A Typical Production and Elimination Process of Particles in Beijing during Early 2008 Olympic Games

[Objective] The aim was to discuss he produce and elimination rules of particles in Beijing during early 2008 Olympic Games. [Method] Based on the analysis of particulate matter online observation data and meteorological data during the corresponding period in Chinese environmental science college, Hysplit Back trace model and Numerical weather prediction graphs, and combined with the different analytical methods on meteorological flow fields, a typical process of particles in Beijing during early 2008 Olympic Games was studied. [Result] The results indicated that during the ascent stage of PM2.5 concentration, the PM showed gradually aging phenomena; the process controlled by large scale synoptic system mainly. And the weak wind and the high humidity were not in favor of dispersion; the prolonged southerly air mass to bring the pollutant of Hebei, Taijin and Shandong to Beijing; mixing height and temperature curve took the importance role to the pollution. [Conclusion] The study provided theoretical basis for the discussion on factors influencing the production and elimination of particles in the air pollution process.

Magnetization Reversal Process of Single Crystal a-Fe Containing a Nonmagnetic Particle

The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.

Influence of vibration mode on the screening process

The screening of particles with different vibration modes was simulated by means of a 3D discrete element method (3D-DEM). The motion and penetration of the particles on the screen deck were analyzed for linear, circular and elliptical vibration of the screen. The results show that the travel velocity of the particles is the fastest, but the screening efficiency is the lowest, for the linear vibration mode. The circular motion resulted in the highest screening efficiency, but the lowest particle travel velocity. In the steady state the screening efficiency for each mode is seen to increase gradually along the longitudinal direction of the deck. The screening efficiency increment of the circular mode is the largest while the linear mode shows the smallest increment. The volume fraction of near-mesh size particles at the underside is larger than that of small size particles all along the screen deck. Linear screening mode has more near-mesh and small size particles on the first three deck sections, and fewer on the last two sections, compared to the circular or elliptical modes.

An improved particle tracking velocimetry(PTV) technique to evaluate the velocity field of saltating particles

Velocity is a key parameter characterizing the movement of saltating particles. High-speed photography is an efficient method to record the velocity. But, manually determining the relevant information from these photographs is quite laborious. However, particle tracking velocimetry（PTV） can be used to measure the instantaneous velocity in fluids using tracer particles. The tracer particles have three basic features in fluids： similar movement patterns within a small region, a uniform particle distribution, and high particle density. Unfortunately, the saltation of sand particles in air is a stochastic process, and PTV has not yet been able to accurately determine the velocity field in a cloud of blowing sand. The aim of the present study was to develop an improved PTV technique to measure the downwind（horizontal） and vertical velocities of saltating sand. To demonstrate the feasibility of this new technique, we used it to investigate two-dimensional saltation of particles above a loose sand surface in a wind tunnel. We analyzed the properties of the saltating particles, including the probability distribution of particle velocity, variations in the mean velocity as a function of height, and particle turbulence. By automating much of the analysis, the improved PTV method can satisfy the requirement for a large sample size and can measure the velocity field of blowing sand more accurately than previously-used techniques. The results shed new light on the complicated mechanisms involved in sand saltation.

Study on the physical basis of pressure and particle velocity combine processing

Some basic studies of pressure and particle velocity combine processing such as correlation between them, average acoustic intensity processing, rotating and sharpening of directivity are described. Preliminary results based on theoretical analysis and lake trail will lay a foundation for further research.

THE MICROPHYSICAL STRUCTURE OF SNOW CLOUDS AND THE GROWTH PROCESS OF SNOW PARTICLES IN WINTER IN XINJIANG

The microphysical structure of snow clouds and the growth process of snow crystals were observed by means of instrumented aircraft, weather radar, snow crystal observations etc. in Urumqi region during the winter of 1982. The analysis of three cases show that about 70% of snow mass growth is produced in the lower layer below 2000 m under the cold front, and that the concentration of ice crystals is as high as 60 L^(-1) and the supercooled water is absent in lower clouds. We may infer that the deposition of ice crystals and the aggregation of snow crystals are important processes for the snow development. The microphysical structure of the snow band near the front aloft and its characteristics as a seeder cloud are also described in this paper.

A combined signal processing approach against coherent interference with pressure and particle velocity

Comparing with traditional underwater acoustic system which only utilizes pressure information, combine sensor system processes pressure together with particle velocity information of sound field. More information certainly brings nicer processing result. By using spatial directional information collected by combine sensor, the Coherent Interference Energy Suppress (CIES) technology, which can effectively suppress coherent interference and detect linear spectrum signal and wide-band continuous-spectrum signal as well, is presented. Current research has shown favorite result, and further research is going on.

VERIFICATION OF SMOM AND QMOM POPULATION BALANCE MODELING IN CFD CODE USING ANALYTICAL SOLUTIONS FOR BATCH PARTICULATE PROCESSES

For many processes of industrial significance, due to the strong coupling between particle interactions and fluid dynamics, the population balance must be solved as part of a computational fluid dynamics （CFD） simulation. In this work, a CFD based population balance model is tested using a batch crystallization reactor. In this CFD model, the population balance is solved by the standard method of moments （SMOM） and the quadrature method of moments （QMOM）. The results of these simulations are compared to analytical solutions for the population balance in a batch tank where 1） nucleation, 2） growth, 3） aggregation, and 4） breakage are taking place separately. The results of these comparisons show that the first 6 moments of the population balance are accurately predicted for nucleation, growth, aggregation and breakage at all times.

In-line imaging measurements of particle size,velocity and concentration in a particulate two-phase flow

A novel method is developed for in-line measurements of particle size, velocity and concentration in a dilute, particulate two-phase flow based on trajectory image processing. The measurement system consists of a common industrial CCD camera, an inexpensive LED light and a telecentric lens. In this work, the image pre-processing steps include stitching, illumination correction, binarization, denoising, and the elimination of unreal and defocused particles. A top-hat transformation is found to be very effective for the binarization of images with non-uniform background illumination. Particle trajectories measured within a certain exposure time are used to directly obtain particle size and velocity. The particle concentration is calculated by using the statistics of recognized particles within the field of view. We validate our method by analyzing experiments in a gas-droplet cyclone separator. This in-line image processing method can significantly reduce the measurement cost and avoid the data inversion process involved in the light scattering method.

Comparison of the standard Euler-Euler and hybrid Euler-Lagrange approaches for modeling particle transport in a pilot-scale circulating fluidized bed

Particle transport phenomena in small-scale circulating fiuidized beds （CFB） can be simulated using the Euler-Euler, discrete element method, and Euler-Lagrange approaches. In this work, a hybrid Euler-Lagrange model known as the dense discrete phase model （DDPM）, which has common roots with the multiphase particle-in-cell model, was applied in simulating particle transport within a mid-sized experimental CFB facility. Implementation of the DDPM into the commercial ANSYS Fluent CFD package is relatively young in comparison with the granular Eulerian model. For that reason, validation of the DDPM approach against experimental data is still required and is addressed in this paper. Additional difficulties encountered in modeling fluidization processes are connected with long calculation times. To reduce times, the complete boiler models are simplified to include just the combustion chamber. Such simplifications introduce errors in the predicted solid distribution in the boiler. To investigate the conse- quences of model reduction, simulations were made using the simplified and complete pilot geometries and compared with experimental data. All simulations were performed using the ANSYSFLUENT 14.0 package. A set of user defined functions were used in the hybrid DDPM and Euler-Euler approaches to recirculate solid particles.

Landmarks in the application of electrical tomography in particle science and technology

Selected milestones in the development and use of electrical tomography in powder conveying, slurry processing and multi-phase flow are highlighted. The ability to map concentration in opaque mixtures under process-realistic conditions was a major innovation for the method and has had far reaching implications. Subsequent developments have enabled velocity information to be abstracted resulting in the ability to measure component flux and motion.

Orderly decorated nanostructural photoelectrodes with uniform spherical TiO2 particles for dye-sensitized solar cells

This study presents a novel nanostructural electrode made of 20-nm-diameter nanoparticles, which orderly decorated with 2-μm TiO2 particles, deposited by a new gel process. The decorated electrode （DE） is better than the non-decorated electrode （NE） in both light scattering and light harvesting, as confirmed by diffuse reflectance spectroscopy. X-ray diffraction reveals that both electrodes have a mixture of anatase and rutile phases. The dye-sensitized solar cell based on the decorated electrode shows the highest power conversion efficiency of 7.80% as a result of less recombination demonstrated by electrochemical impedance spectroscopy. From internal power conversion efficiency measurement, the external quantum efficiency of DE cell at 530 nm is 89%, which is higher than that of NE cell （77%）.

Hydrothermal synthesis of triangular CeCO3OH particles and photoluminescence properties

Ru/CeO_2[RC] and Ru/CeO_2/ethylene glycol（EG） [RCE] nanoparticles were produced by performing a simple hydrothermal reaction at 200℃ for 24 h and found to have two distinct morphologies. The RC nanoparticles are phase pureCeO_2; triangular highly crystallineCeCO_3OH nanoparticles are formed from the solution containing EG under the same hydrothermal reaction conditions at p H 8.5. EG plays an important role in the formation of the triangularCeCO_3OH nanoparticles. The polycrystallineCeCO_3OH nanoparticles retain their triangular structure even after calcination at 600℃in air but are transformed into a pureCeO_2 phase. The room temperature photoluminescence of the RC and RCE nanoparticles and of RCE calcined at 600℃[RCE-600] was also investigated. It was found that the high crystallinity triangular RCE-600 sample exhibits the highest photoluminescence intensity.

A model for expansion ratio in liquid-solid fluidized beds

Liquid-solid fluidized beds are used in mineral processing industries to separate particles based on parti- cle size, density, and shape. Understanding the expanded fluidized bed is vital for accurately assessing its performance. Expansion characteristics of the fluidized bed were studied by performing several experi- ments with iron ore, chromite, quartz, and coal samples. Using water as liquid medium, experiments were conducted to study the effects of particle size, particle density, and superficial velocity on fluidized bed expansion. The experimental data were utilized to develop an empirical mathematical model based on dimensional analysis to estimate the expansion ratio of the fluidized bed in terms of particle character- istics, operating and design parameters. The predicted expansion ratio obtained from the mathematical model is in good agreement with the experimental data.

Polymeric hollow fiber membrane for cooling crystallization seeding:On the mechanism of induced nucleation based on thermal transfer Author links open overlay panel

Cooling crystallization is an important separation process and particuology technology that requires accurate nucleation control strategies.Herein,we introduced the polymeric hollow fiber membrane with proper thermal properties as the effective nucleation induction interface during cooling crystallization.The heterogeneous nucleation control mechanism was introduced based on classical nucleation theory and the thermal transfer process.Interfacial properties and the thermal conductivity of two kinds of polymeric membranes,polytetrafluoroethylene(PTFE)and polyethersulfone(PES),were measured and simulated with the developed model.These two membranes possessed different nucleation induction periods,nucleation rates and crystallization performances,which validated that the hollow fiber membrane module could effectively accelerate the nucleation process compared to conventional cooling crystallization owing to the shorter nucleation induction period and the reduced solution surface tension.Due to the higher hydrophobicity and the lower roughness of the membrane surface,the PTFE membrane possessed a more moderate performance in generating stable heterogeneous nucleation than the one of PES membrane.Thus,the adjustable membrane property enabled the hollow fiber membrane-assisted cooling crystallization to possess the accurate nucleation control and desired terminal particle products.