陶瓷膜过滤微米级颗粒悬浮液操作条件的影响

测定不同操作条件下陶瓷膜过滤微米级颗粒悬浮液的渗透能量数据,并与决定膜污染柚是的ｄｐ／ｄｍ的结合进行分析,确定了操作条件对微炫有颗粒悬浮液微滤过程的影响,获得了陶瓷膜微滤微米级颗粒悬浮液过程中操作条件方法。为促进陶瓷膜在涉及微米级颗粒悬浮液分离领域中的应用尊定基础。     

MEASUREMENT OF PARTICLE SIZE DISTRIBUTION IN COAL OIL WATER FUELS BY FOUR METHODS

Four methods were used to measure the solids particle size distribution in coal-ol1-water fuel. Both dry and wet screening were utilized for the coarser particles while four different instrumental methods were used to measure the finer particles in diluted liquid suspension. The wet stages of the analyses included both solvent-diluted organic suspensions and measurement after inversion to an aqueous system.

Consistent differences in the absolute values of particle size were observed between the four procedures. Possible reasons for these differences are discussed.     

Cold compaction of polymeric powders

Using single end compaction in an instrumented cylindrical die, the compaction characteristics of a variety of polymeric powders have been studied. The powders tested range from those which compact very well to those which do not compact at all. Using scanning electron microscopy, the particle size and shape for each powder has been noted and used in conjunction with other physical properties and deformation characteristics to identify the factors which enhance compactability. In general it has been found that a powder with a combination of small particle size, irregular shaped particles and a relatively low bulk modulus is most likely to compact well. As the physical characteristics depart from these desirable conditions the compactability of the powder is reduced.     

Effective thermal conductivity of Cu/diamond composites containing connected particles

An analytical model for the thermal conductivity of Cu/diamond composites with connected particles is presented by replacement of a cluster of connected particles with an equivalent polycrystal subsequently using a multiple effective medium approach. By applying this model to the measured thermal conductivity of Cu/diamond composites prepared by high pressure high temperature sintering technique reported in the literature, we show that it quite well describes the observed thermal conductivity enhancement induced by the connected particles. We estimate the value of connected particle loading in real composites and show that large particles are easier to form the bonding contact than small particles. The present work also demonstrates that the sensitivity of thermal conductivity contribution from the connected particles strongly depends on the particle size, and their pronounced thermal conductivity enhancement should lie within the certain particle size range.     

Tortuosity of porous particles

Tortuosity is often used as an adjustable parameter in models of transfer properties through porous media. This parameter, not reducible to classical measured microstructural parameters like specific surface area, porosity, or pore size distribution, reflects the efficiency of percolation paths, which is linked to the topology of the material. The measurement of the effective conductivity of a bed of particles saturated with an electrolyte is a simple way to evaluate tortuosity. Nevertheless, it received only little attention because of the real difficulties in both getting reliable results and interpreting data. Notably, the discrimination between the contribution of interparticle and intraparticle porosities to the tortuosity is not resolved. To our knowledge, there is no model able to fit the experimental data of the tortuosity of a suspension, and a fortiori of a particle bed, in the whole porosity range. Only empirical expressions have been proposed, but they do not allow deriving intratortuosity of a porous particle. For a dilute system, Maxwell's equation predicts the effective conductivity of suspensions of spherical particles as a function of the bulk electrolyte conductivity and of particle conductivity. The intraparticle tortuosity can be derived from the particle conductivity obtained from the Maxwell equation applied to data at infinite dilution of particles. Then, by assuming that the Maxwell equation is a first-order approximation of the conductivity as a function of porosity, we propose an explicit relation of the tortuosity tau of a suspension of porous particles, obtained by conductivity measurement, as tau = tau(epsilon, epsilon(p), tau(p)), where epsilon is the total porosity of the suspension, tau(p) is the intraparticle tortuosity, and epsilon(p) is the particle porosity. This relationship fits the experimental data in the whole porosity range and can be used to determine tau(p) from an experiment at only one porosity. Finally, the obtained values of tau(p) for a set of porous particles used in chromatography are discussed and compared to the data available in the literature.     

MEASUREMENT OF PARTICLE SIZE DISTRIBUTION IN COAL OIL WATER FUELS BY FOUR METHODS

ABSTRACT

Four methods were used to measure the solids particle size distribution in coal-ol1-water fuel. Both dry and wet screening were utilized for the coarser particles while four different instrumental methods were used to measure the finer particles in diluted liquid suspension. The wet stages of the analyses included both solvent-diluted organic suspensions and measurement after inversion to an aqueous system.

Consistent differences in the absolute values of particle size were observed between the four procedures. Possible reasons for these differences are discussed.     

From Single Particle AFM Studies of Adhesion and Friction to Bulk Flow: Forging the Links

The atomic force microscope (AFM) has been used to study inter-particle contacts in air for a range of model particles and cohesive granular materials of commercial importance. Adhesion (or pull-off force), friction and its load dependence, and particle size, morphology and roughness were measured for glass ballotini, fumed silica, alumina, limestone, titania and zeolite. Particle-wall contacts and effects of relative humidity were also studied. Most of the results, after allowing for roughness, are consistent with JKR contact mechanics and capillary bridge theory; however, the main object of the present work is to demonstrate semi-quantitative links between the AFM measurements and related bulk flow and cohesion measurements performed in parallel on the same materials. A simple model of a particle assembly will be used to compare average contact forces in typical single-particle AFM experiments and typical bulk experiments, and thus identify those regimes of powder flow where the two approaches overlap, and AFM measurements may be used with some confidence in more sophisticated modeling based on distinct element analysis (DEA). Four areas will be discussed briefly: (1) The apparent analogy between bulk yield loci and single-particle friction-load data; (2) Cohesion data and particle size effects; (3) Bulk tensile strength and single particle pull-off force; (4) Bulk wall friction and single-particle-wall friction. It is found that typical single-particle AFM experiments and bulk shear experiments converge for small particles (～ 4 μm) and low consolidation stress, when the average inter-particle contact forces are of the order 20–100nN, involve single or few asperities, and are not much larger than pull-off forces. For large particles and high consolidation loads the data do not overlap and AFM measurements may be less useful as input to simulations where sliding friction is less important, and where large normal contact forces dominate over tangential forces and are responsible for the shear strength.     

Non-Settling Super-Strong Magnetorheological Fluids

A magnetorheological (MR) fluid is generally called a suspension in which magnetic particles are dispersed in a non-magnetic medium. When an external magnetic field is applied, a pseudo-phase transition occurs within a short time to generate yield stress, and when the magnetic field is released, it returns to the suspended state. Due to these unique characteristics, it is classified as a smart material to be widely applied in various industries. High performance MR fluids require high yield stress and stability for long-term use. However, it is very difficult to improve performance and stability simultaneously due to the limited amount of magnetic particles in the suspension and particle sedimentation caused by the density mismatch between the suspending particles and the liquid phase. In this study, an MR slurry is developed that is completely different from the MR suspension, starting from the opposite concept. An innovative non-settling (i.e., permanently stable) magnetorheological slurry is successfully created that exhibits unprecedented ultra-high yield stress. This result is expected to be a turning point for applying MR fluids to more diverse industries. In addition, a simple fitting equation expressing the yield stress as a function of the particle volume fraction is proposed.     

A mixed contact model for an immersed collision between two solid surfaces

Experimental evidence shows that the presence of an ambient liquid can greatly modify the collision process between two solid surfaces. Interactions between the solid surfaces and the surrounding liquid result in energy dissipation at the particle level, which leads to solid-liquid mixture rheology deviating from dry granular flow behaviour. The present work investigates how the surrounding liquid modifies the impact and rebound of solid spheres. Existing collision models use elastohydrodynamic lubrication (EHL) theory to address the surface deformation under the developing lubrication pressure, thereby coupling the motion of the liquid and solid. With EHL theory, idealized smooth particles are made to rebound from a lubrication film. Modified EHL models, however, allow particles to rebound from mutual contacts of surface asperities, assuming negligible liquid effects. In this work, a new contact mechanism, 'mixed contact', is formulated, which considers the interplay between the asperities and the interstitial liquid as part of a hybrid rebound scheme. A recovery factor is further proposed to characterize the additional energy loss due to asperity-liquid interactions. The resulting collision model is evaluated through comparisons with experimental data, exhibiting a better performance than the existing models. In addition to the three non-dimensional numbers that result from the EHL analysis--the wet coefficient of restitution, the particle Stokes number and the elasticity parameter--a fourth parameter is introduced to correlate particle impact momentum to the EHL deformation impulse. This generalized collision model covers a wide range of impact conditions and could be employed in numerical codes to simulate the bulk motion of solid particles with non-negligible liquid effects.     

Experimental investigation of bubble and particle motion behaviors in a gas-solid fluidized bed with side wall liquid spray

Bubble and particle motion behaviors are investigated experimentally in a gas solid fluidized bed with liquid spray on the side wall. The particles used in the experiment are classified as Geldart B particles. The results reveal that when the fluid drag force is less than the liquid bridge force between particles, liquid distribute all over the bed. Bubble size increases as the increase of inter-particle force, then decreases owing to the increase of particle weight with increasing liquid flow rate. When the fluid drag force is greater than the liquid bridge force, liquid mainly distribute in the upper part of the bed. And it is difficult for the wet particles to form agglomerates. Bubble size decreases with increasing liquid flow rate due to the increasing of minimum fluidization velocity. Besides, the acoustic emission (AE) measurements illustrate that the liquid adhesion and evaporation on particles could enhance the particles motion intensity. Consequently, the bubble and particle behaviors change due to the variation in fluidized gas velocity and liquid flow rate should be seriously considered when attempting to successfully design and operate the side wall liquid spray gas solid fluidized bed.     

Influence of the Size of Micronized Active Pharmaceutical Ingredient on the Aerodynamic Particle Size and Stability of a Metered Dose Inhaler

Pharmaceutical inhalers are often used to treat pulmonary diseases. Only active pharmaceutical ingredient (API) particles from these inhalers that are less than approximately 5 µm are likely to reach the lung and be efficacious. This study was designed to investigate the impact of micronized API particle size on the aerodynamic particle size distribution (PSD) profile and the particle size stability of a suspension metered dose inhaler (MDI) containing propellant HFA‐227 (1,1,1,2,3,3,3 heptafluoropropane) and a corticosteroid. The median API particle size ranged from 1.1 µm to 1.8 µm (97% to 70% of particles <?3 µm, respectively). This study showed that increasing the particle size of the API used to manufacture a suspension MDI product increased the aerodynamic PSD of the MDI product. Furthermore, upon storage of the MDI product under temperature cycling conditions, samples containing larger‐size API particles were less stable with respect to their aerodynamic PSD than those with smaller‐size API particles. It was found that size‐dependent particle growth and/or aggregation of the suspended API may be occurring as a result of temperature cycling. In conclusion, this study has shown that the particle size of the raw API impacts the properties and stability of the emitted aerosol spray. Based on the findings from this study, it is recommended that the API particle size be carefully controlled in order to meet specifications set for the finished MDI product.     

Influence of the storage orientation on the aerodynamic particle size of a suspension metered dose inhaler containing propellant HFA-227

Presented in this work are the results of a study designed to investigate the impact of the storage position on the particle size distribution (PSD) of a steroid suspension metered dose inhaler (MDI) containing propellant HFA-227. It was hypothesized that the orientation of MDI samples upon storage could influence the PSD of the emitted dose, since it determines the amount of contact the liquid formulation has with the valve and therefore the quantity of nonvolatile leachable materials from the valve components that may enter the product and potentially impact the aerosol spray dynamics. Samples stored in the valve down orientation (i.e., complete contact of the liquid formulation with the valve) showed a higher level of leachables compared to those samples stored valve up (i.e., minimal contact of the formulation with the valve). The valve down samples were found to produce larger particles in the emitted aerosol spray using both cascade impaction, the preferred method of regulatory submission, as well as laser diffraction. It was postulated that the larger particle size of the inverted samples was attributed to its higher levels of leachables. Based on our findings, it is recommended that in order to set appropriate controls on the product PSD, the storage orientation of the product will need to be considered.     

A NUMERICAL MODEL FOR STEADY NONPOINT SOURCE DISPERSION OF WIND-BLOWN FINE PARTICLES FROM STORAGE PILES AND EXPERIMENTAL STUDY

This study is concerned with modeling of the loss of fine dust from storage piles and their dispersion in the atmosphere. The results of downwind particulate dispersion are tested by means of a two-dimensional wind tunnel model using tracer particles. The study shows that a wind barrier located two to three pile heights upstream will effectively reduce the wind blowing of fine particles from storage piles and the downwind particle density. The tracers used in the experiment are smoke, magnesia, latex, and glass particles. The particle sizes studied range from 15 μm to 75 μm. Experimental results indicate that the effects of particle settling due to gravity force will be negligible when the particle settling velocity is less than 0.03 m/s. If particle size is less than 15 μm, particles will most likely remain in a suspension state over a long distance. Finite difference techniques are used for steady state numerical simulation of particulate dispersion. The effects of the particle sizes, wind velocity, and the ground conditions on the downwind particle density distribution are presented.     

A microscopic model for predicting hot-spot ignition of granular energetic crystals in response to drop-weight impacts

A micro-mechanics model describing hot-spot formation in the energetic crystal powders cyclotetramethylene tetranitramine (HMX) and pentaerythritol tetranitrate (PETN) subjected to drop-weight impact is developed. Considering contact deformation, friction and chemical reactions at the particle level during the impact loading process, three hot-spot sources are included, namely, the micro-particle contact deformation between two equal-sized particles with no relative sliding, the contact sites between the impacting surface and the particles, and the contacting zone between particles with a sliding velocity along the maximum shear-stress direction. Drop-weight impacts on samples composed of equal-sized particle layers are considered. The temperature rise due to plastic and frictional dissipation is estimated, and melting is included. Hot spot ignition is predicted via thermal explosion, using an Arrhenius thermochemical model. The effects of drop height and particle size on the ignition processes are analyzed. The hot-spot sources at the interface between the particles and the impacting surfaces play the most important role during the early ignition stage. The time-to-ignition of the three sources increases with decreasing drop height. Calculated results show that the HMX and PETN crystals demonstrate monotonously increasing time-to-ignition with a reduction in particle size. The effect of particlesize on the hot spot ignition threshold can be predicted. Samples with a smaller particle size undergo larger localized deformations and lower average pressures.     

Using a coupled CFD – DPM approach to predict particle settling in a horizontal air stream

Preventing health and safety hazards such as dust explosions and respiratory exposure in the work force when handling and storing fine powders is a major challenge faced by plant operators [13]. Computational Fluid Dynamics (CFD) coupled with Discrete Phase Model (DPM) can be used as a tool to address this challenge by advancing the understanding of how particles deposit in a particular process. Particle settling, in air streams, is primarily dependent on the drag forces exerted on the individual particles through interactions with the suspension medium [2]. By improving the understanding of this interaction through repeatable experiments and simulations; more complex CFD – DPM simulations are possible, thus providing a significant step in reducing the risks associated with handling fine powders. To study the transport and settling of particles in air streams, an experiment was established where glass beads, alumina and iron ore dust were injected into a horizontal flow channel. The material was fed into the top of the test rig where it was then transported in a laminar air stream. Through this method particle settling, according to the particle size, can be observed by sampling different trays along the bottom of the test rig. Once the deposition of particles is analysed (using a particle size analyser) each diameter range can be tracked to determine the distance travelled. After evaluating these experiments a CFD coupled with DPM simulation was employed to predict particle deposition in the horizontal chamber. The results show a good agreement between experiments and CFD – DPM results.     

Numerical simulation of sedimentation in the presence of 2D compressible convection and reconstruction of the particle-radius distribution function

Numerical simulation of the sedimentation of a polydisperse suspension in a convectively unstable medium is presented. For the simulation of 2D compressible convection, the full system of hydrodynamic equations is solved by the explicit MacCormack scheme. Velocities and positions of suspension particles are calculated simultaneously with the solution of the equations. Initially, the particles are randomly distributed in the computational region. The total weight of sedimented matter is recorded during the numerical experiment. The results are compared with the sedimentation of the same suspension without convection. To reconstruct the particle-radius distribution function from the sedimentation curve, a new method is used. This method is based on the solution of the sedimentation integral equation by the Tikhonov regularization method and was recently developed by the author. To illustrate this technique, sedimentation of cement powder in air is simulated. The suspension contains 50000 particles. The particle radii are assumed to be log-normally distributed. Heat-driven convection is completely determined by the top and bottom boundary temperatures of the computational region and lateral boundary conditions. It is shown that convective motions of a medium with sedimented particles lead to the following effect: the fine disperse fraction of the suspension remains suspended much longer than without convection. Some particles will not sediment at all. The maximum radius of the particles of this fraction depends on the convection parameters (e.g. on convection cell size and convection velocities). These parameters, in their turn, depend only on the temperature difference of the top and bottom boundaries. The results of these calculations can be applied in geology and meteorology for studying dust sedimentation in air as well as in technology. Heat-driven convection can be used for separation of suspensions with the cut-off particle radius depending on temperature difference only.     

High-precision sizing of nanoparticles by laser transmission spectroscopy

We describe the implementation of precision laser transmission spectroscopy for sizing and counting nanoparticles in suspension. Our apparatus incorporates a tunable laser and balanced optical system that measures light transmission over a wide (210-2300 nm) wavelength range with high precision and sensitivity. Spectral inversion is employed to determine both the particle size distribution and absolute particle density. In this paper we discuss results for particles with sizes (diameters) in the range from 5 to 3000 nm. For polystyrene particles 404 to 1025 nm in size, uncertainties of ±0.5% in size and ±4% in density were obtained. For polystyrene particles from 46 to 3000 nm in size, the dynamic range of the system spans densities from ~10(3)/ml to ~10(10)/ml (5 × 10(-8) to 0.5 vol. %), implying a sensitivity 5 orders of magnitude higher than dynamic light scattering.     

PARTICLE COUNTING OIL AND WATER EMULSIONS

Because of their speed and convenience, optical particle counters are widely used for particle size analysis of liquid samples. In some cases, both solid particles and emulsified water or oil may be present in a sample. Since emulsion droplets are counted as if they are solid particles, analysis and data interpretation for these samples are difficult. Until recently, no suitable method existed for distinguishing solid contaminants from emulsion droplets. This paper discusses a method which overcomes this limitation. Through the use of a surfactant-laden nonpolar dilution fluid, water is incorporated into reverse micelles too small to be seen by most optical particle counters. As a result, only solid contaminants are counted, and many problems associated with the analysis of emulsions are overcome. Results obtained from a wide range of oil and water emulsions are used to evaluate the merits and possible applications of the new technique.     

Modelling of filtration processes of fibrous filter media

This work presents a stochastic approach, based on Monte Carlo method, to simulate liquid filtration processes through non-woven fibrous materials. The real filter material is represented as a multilayer medium with a network of multiply connected pores. To describe the deposition and resuspension of particles on and from the filter medium, the following four mechanisms were considered: particle capture by sieving, patricle capture by fibers; particle capture by blocked pores; and particle re-entrainment. The particle capture by fibers and blocked pores, and particle re-entrainment depend on the balance between the adhesion and removal forces. The adhesion forces for particles of diameter smaller than 20 μm were determined through the concept of London-Van Der Waals forces. For particles of diameter greater than 20 μm, gravitational forces were considered. Three-dimensional random flow was assumed to stimulate the particles motion through the multilayer medium. The pressure drop across the filter medium was calculated as the sum of the pressure drop across the clean filter plus the pressure drop due to the deposited particles.A FORTRAN Program was developed to implement the filtration process model. For a wide range of typical filtration conditions, the calculated filter efficiencies predicted the experimental results with a percent difference between 0.5 and 19.3 depending on the particle size. The filter material capacities were predicted with an average discrepancy of 23.0%