Effective density of airborne particles in a railway tunnel from field measurements of mobility and aerodynamic size distributions

The objective of this study is to investigate the particle effective density of aerosol measurements in a railway tunnel environment. Effective density can serve as a parameter when comparing and calibrating different aerosol measurements. It can also be used as a proxy parameter reflecting the source of particles. Effective density was determined using two different methods. Method one defined it by the ratio of mass concentration to apparent volume size distribution. Method two relied on a comparison of aerodynamic and mobility diameter size distribution measurements. The aerodynamic size range for method one was 0.006–10?µm, and for method two, it was 10–660?nm. Using the first method, a diurnal average value of about 1.87?g/cm³ was observed for the measurements with tapered element oscillating microbalance (TEOM) in tandem with aerodynamic particle sizer?+?scanning mobility particle sizer (SMPS), and 1.2?g/cm³ for the combination of TEOM with electrical low pressure impactor plus (ELPI+) in the presence of traffic. With method two, the effective density was 1.45?g/cm³ estimated from the size distribution measurements with ELPI?+?and fast mobility particle sizer (FMPS), and 1.35?g/cm³ from ELPI?+?in tandem with SMPS. With both calculation methods, the effective density varied for conditions with and without traffic, indicating different sources of particles. The proportion of particles with small sizes (10–660?nm) had a significant effect on the value of the effective density when no traffic was operating. The responses of different instruments to the railway particle measurements were also compared.

Copyright © 2018 The Authors. Published with license by Taylor &; Francis Group, LLC     

A note on the aerodynamic diameter and the mobility of non-spherical aerosol particles

The aerodynamic diameter of a non-spherical aerosol particle is primarily related to the final settling velocity of the particle. The aerodynamic diameter is not obtained directly from mobility measurements by formally calculating a sphere diameter from the mobility equation for a spherical particle. Instead, a correction factor involving the dynamic shape factor of the non-spherical particle must be applied.     

Development of a toroidal-shaped differential mobility analyzer for effective measurements of airborne particles: Experiment and modeling

Abstract

A toroidal-shaped differential mobility analyzer (DMA), called toroidal Hanyang-DMA (toroidal Hy-DMA), was developed for particle characterization. The height, width, and weight of the newly developed toroidal Hy-DMA are 8?cm, 14?cm, and 1.2?kg, respectively, indicating that it is much more compact and lighter than the TSI long-DMA; nevertheless, the classifiable particle size range is up to 400?nm. Therefore, the toroidal Hy-DMA can be useful for many applications in a limited space owing to its small size. The performance of the Hy-DMA was evaluated using tandem differential mobility analyzer (TDMA) experiments with two identical Hy-DMAs and numerical simulations using a single-particle tracking analysis in a Lagrangian framework. To simulate particle behaviors, a flow-rate-weighted particle injection method, which is more realistic, was employed, and the proposed particle tracking method can be widely applied to any non-plug flow conditions. The obtained experimental data and numerical results of central particle sizes are consistent with each other. Empirical and numerical transfer functions of the toroidal Hy-DMA were obtained and compared with those of other types of well-known DMAs. It is concluded that the toroidal Hy-DMA has an empirical transmission probability ranging from 0.5 to 0.9 and a sizing resolution ranging from 5.5 to 9.0, which indicates acceptable performance in classifying monodisperse particles within the test size range of 20 to 400?nm.

Copyright © 2019 American Association for Aerosol Research     

Determination of non-spherical particle size distribution from chord length measurements. Part 2: Experimental validation

In this paper, the theory on the translation of a measured chord length distribution (CLD) into its particle size distribution (PSD), which was developed in the first part of this study [Li and Wilkinson, 2005. Determination of non-spherical particle size distribution from chord length measurements. Part 1: theoretical analysis. Chemical Engineering Science 60, 3251-3265], has been validated using experimental results. CLDs were measured using the Lasentec focused beam reflectance measurement (FBRM) with three different materials, spherical ceramic beads and non-spherical plasma aluminium and zinc dust particles. Meanwhile, the particle shape and PSD of each material were also investigated by image analysis (IA). Comparison of the retrieved PSDs with the measured PSDs by IA shows that the PSD can be retrieved from a measured CLD successfully using the proposed iterative nonnegative least squares (NNLS) method based on the PSD-CLD model.     

Determination of non-spherical particle size distribution from chord length measurements. Part 1: Theoretical analysis

In this paper, extensive theoretical studies are described on two important issues in translating a chord length distribution (CLD) measured by FBRM instrument into its particle size distribution (PSD) including PSD-CLD and CLD-PSD translation models for general non-spherical particles. Analytical solutions to calculate the PSD-CLD models for spherical and ellipsoidal particles are developed. For non-spherical particles, a numerical method is given to calculate the PSD-CLD model. The iterative non-negative least squares (NNLS) method is proposed in the CLD-PSD model, because of its many advantages converting measured CLD into its PSD, such as insensitivity to measurement noise and particle shape. The effectiveness of the proposed methods is validated by extensive simulations.     

Evaporation from non-spherical particles: the equivalent-volume and inscribed sphere approximations for nearly spherical particles

Although numerical results for evaporation rates from arbitrarily shaped particles have been recently reported in the literature, it remains of interest to explore construction and accuracy of approximate analytical expressions that are simple and of general use. We have analyzed the popular equivalent-volume approximation and also the inscribed sphere approximations in this context, using a technique due to Zhang and Stone (J. Fluid Mech. 367 (1998) 329) who had studied rotatory oscillations of nearly spherical bodies. Comparison of the approximate results with accurate numerical results shows that both these approximations are quite useful. The equivalent-volume sphere approximation is particularly attractive as the error is of the order ε², where ε is a measure of departure from the spherical shape.     

Tuning the particle size and charge density of the crosslinked polystyrene particles

We report the synthesis of charged spherical colloidal particles of poly [styrene‐(co‐2‐propene sulfonic acid)] crosslinked with divinylbenzene by emulsion polymerization. The effects of concentration of both the emulsifier and initiator on the polymerization, particle size, and charge density are studied. The particle size is found to be dependent on both the emulsifier and initiator concentration and their power dependencies are different. Below critical micelle concentration (CMC), the particle size varies significantly within a small range of emulsifier concentration. In contrast, particle size decrease is not very pronounced at the heterogeneous (micellar) particle nucleation regime where the emulsifier concentration is well above of the CMC. The power dependencies of the number of particles on surfactant concentration are explained in the light of conversion–time profile of the polymerization. The surface charge density of the colloidal particles also varies with both the emulsifier and initiator concentration. Both the particle size and charge density show an inverse relation with the molecular weight of the polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

On measuring the density of fine particles by pycnometry

Measurement of the density of fine powders by pycnometry is subject to error especially when the particles are porous. Pycnometric liquid may enter the particle pores to an unknown extent or may not enter all interstitial space. The application of pressure may crush porous particles altering their original density. In this paper the different effects are examined analytically and equations and graphs are presented to show the extent of potential error. Experimental results are reported which show that with particle size less than about 100 μ m mercury pycnometry can give misleading results because of incomplete interstitial penetration.     

Spherical porous carbon particles derived from suspensions and sediments of resorcinol-formaldehyde particles

The goal of this study is the completion of the parameter field of resorcinol-formaldehyde solutions towards the regime of non-monolithic phases. For low sodium carbonate concentration and low mass content of resorcinol and formaldehyde in the starting solution the formation of spherical particles rather than monolithic gels is observed. The organic precursors were converted into carbon powders by pyrolysis. The resulting carbon particles were characterized by scanning electron microscopy (SEM), nitrogen sorption and small-angle X-ray scattering (SAXS). The study shows that carbonization of the organic particles results in spherical carbon particles with a micropore volume of about 0.28 cm³/g. The composition of the starting solution, however, strongly affects the external surface area as determined from sorption data for the organic as well as for the corresponding carbon particles; the values derived can be converted into average diameters of spherical particles ranging from 30 nm to 5 μm. Complementary SEM and SAXS measurements confirm these findings. A diameter of 5 μm appears to be the upper size limit in particle size forming, while 30 nm spheres develop near the formation of a continuous gel at relatively high sodium carbonate concentrations.     

The effective density and fractal dimension of particles emitted from a light-duty diesel vehicle with a diesel oxidation catalyst

A differential mobility analyzer (DMA) and a Couette centrifugal particle mass analyzer (Couette CPMA) were used to measure the effective density and fractal dimension of particles emitted from a light-duty diesel vehicle fitted with a diesel oxidation catalyst (DOC). It was found that at high engine loads, the DOC increased in temperature, sulphate levels in the particulate matter increased, and a transient nucleation mode was observed. The increase in sulphate levels resulted in a drastic increase in the effective density and fractal dimension of the particles. At low engine loads (8–15%), sulphate levels were much lower, no nucleation mode was present and the fractal dimension varied from 2.22 to 2.48, which is in good agreement with previous studies. At 40% load, sulphate levels were much higher and the fractal dimension was 2.76.     

Effect of grain size and density of spray-pyrolyzed hydroxyapatite particles on the sinterability of hydroxyapatite disk

The effect of grain size and density of hydroxyapatite particles, which were prepared by different spray-pyrolysis temperatures, on the sinterability of hydroxyapatite disk was investigated. Calcium phosphate solution (Ca/P ratio of 1.67 and 0.1 M concentration) was prepared by reacting calcium nitrate tetrahydrate and diammonium hydrogen phosphate solutions, and adding nitric acid. Spray-pyrolysis was carried out at 900 °C, 1200 °C, and 1500 °C at a carrier gas flowing rate of 10 L/min. The particles synthesized at 900 °C were large, hollow spheres with a hole at the outer surface, a broad size distribution, but had small grain sizes. Conversely, the particles synthesized at 1500 °C were small, solid spheres with a narrow size distribution, but had large grain sizes. The particles synthesized at 1200 °C had intermediate properties. A sinterability test conducted at 1100 °C for 1 h demonstrated that small and dense particles with large grain sizes showed a higher relative sintered density compared with large and hollow particles with small grain sizes. The results were explained in terms of the grain size and density of a particle, which were inversely and proportionally affected to sinterability. The practical implication of these results is that highly sinterable hydroxyapatite powders can be synthesized through spray-pyrolysis at a high temperature under a fixed initial concentration of calcium phosphate solution and flow rate of carrier gas.     

Measuring the effective density, porosity, and refractive index of carbonaceous particles by tandem aerosol techniques

The physical properties of carbonaceous aerosol particles are often of interest but are difficult to determine from a single measurement. In this study, we used tandem aerosol measurement techniques to measure the effective physical properties, namely the effective density, porosity, and effective complex refractive index of spheroid aggregated and porous carbonaceous aerosol particles. An in-flight measurement system, composed of a differential mobility analyzer (DMA) followed by either an aerosol particle mass analyzer (APM) or a laser particle counter-pulse height analyzer (LPC–PHA), was constructed and used to examine shape-controlled and porosity-controlled carbonaceous particles produced by a spray-drying process. The effective density and porosity were inferred from tandem measurements in which particles were first mobility-classified by the DMA and subsequently mass classified in the APM. The effective refractive index of the particles was inferred from tandem DMA–LPC–PHA measurements in conjunction with Mie Theory. The measured effective density and porosity of the carbonaceous particles ranged from 695.0 to 1399.9 kg/cm³ and 15.2% to 64.3%, respectively. Furthermore, the real and imaginary parts of the effective complex refractive index were between 1.430 and 1.736 and between 0.035 and 0.125, respectively. Both the real and imaginary parts decreased with increasing particle porosity.     

Mixing and segregation in a liquid fluidized bed of particles with different size and density

Experimental studies have been carried out on fluidization of irregular particle mixtures of different size and density. The mixing and segregation phenomena could be interpreted on the basis of the diffusion model of Kennedy and Bretton. The dependence of computed particle dispersion coefficient on liquid velocity, particle density and size has been discussed.     

Synthesis and surface measurements of surfactants derived from dehydroabietic acid

Dehydroabietates with poly(ethylene oxide) chains of average m=12, 17, and 45 units [DeHab(E) _m ] were synthesized. The adsorption at the liquid-vapor interface was measured, and the adsorbed amount and critical micelle concentrations (CMC) were determined. The foamability, the foam stability, wetting properties, and cloud points, with and without salt content, were studied. The results were compared with common linear alkyl ethoxylates, nonylphenol ethoxylates, and cholesterol ethoxylates. The dehydroabietic acid as hydrophobe was found to result in the same CMC as a linear dodecyl chain. DeHab(E)₄₅ was found to be insoluble above 400 mg/L, but the surface tensions at lower concentrations were similar to those of the C_11–13E_38–40 surfactants, which exhibit CMC in aqueous media. The foaming behavior of the DeHab(E)₁₂ and DeHab(E)₁₇ surfactants was about the same as for common linear C _n E _m surfactants. The foamability as well as the foam stability increased with ethylene oxide (EO) chain length. The cloud point was depressed by increased salt concentration and increased with the number of EO units in the head group. The cloud point was significantly lower than for the corresponding surfactant with a dodecyl chain with similar EO chain length. The wetting results, obtained by measuring the contact angle at similar surface tensions, indicate that surfactants of the DeHab(E) _m type are more efficient wetting agents than both disaccharide sugar surfactants and C _n E _m type surfactants.     

Attrition behavior of fine particles in a fluidized bed with bimodal particles: Influence of particle density and size ratio

To process the solid particulates in fluidized bed and slurry phase reactors, attrition is an inevitable consequence and is therefore one of the preliminary parameters for the catalyst design. In this paper, the mechanical degradation propensity of the zeolite catalysts (particles) was investigated in a bimodal distribution environment using a Gas Jet Attrition — ASTM standard fluidized bed test (D-5757). The experimentation was conducted in order to explore parameters affecting attrition phenomena in a bimodal fluidization. In a bimodal fluidization system, two different types of particles are co-fluidized isothermally. The air jet attrition index (AJI) showed distinct increases in the attrition rate of small particles in a bimodal fluidization environment under standard operating conditions, in comparison with single particle. A series of experiments were conducted using particles of various sizes, with large particles of different densities and sizes. Experimental results suggest that the relative density and particle size ratio have a significant influence on attrition behavior during co-fluidization. Therefore a generalized relationship has been drawn using Gwyn constants; those defined material properties of small particles. Moreover, distinct attrition incremental phenomenon was observed during co-fluidization owing to the change in collision pattern and impact, which was associated with relative particle density and size ratios.     

Determination of thermal parameters of non-spherical particles in a packed bed from svstem response analysis in the time domain

The thermal conductivity and the particle-to-fluid heat-transfer coefficient for peanut-shaped polyester particles in a packed bed were determined simultaneously using the pseudo-random binary noise sequence (PRBNS) response technique. The modified Dispersion-Concentric (D-C) model was applied to beds packed with the non-spherical particles. A time domain method, using the convolution integral, was developed for removing the effects of the bed ends and the transducer time lag on the experimental responses. Parameter estimation was performed in the time domain, using a simplex method to fit the thermal response calculated from the parametric D-C model to the experimental response curve. The particle-to-fluid heat transfer coefficient in the bed was determined to be 106 W/m². K at an interstitial fluid velocity of 2.0 m/s. The thermal conductivity of polyester was 0.22 W/m. K at 313 K.