particle size distribution of sediments. Based on a comparison between the critical shear velocities derived from sedimentary parameters and the shear velocities obtained by tidal currents, it is likely that the depositional area is mainly distributed in the northern part of the channel, while the southern part of the deep channel has to face higher erosion risk.展开更多
基金Project supported by the Young Scientists Fund of National Natural Science Foundation of China(Grant No.11802136).
文摘The effects of mass concentration and injection pressure on the atomization characteristics of low-viscosity fuel spray are studied in a constant-volume chamber.Microscopic spray parameters are measured by laser diffraction at different axial and radial positions downstream of the nozzle.The results show that the atomization effect is inhibited linearly with the increase of mass concentration.The increase of injection pressure promotes the droplet breakup.However,the trend gradually weakens and becomes more noticeable at high concentrations.Comparing with the concentration,the influence of the injection pressure on the atomization characteristics is dominant.Although low concentration and high injection pressure can promote the droplet breakup,they also increase the probability of droplet collision,resulting in droplet aggregation.This is more evident in low-viscosity fuels.The droplet size increases in the axial direction owing to the aggregation.However,the diameter decreases in the radial direction owing to the outward deflection of small droplets caused by air turbulence and entrainment.In addition,the high-velocity airflow significantly promotes the droplet breakup near the nozzle and spray axis regions and inhibits the aggregation effect.However,the lower-viscosity fuels keep smaller droplet sizes and better atomization in the whole spraying process,which is easier to realize than the higher-viscosity fuels.Overall,low concentration,high injection pressure,and low viscosity of fuel have beneficial effects on the droplet breakup.This is very important for improving the atomization effect of fuel.
基金The work described in this paper was partially supported by grants from the Research Grant Council of the Hong Kong Special Administrative Region,China(Project Nos.HKU 17207518 and R5037-18).
文摘The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional method and presents an extended wet sieving method.The extended method uses both the steel sieves and the nylon filter cloth sieves.The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm,0.038 mm,0.014 mm,0.012 mm,0.0063 mm,0.004 mm,0.003 mm,0.002 mm,and 0.001 mm,respectively.The extended method uses five steps to separate the general soil into many material sub-groups of gravel,sand,silt and clay with known particle size ranges.The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups.The extended method is demonstrated with a general soil of completely decomposed granite(CDG)in Hong Kong,China.The silt and clay materials with different particle size ranges are further examined,checked and verified using stereomicroscopic observation,physical and chemical property tests.The results further confirm the correctness of the extended wet sieving method.
基金supported by the open foundation of State Key Laboratory of Chemical Engineering (SKL–ChE–18B03)the Municipal Science and Technology Commission of Tianjin, China (2009ZCKFGX01900)。
文摘A liquid-solid circulating fluidized bed boiler is designed and built for visualization research by applying the fluidized bed heat transfer and fouling prevention technology to the water side of the boiler. Four types of engineering plastic particles with different physical properties are selected as the solid working media. The effect of particle types on the fluidization and distribution of particles in the boiler is investigated under different feedwater flow rates and amount of added particles by using the charge couple device image measurement and acquisition system. The results show that all kinds of particles can't be normally fluidized and accumulate in the drum at low amount of added particles and feedwater flow rate. The particles with great density and low sphericity are more likely to accumulate. The average solid holdup in the riser tubes increases with the increase in feedwater flow rate and the amount of added particles. The non-uniform degree of particle distribution in the riser tubes generally decreases with the increase in feedwater flow rate and the amount of added particles. The particles with small density and settling velocity have high average solid holdup in the riser tubes under close sphericity. In generally,the smaller the density and settling velocity, the more uniform the particle distribution in the riser tubes.Three-dimensional diagrams of the non-uniform degree of particle distribution in the riser tubes of the boiler are established.
文摘Particle-laden gas flows past a circular cylinder at the Reynolds number of 2×10^(5) were numerically investigated. The Discrete Vortex Method (DVM) was employed to evaluate the unsteady gas flow fields and a Lagrangian approach was applied for tracking individual solid particles. The vortex patterns and the distributions of particles with different Stokes numbers were obtained. Numerical results show that: (1) at small Stokes number (St=0.01) the particles move with the fluid and could be found evenly throughout the flow, (2) the regions around the vortex cores, where few particles exist, become wider as the stokes number of particles increases from 0.01 to 1.0, (3) at middle Stokes number (St=1.0, 10) centrifugal forces throw the particles out of the wake vortices, (4) at high Stokes number (St=100, 1000) the particles are not affected by the vortices,and their motion is determined by their inertia effects.
基金supported by the National Natural Science Foundation of China (No. 51076083)
文摘A meshless Element-Free Galerkin (EFG) method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the particle surfaces. The results show that meshless methods are capable of dealing with real particle collisions, thus are superior to most mesh-based methods in reflecting the fluidization process with frequent particle collisions and suitable void fractions. Particle distribution greatly influences the drag coefficients even for the same voidage, that is, there are large differences in the average drag coefficients between nonuniform and uniform particle distributions. Different compacting directions also have different regu- larities, so conventional formulas such as 'Wen and Yu' and 'Felice' models have some deviations in such nonuniform distributions. To evaluate the influence of the nonuniformity, the drag force in multiple particle systems was simulated by using nonuniformity coefficients, Cvx and Cvy, to quantitatively describe the nonuniform distribution in different directions. Drag force during fluidization can be successfully evaluated by the use of Cvx alone.
基金Project supported by the Major Program of the National Natural Science Foundation of China(No.91852102)。
文摘The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration.Some results are compared with the experimental data.The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable,and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow.The changes of the particle number concentration M_(0) and the geometric mean diameter dg are more obvious in the core area of the jet,but less obvious in other areas.With the increase in the initial particle number concentration m00,the values of M_(0) and the standard deviation of the particle sizeσdecrease,but the value of d_(g) increases.The decrease in the initial particle diameter leads to the reduction of M_(0) andσand the increase in d_(g).With the increase in the Reynolds number,particles have few chances of collision,and hence the coagulation rate is reduced,leading to the increase in M_(0) andσand the decrease in d_(g).
基金Funding was provided by National Natural Science Foundation of China(Grant No.51761135106)Fundamental Research Funds for the Central Universities,Science Challenge Project(Grant Nos.TZ2018006-0201-02,TZ2018006-0205-02)State Key Lab of Digital Manufacturing Equipment and Technology(Grant Nos.DMETKF 2018007,DMETKF2019016).
文摘Characteristics of internal microstructures have a strong impact on the properties of particulate reinforced metal composites.In the present work,we perform finite element simulations to elucidate fundamental mechanisms involved in the ultraprecision orthogonal cutting of aluminum-based silicon carbide composites(SiCp/AI),with an emphasis on the influence of particle distribution characteristic.The SiCp/AI composite with a particle volume fraction of 25 vol%and a mean particle size of 10|im consists of randomly distributed polygon-shaped SiC particles,the elastic deformation and brittle failure of which are described by the brittle cracking model.Simulation results reveal that in addition to metal matrix tearing,cuttinginduced particle deformation in terms of dislodging,debonding,and cracking plays an important role in the microscopic deformation and correlated machining force variation and machined surface integrity.It is found that the standard deviation of particle size to the mean value has a strong influence on the machinability of microscopic particle-tool edge interactions and macroscopically observed machining results.The present work provides a guideline for the rational synthesis of particulate-reinforced metal composites with high machinability.
基金The National Key Research and Development Program(2020YFA0906804)the National Natural Science Foundation of China(22078325,22035007,91934301)+1 种基金the NSFC-EU project(31961133018)the Special Project of Strategic Leading Science and Technology,CAS(XDC06010302)are gratefully acknowledged.
文摘The particle size distribution of polymer always develops in emulsion polymerization systems,and certain key phenomena/mechanisms as well as properties of the final product are significantly affected by this distribution.This review mainly focuses on the measurement methods of particle size distribution rather than average particle size during the emulsion polymerization process,including the existing off-line,on-line,and in-line measurement methods.Moreover,the principle,resolution,performance,advantages,and drawbacks of various methods for evaluating particle size distribution are contrasted and illustrated.Besides,several possible development directions or solutions of the in-line measurement technology are explored.
基金supported by the National Natural Science Foundation of China (No. 50678047)the National High Technology Research and Development Program of China (No. 2006AA06Z305)the National Science and Technology Project of Eleventh Five Years (No.2006BAJ08B05-2)
文摘Polyaluminum chloride (PAC) was used as coagulant and suspended particles in kaolin water. Online instruments including turbidimeter and particle counter were used to monitor the flocculation process. An evaluation model for demonstrating the impact on the flocculation effect was established based on the multiple linear regression analysis method. The parameter of the index weight of channels quantitatively described how the variation of floc particle population in different size ranges cause the decrement of turbidity. The study showed that the floc particles in different size ranges contributed differently to the decrease of turbidity and that the index weight of channel could excellently indicate the impact degree of floc particles dynamic distribution on flocculation effect. Therefore, the parameter may significantly benefit the development of coagulation and sedimentation techniques as well as the optimal coagulant selection.
基金financially supported by the National Natural Science Foundation of China(Grant No.41790432)Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA20030301)。
文摘Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of this paper is to suggest an appropriate method to assess internal erosion potential of gravelly soil.By analyzing the sensitivity of soil material to internal erosion,the variable(Dc15/df85)max and the content of coarse particles(Pc)are selected as the evaluation indexes(Dc15 and df85 are the diameters of 15%mass passing in the coarse component and 85%mass passing in the fine component,respectively).A series of gravelly soils with different particle size distributions are tested for internal erosion by the self-made permeameter.Based on the test results,an evaluation method for the internal erosion of gravelly soil is proposed.Gravelly soil is prone to internal erosion when 60%≤Pc<95%and(Dc15/df85)max≥9.5.The proposed method shows good accuracy in evaluating the internal erosion of 36 soil samples from other studies,which confirms the reliability of the method.The proposed method makes it possible to accurately assess internal erosion of gravelly soil,and an alternative method is provided for engineers to determine whether there is a risk of internal erosion in earth structures consisting of gravelly soil.
基金supported by the National Natural Science Foundation of China (No: 51806103)Jiangsu Provincial Natural Science Foundation(No: BK20170800)Open Funds of Aero-engine Thermal Environment and Structure Key Laboratory of Ministry of Industry and Information Technology (No. CEPE2018005)
文摘The weighted-sum-of-gray-gas(WSGG)model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures,such as the flame in aero-engine combustor.The radiative transfer equation is solved by the finite volume method.The particle size is assumed to obey uniform distribution and logarithmic normal(L-N)distribution,respectively.Results reveal that when particle size obeys uniform distribution,increasing particle size with total particle volume fraction fvunchanged will result in the decreasing of the absolute value of radiative heat transfer properties,and the effect of ignoring particle scattering will also be weakened.Opposite conclusions can be obtained when total particle number concentration N0 is unchanged.Moreover,if particle size obeys L-N distribution,increasing the narrowness indexσor decreasing the characteristic diameter Dˉwith the total particle volume fraction fvunchanged will increase the absolute value of radiative heat transfer properties.With total particle number concentration N0 unchanged,opposite conclusions for radiative heat source and incident radiation terms can be obtained except for radiative heat flux term.As a whole,the effects of particle size on the radiative heat transfer in the high-temperature homogeneous gas-particle mixtures are complicated,and the particle scattering cannot be ignoring just according to the particle size.
文摘Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities. Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.
基金funded by the National Key R&D Program of China(2017YFD0800505)Chongqing Key R&D Project of Technology Innovation and Application(NO.cstc2018jscxmszd X0055)。
文摘Characterizing soil particle-size distribution is a key measure towards soil property.The purpose of this study was to evaluate the multifractal characteristics of soil particle-size distribution among different land-use from a purple soil catchment and to generalize the spatial variation trend of multifractal parameters across the catchment.A total of 84 soil samples were collected from four kinds of land use patterns(dry land,orchard,paddy,and forest)in an agricultural catchment in the Three Gorges Reservoir Region,China.The multifractal analysis method was applied to quantitatively characterize the soil particle size distribution.Six soil particle size distribution(PSD)multifractal parameters(D(0),D(1),D(2),(35)a(q),(35)f[a(q)],α(0))were computed.Additionally,a geostatistical analysis was employed to reveal the spatial differentiation and map the spatial distribution of these parameters.Evident multifractal characteristics were found.The trend of generalized dimension spectrum of four land use patterns was basically consistent with the range of 0.8 to 2.0.However,orchard showed the largest monotonic decline,while the forest demonstrated the smallest decrease.D(0)of the four land use patterns were ranked as:dry land<orchard<forest<paddy,the order of D(1)was:dry land<paddy<orchard<forest,D(2)presented a rand-size relationship as dry land<forest<paddy<orchard.Furthermore,all land-use patterns presented asΔf[α(q)]<0.The rand-size relationship ofα(0)was same as D(0).The best-fitting model for D(0),D(1),D(2)andΔf[α(q)]was spherical model,forΔα(q)was gaussian model,and forα(0)was exponential model with structure variance ratio was 1.03%,49.83%,0.84%,1.48%,22.20%and 10.60%,respectively.The results showed that soil particles of each land use pattern were distributed unevenly.The multifractal parameters under different land use have significant differences,except forΔα(q).Differences in the composition of soil particles lead to differences in the multifractal properties even though they belong to the same soil texture.Farming behavior may refine particles and enhance the heterogeneity of soil particle distribution.Our results provide an effective reference for quantifying the impact of human activities on soil system in the Three Gorges Reservoir region.
文摘The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stability of the solution obtained from DDF method has been investigated through optimizing the coefficient matrix, introducing a damping factor and a least square treatment. All calculations were accomplished with a microcomputer. It was shown that the average deviations of the size distribution obtained are not larger than the assigned random errors to the scattering intensities as long as the corresponding requirements are satisfied.
文摘An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.
基金financially supported by the National Natural Science Foundation of China(No.51376095)the Jiangsu Province Environmental Research Projects(No.2014049)
文摘Based on the laser diffraction and Shifrin transform,the measurement method of particle size distribution has been improved extensively.While in real measurements,some noise peaks exist in the inversion data and are easily to be misread as particle distribution peaks.The improved method used a truncation function as a filter is hard to distinguish adjacent peaks.Here,by introducing the bimodal resolution criterion,the filter function is optimized,and to a quasi truncation function with the optimized filter function is studied to achieve optimal bimodal resolution and to remove noise peaks.This new quasi truncation function fits multimode distribution very well.By combining the quasi truncation function with Shifrin transform,noise peaks are removed well and the adjacent peaks are distinguished clearly.Finally,laser diffraction experiments are conducted and the particle size distribution is analyzed by adoping the method.The results show that the quasi truncation function has better bimodal resolution than the truncation function.Generally,by combining the quasi truncation function with the Shifrin transform,in particle size distribution measurements with laser diffraction,the bimodal resolution is greatly increased and the noise is removed well.And the results can restore the original distribution perfectly.Therefore,the new method with combination of the quasi truncation function and the Shifrin transform provides a feasible and effective way to measure the multimode particle size distribution by laser diffraction.
文摘This paper deals with the preblem of existence and uniqueness of the stationary distributions (abbr., s. d.'s) for the processes constructed in [4] .The main results are stated in § 1. For the reader's convenience we first restate the existence theorems (Theorem 1 and 2) of the processes given in [4]. Then two existence theorems (Theorem 3 and 4) and a uniqueness theorem (Theorem 5) for the s. d.'s of the processes are presented. The last result (Theorem 6), as an application of the previous ones, is about the Schlgl model which comes from nonequilibrium statisticali physics. The details of the proofs of Theorem 3—6 are given in § 2—4.
文摘The effect of particle size distribution of alumina has been investigated for silica-free tabular alumina low cement castables( LCC). Three different combinations of alumina have been included in the matrix formulation of the castables. All the three combinations are composed of a bimodal reactive alumina and a fine ground monomodal reactive alumina. The first A1 and second A2 combinations are respectively composed of bimodal and monomodal aluminas from Alteo,with a different fine /coarse particles ratio for the bimodal alumina. The two Alteo combinations have been compared with a third combination C composed of a bimodal commercially available grade and a monomodal commercially available grade. Optimization of particle size packing has been performed for the three different formulations using the Dinger and Funk model. With this optimization,the two formulations based on Alteo material( PFR,PBR and PFR40) achieve the same level of performance in applicative tests( flowability,cold physical properties,mechanical resistance,crystalline phases,thermal shocks and corrosion) as reference solutions on the market.
文摘Particle size, textural and surface characteristics influence some major technological properties of high siliceous aluminosilicate zeolite and sillicoaluminophosphate (SAPO) microporous materials. A comparative study was furnished for measuring surface characteristics, particle size and particle size distribution using particle size analyzer (PSA) and scanning electron microscope (SEM). The PSA is capable of measuring particle diameter in micron range. The results of these techniques for estimation of particle size were compared and correlated statistically. Student t-test and variance ratio test (F-test) methods were performed for the significance of results by the analysis of variance (ANONA) and multiple-range tests. Textural and surface characteristics were evaluated by Brunauer, Emmett & Teller (BET) volumetric technique and v-αs plotting method. The textural results shows that the external surface area and micropore volume of microporous materials were higher than those of the high siliceous zeolites and its zeotype materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.41676078,51409088 and41506100)the Natural Science Foundation of Jiangsu Province(Grant No.BK20151499)+1 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.2015B16114,2015B26414 and 2015B34914)the Project of Jiangsu Provincial Six Talent Peaks(Grant No.XXRJ-008)
文摘Particle size distributions (PSDs) of bottom sediments in a coastal zone are generally multimodal due to the complexity of the dynamic environment. In this paper, bottom sediments along the deep channel of the Pearl River Estuary (PRE) are used to understand the multimodal PSDs' characteristics and the corresponding depositional environment. The results of curve-fitting analysis indicate that the near-bottom sediments in the deep channel generally have a bimodal distribution with a fine component and a relatively coarse component. The particle size distribution of bimodal sediment samples can be expressed as the sum of two lognormal functions and the parameters for each component can be determined. At each station of the PRE, the fine component makes up less volume of the sediments and is relatively poorly sorted. The relatively coarse component, which is the major component of the sediments, is even more poorly sorted. The interrelations between the dynamics and particle size of the bottom sediment in the deep channel of the PRE have also been investigated by the field measurement and simulated data. The critical shear velocity and the shear velocity are calculated to study the stability of the deep channel. The results indicate that the critical shear velocity has a similar distribution over large part of the deep channel due to the similar particle size distribution of sediments. Based on a comparison between the critical shear velocities derived from sedimentary parameters and the shear velocities obtained by tidal currents, it is likely that the depositional area is mainly distributed in the northern part of the channel, while the southern part of the deep channel has to face higher erosion risk.