Decreasing Particle Diameter Research Articles

Research on Characteristic Parameters of Coal-dust Explosion

The parameters of explosive characteristics of the coal-dust are assessed systematically with the test device of minimum ignition temperature of dust clouds and 20L sphere explosion test units. The minimum ignition temperature of dust is a main safety index when handling combustible dusts in industrial production, and while hazard evaluation, the maximum explosion pressure and the explosion index are key parameters. Five kinds of coal-dust with different particle diameters were tested in order to determine the temperature sensitivity and the ferocity under the given conditions, which can be used as the criteria to classify dust explosion hazards. The experiment results indicate that the minimum ignition temperature of coal-dust cloud reduces with the decrease of particle diameter under temperature of (293±5) K and powder spraying pressure of 0.08MPa, and when the particle size reduces to (25-48) μm, the minimum ignition temperature is between (793-803)K; Besides that, the results can also show that minimum explosive concentration of coal-dust cloud is between 20 gam-3 and 30 gam-3under temperature of (293±5) K, powder spraying pressure of 2MPa and ignition energy of 10kJ, the maximum explosion pressure is 0.45MPa and the maximum explosion index is 11.14 MPaamas-1, which classifies coal-dust explosion hazards to Level I. The conclusions drawn from the experimental results are of great significance to the safe application of these combustible substances.

Performance Analysis of a Packed Bed Waste Heat Recovery System Based on Modelling Results

The performance of a cylindrical packed bed waste heat recovery system was analyzed using different mathematical models. The models were compared in terms of accuracy, precision and computational cost. Then, the best model was used to calculate the heat recovery yield and the thermal efficiency of system. The results show that the yield of heat recovery for packed bed increases when the diameter of the particles and the temperature of the inlet gas decreases. Moreover, by increasing the velocity of the inlet gas and time of heating period the yield of the system increases. The efficiency of apparatus increases by decreasing particle diameter, decreasing inlet gas velocity and increasing the inlet gas temperature.

Surfactant adsorption and aggregate structure at silica nanoparticles: Effects of particle size and surface modification

The influence of particle size and a surface modifier on the self-assembly of the nonionic surfactant C12E5 at silica nanoparticles was studied by adsorption measurements and small-angle neutron scattering (SANS). Silica nanoparticles of diameter 13 to 43 nm were synthesized involving the basic amino acid lysine. A strong decrease of the limiting adsorption of C12E5 with decreasing particle diameter was found. To unveil the role of lysine as a surface modifier for the observed size dependence of surfactant adsorption, the morphology of the surfactant aggregates assembled on pure siliceous nanoparticles (Ludox-TMA, 27 nm) and their evolution with increasing lysine concentration at a fixed surfactant-to-silica ratio was studied by SANS. In the absence of lysine, the surfactant forms surface micelles at silica particles. As the concentration of lysine is increased, a gradual transition from the surface micelles to detached wormlike micelles in the bulk solution is observed. The changes in surfactant aggregate morphology cause pronounced changes of the system properties, as is demonstrated by turbidity measurements as a function of temperature. These findings are discussed in terms of particle surface curvature and surfactant binding strength, which present new insight into the delicate balance between the two properties.

G060015 減圧沸騰噴霧による火炎内ナノ粒子合成法の構築

Flame synthesis method is commercially important because of its relative low cost, one-step process and it can be operated as continuous processes. However, a novel flame synthesis method for nanoparticles is proposed to solve several kinds of problem with vapor-to-particles and droplet-to-particles formation processes. For improving their problems, the new nanoparticle synthesis method by applying the flash boiling spray to flame synthesis method is proposed in this study. This method is expected that a uniform particle size, composition and non-agglomerated nanoparticles can be generated in high purity. In the construction of this method, it is important to control the particle nucleation and growth. The particle residence time is a significant process parameter affecting the particle nucleationand growth. Then, it is thought that ambient pressure change the particle residence time. The objective of this report was to investigate the influence of ambient pressure on the TiO_2 particle characteristic. In consequence, as the ambient pressure decrease, the primary particle diameter decrease because of the short particle residence time. And the agglomeration is inhibited by elongating mean free path due to the pressure drop. Moreover, since particle growth was carried out quickly by getting higher ambient pressure, the transformation of anatase to rutile phase was inhibited, and anatase content of product particles synthesized in higher ambient pressure was increased.

H2 splitting on Pt, Ru and Rh nanoparticles supported on sputtered HOPG

The equilibrium hydrogen exchange rate between adsorbed and gas phase hydrogen at 1bar is measured for Pt, Ru and Rh nanoparticles supported on a sputtered HOPG substrate. The particles are prepared by Electron Beam Physical Vapor Deposition and the diameter of the particles varies between 2 and 5nm. The rate of hydrogen exchange is measured in the temperature range 40–200°C at 1bar, by utilization of the H–D exchange reaction. We find that the rate of hydrogen exchange increases with the particle diameter for all the metals, and that the rate for Ru and Rh is higher than for Pt. In the case of Pt, the equilibrium dissociative sticking probability, S, is found to be nearly independent of particle diameter. For Ru and Rh, S is found to depend strongly on particle diameter, with the larger particles being more active. The apparent energy of desorption at equilibrium, Eapp, shows a dramatic increase with decreasing particle diameter for diameters below 5nm for Ru and Rh, whereas Eapp is only weakly dependent on particle diameter for Pt. We suggest that the strong variation in the apparent desorption energy with particle diameter for Ru and Rh is due to the formation of compressed hydrogen adlayers on the terraces of the larger particles. Experiments are also carried out in the presence of 10ppm CO. Pt is found to be very sensitive to CO poisoning and the H–D exchange rate drops below the detection limit when CO is added to the gas mixture. In the case of Ru and Rh nanoparticles, CO decreases the splitting rate significantly, also at 200°C. The variation of the sensitivity to CO poisoning with particle diameter for Ru and Rh is found to be weak.

전기집진기의 10 nm 급 초미세 나노입자의 하전 및 집진 특성

전기집진에서의 10 nm 급 초미세 나노입자의 하전 및 집진 특성을 파악하였고, 나노입자의 확산효과와 비교해 보았다. 나노입자의 하전율과 확산손실 효과의 지배력에 따라 전기집진기에서의 나노입자 집진효율이 결정되는 것을 확인할 수 있었다. 10nm 급 영역에서는 입자 크기가 작아질수록 지속적으로 집진효율이 감소하였다. 10 nm 이하의 영역에서는 나노입자의 부분적 하전효과가 전기집진기 내의 확산손실 효과보다 지배적인 것을 알 수 있었다. 10 nm 이하의 나노입자에 대하여 집진효율 실험 결과가 단극 확산 하전 이론을 적용한 입자하전율 계산 결과와도 잘 일치하였다.

A Numerical Simulation of Diffusion Charging Effect on Collection Efficiency in Wire-Plate Electrostatic Precipitators

In this paper, a numerical simulation was carried out to analyze the effect of diffusion charging on collection efficiency of a wire-plate electrostatic precipitator (ESP). The gas flow field, the electric field, and the particle field with diffusion charging considered were included in the numerical model, which was implemented by using the commercial FLUENT software. Collection efficiency was calculated by using the Deutsch-Anderson equation, in which the parameters were provided from the numerical solutions. The simulated results indicate that the effect of diffusion charging on the wire-plate ESP particle collection increases with the decreasing particle diameter, as well as applied potential, particularly for PM10. Moreover, with the increasing applied potential, collection efficiency of PM10 is obviously improved, and the effect extent first increases and then decreases with particle size increasing, but also, the size range of particle, which is significantly affected by the diffusion charging, becomes smaller. As gas velocity becomes higher, the effect of diffusion charging on grade efficiency also becomes more obvious, and the affected range of particle size gets much larger, however, at the price of grade efficiency decreasing. Using collection efficiency as reference variable of judgment, instead of particle charge, may lead to a more accurate estimation of the aforementioned size range, which can provide a great help in the further analysis of fine particle collection.

Protein UTLC-MALDI–MS using thin films of submicrometer silica particles

Slides for ultra thin-layer chromatography (UTLC) were made by coating nonporous silica particles, chemically modified with polyacrylamide, as 15 μm films on glass or silicon. Three proteins, myoglobin, cytochrome c and lysozyme, are nearly baseline resolved by the mechanism of hydrophilic interaction chromatography. A plate height as low as 3 μm, with 3900 plates, is observed in 14 mm. Varying silica particle diameter among 900, 700 and 350 nm showed that decreasing particle diameter slightly improves resolution but slows the separation. Matrix-assisted laser desorption/ionization (MALDI)-MS of the proteins after separation is demonstrated by wicking sufficient sinapinic acid into the separation medium.

Solid electrolyte films in controlling their structures by electrophoretic deposition method

Improvement of proton conductivity of solid electrolyte films needs to form three-dimensional proton conduction paths by controlling the pore size and the pore structure between particles in particle films. A particle assemble method using electrophoretic deposition technique is useful for speedy and mass production assembly. In the electrophoretic deposition method, structure of particle array can be controlled by the electric field. As a result, the proton conductivity of the film showed a higher value for the regularly-arranged particle film and it is increased with a decrease in particle diameter. The proton conductivity of the film with the particles of diameter 50 nm had the highest value. The particle film with the well-controlled structure may enable the fuel cell to be operated in the middle temperature range.

Biomass Pyrolysis and Gasification of Varying Particle Sizes in a Fluidized-Bed Reactor

A new 4 in. (102 mm) diameter fluidized-bed reactor has been built and used to study the effect of biomass particle size on the yield of light gas and tar compounds during gasification. Batch experiments were conducted with white oak milled into four sphere sizes with diameters of 6, 13, 18, and 25 mm, at reactor bed temperatures of 500, 600, 700, 800, and 900 °C. As expected, the yields of light gas increase with temperature but then reach a plateau above 800 °C. As the particle size increases, a decrease in the formation of light gases, accompanied by an increase in the formation of char, is observed. For larger particle sizes, the commonly used power law dependence of particle devolatilization time with sphere diameter holds true and the transition from heat- and mass-transport control to kinetic control as particle diameter decreases is illustrated. Measurements of the organic compounds present in the syngas are performed using a molecular beam mass spectrometer (MBMS). These measurements indicate tha...

Screening of a Model for the Distribution of Dye in Dye-Encapsulated Silica Through the Gradual Etching of the Outermost Silica Layer Using Hydrofluoric Acid

Monodispersed spherical silica particles emitting blue light were prepared by incorporating 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene (BBOT) into a silica matrix. The morphological and photoluminescent properties were investigated to confirm the proper incorporation of BBOT into the silica matrix, using an electron microscope and a fluorescence spectrometer. Four possible models representing the distribution of the dye molecules in a dye-encapsulated silica particle were proposed. To analyze the distribution of the BBOT dye in the BBOT-encapsulated silica, the fluorescent emission intensity was measured while reducing the particle diameter by etching the outermost silica layer with hydrofluoric acid with 0-0.5 wt.% concentrations. The distribution of BBOT in a silica particle was investigated based on the relationship between the changes in particle diameter and the changes in emission intensity. The emission intensity of the BBOT-encapsulated silica particle oscillated with the decreasing particle diameter. This result supported the multilayered model. Information regarding the distribution of the dye in the silica matrix will provide valuable information for understanding the formation mechanism of dye-encapsulated silica.

Nanoparticle distribution in a rotating curved pipe considering coagulation and dispersion

We study the evolution of the particle number concentration, mass concentration, particle polydispersity, particle diameter and geometric standard deviation considering particle coagulation and dispersion in a rotating curved pipe at different Reynolds number, Schmidt number and F number. It is found that, when the Coriolis force and the centrifugal force point to the same direction, particles concentrate near the outside edge of the pipe, which becomes more obvious as time goes by. The particle number and mass concentration increase faster at the early stage than that at the later stage, and approach a stable value finally. As the coagulation proceeds, the particle diameter, polydispersity and geometric standard deviation increase and have high values in the region close to the outside edge of the pipe. When the Coriolis force and the centrifugal force point to the opposite direction and the Coriolis force is more dominant than the centrifugal force, particles concentrate near the inside edge of the pipe. The particles in the region with a high number concentration have high mass concentration, large diameter and high polydispersity as well as large geometric standard deviation. The particle distribution is dependent on the balance of the pipe curvature and rotating speed. The Reynolds number and the Schmidt number have effects on the particle distribution when other parameters remain unchanged. An increase in the Reynolds number leads to an increase in particle number concentration and mass concentration, and a decrease in particle polydispersity, particle diameter and geometric standard deviation. With the increase of Schmidt number the particle number concentration and mass concentration increase, and the particle polydispersity, particle diameter and geometric standard deviation decrease.

The Investigation of Back-Mixing Particles near Dust Outlet in Cyclone Separator with Tangential Inlet

Based on experimental and computational fluid dynamics analysis, the phenomenon of particle back-mixing near the dust outlet in cyclone separator with tangential inlet was studied. The results show that particle back-mixing appears near the dust outlet geometry. Particle back-mixing can be divided into dust hopper back-mixing and discharge cone back-mixing for different generation mechanism. The upward flow coming from dust hopper, which occupies 17.7% of the inlet gas, can induce dust hopper back-mixing. The particle mass flow rate that caused by dust hopper back-mixing occupies 46.6% of total inlet particle mass flow rate. Precessing vortex core, bias flow and high turbulent intensity near the dust outlet can induce discharge cone back-mixing. For both dust hopper back-mixing and discharge cone back-mixing, particle back-mixing is serious near the dust outlet geometry, which occupies 56.8% of total inlet particle mass flow rate. Particle which is smaller than 18μm can mix backward. The axial distribution of particle concentration decreases sharply in a range of 1.5 D (cyclone diameter) height above the dust discharge port. At last, only 2.6% of back-mixing particles with diameter no bigger than 13μm escape from vortex finder. This effect on separator efficiency increases with the particle diameter decreases.

Study of Platinum Deposition on Untreated and Thermally Modified Glassy Carbon

Platinum was deposited from aqueous sulphuric acid solution of hexachloroplatinic acid under potentiostatic conditions upon untreated as well as thermally treated glassy carbon (GC). The influence of thermal treatment of GC on electrochemical platinum deposition was thoroughly investigated in terms of the size, the size distribution and coverage of Pt deposits, using scanning electron microscopy and X-ray photoelectron spectroscopy. A decrease in Pt particle diameter and an increased Pt coverage was observed for various deposition pulse lengths on thermally pre-treated GC. This thermal pre-treatment led to a formation of a microporous layer on the substrate surface, thus influencing particle size distribution and coverage. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements have shown that the chemical composition and surface roughness of GC are not affected by the treatment.

Influence of processing time on nanoparticle generation during picosecond-pulsed fundamental and second harmonic laser ablation of metals in tetrahydrofuran

The influence of fundamental and second harmonic wavelength on ablation efficiency and nanoparticle properties is studied during picosecond laser ablation of silver, zinc, and magnesium in polymer-doped tetrahydrofuran. Laser ablation in stationary liquid involves simultaneously the fabrication of nanoparticles by ablation of the target material and fragmentation of dispersed nanoparticles by post irradiation. The ratio in which the laser pulse energy contributes to these processes depends on laser wavelength and colloidal properties. For plasmon absorbers (silver), using the second harmonic wavelength leads to a decrease of the nanoparticle productivity over process time along with exponential decrease in particle diameter, while using the fundamental wavelength results in a constant ablation rate and linear decrease in particle diameter. For colloids made of materials without plasmon absorption (zinc, magnesium), laser scattering is the colloidal property that limits nanoparticle productivity by Mie-scattering of dispersed nanoparticle clusters.

Heat Transfer to Flat Strips Immersed in a Fluidized Bed

Heat transfer to objects immersed in a fluidized bed has been studied extensively across a relatively large range of geometries, though most work has looked at cylinders, a geometry important in power generation fluidized bed applications. As the power generation industry has been the primary stimulant to fluidized bed heat transfer research, very little information is available regarding geometries significant in heat treating applications. In this work, heat transfer to thin flat strips immersed in a fluidized bed is examined. This geometry is important in the steel strap manufacturing industry where many manufacturers use environmentally damaging molten lead baths to heat-treat their product. In order to determine the feasibility of a fluidized bed heat treating system as an alternative to the more hazardous lead-based process, an experimental investigation has been conducted in which Nusselt number data for flat strips with widths in the range of 6.35–25.4 mm are obtained using a laboratory-scale fluidized bed (310 mm diameter). Aluminum oxide sand particles in the range of dp=145–330 μm (50–90 grit) are used as the fluidized media within the fluidized operating range from 0.15Gmf to approximately 10Gmf. The strip orientation angle θo was also varied to establish the position from which maximum heat transfer is obtained. It was found that a decrease in particle diameter, an increase in fluidizing rate, and an increase in sample diameter resulted in an increase in Nusselt number. It was also observed that for the smaller samples tested, a maximum Nusselt number plateau was reached, at approximately G/Gmf=2.5. Finally, it was shown that an increase in θo (from 0 deg to 90 deg) resulted in an increase in Nusselt number. A correlation for the maximum Nusselt number was developed, providing excellent agreement within ±15%.

Role of dipole–dipole interaction on enhancing Brownian coagulation of charge-neutral nanoparticles in the free molecular regime

In contrast to van der Waals (vdW) forces, Coulombic dipolar forces may play a significant role in the coagulation of nanoparticles (NPs) but has received little or no attention. In this work, the effect of dipole-dipole interaction on the enhancement of the coagulation of two spherically shaped charge-neutral TiO(2) NPs, in the free molecular regime, is studied using classical molecular dynamics (MD) simulation. The enhancement factor is evaluated by determining the critical capture radius of two approaching NPs for different cases of initial dipole direction with respect to path (parallel∕perpendicular) and orientation with respect to each other (co-orientated∕counterorientated). As particle diameter decreases, the enhancement of coagulation is augmented as the ratio of dipole-dipole force to vdW force becomes larger. For 2-nm TiO(2) NPs at 273 K, the MD simulation predicts an average enhancement factor of about 8.59, which is much greater than the value of 3.78 when only the vdW force is considered. Nevertheless, as temperature increases, the enhancement factor due to dipole-dipole interaction drops quickly because the time-averaged dipole moment becomes small due to increased thermal fluctuations (in both magnitude and direction) of the instantaneous dipole moment.

A new approach for the detection of particle interactions for large-inertia and colloidal particles in a turbulent flow

The purpose of the paper is to present a new principle and a new algorithm for the direct numerical simulation of particle interactions within a turbulent flow. This approach has been developed in order to be able to compute agglomeration kernels with a numerical method which can still be applied at reasonable costs for very small colloidal particles. In this paper, classical algorithms are first tested and analyzed. They are shown to yield correct results but to require the use of time steps that are so small that they become intractable for colloidal particles. Their direct applications using large steps with respect to the relaxation time scale of the smallest particles reveal drastic errors that increase with the time step and with decreasing particle diameters. The new principle introduces the notion of continuous relative trajectories between possible collision partners and evaluates the exact probability for this trajectory to reach the minimum distance where two particles actually collide. Based on this new physical point of view and on the use of a probabilistic approach, a novel algorithm has been devised and numerical outcomes confirm that accurate predictions for the collision kernel are obtained independently of the particle diameter and for very large time steps. It is believed that the present ideas open interesting possibilities for the simulation of particle interactions over a whole range of particle behavior, from a ballistic to a diffusive regime, and can be extended to take into account new phenomena. Although present developments arise in the context of a numerical study, the new ideas that are introduced in this paper rely on the use of continuous stochastic bridges and, in that respect, propose a new approach to address physical issues of two-phase flow modeling.

Characteristics of filter cake exfoliation in upward ultrafiltration of nanoparticle suspensions.

Downward and upward ultrafiltration (UF) was performed using the suspensions of nanosized colloidal silica with different particle diameters and their filtration rates were compared. In downward UF, the filtration rate decreases as the particle diameter decreases because the specific filtration resistance of the filter cake becomes significantly higher. In contrast, the filtration rate in upward UF increases with the decrease in the particle diameter because the filter cake consisting of small particles is exfoliated much more easily under the influence of gravity than that of large ones. In order to evaluate the characteristics of the filter cake exfoliation, the steady filtration rate in the upward mode was measured. The steady filtration rate has a tendency to decrease with particle concentration as well as mean particle diameter. Therefore, when the small particles are added into a given concentration of large particle suspension, the mean particle diameter decreases and the total particle concentration increases due to the dosage of small particles. This results in a maximum of the steady filtration rate at a certain dosage of small particles. Moreover, an estimation equation was proposed for predicting the steady filtration rate in upward UF of colloidal silica suspensions with various mean particle diameters and total particle concentrations.

Estimation of the electrostatic charge of individual blowing-snow particles by wind tunnel experiment

AbstarctThere are some reports on the measurement of the charge-to-mass ratio of blowing-snow particles, but there are few studies concerned with individual snow-particle charge. We measured the charge-to-mass ratios using snow particles selected according to size, and discussed individual charges. Experiments were conducted in a cryogenic wind tunnel. Charge-to-mass ratios measured in our experiment were all negative and their absolute values tended to increase with a decrease in particle diameter. Individual snow-particle charges were calculated from the average of particle diameter distributions. The charges were all approximated by the power function of diameter at each temperature. Assuming that the coefficient of these approximations is a function of air temperature, we could easily predict the individual snow-particle charge.