Aerosol classification by electric mobility: apparatus, theory, and applications

An improved version of the Hewitt (differential) electric mobility analyzer was developed and its classifying characteristics were determined theoretically. The central mobility of the classified aerosol was found to be (q_c + q_m)/4πΛV, where q_c and q_m are the clean air and main outlet flows, respectively, Λ is a geometric factor, and Λ is the center rod voltage. The half-width of the mobility band was found to be (q_a + q_s)/4πΛV, where q_a and q_s are the aerosol and sampling outlet flows, respectively. These expressions were verified by the tests with a monodisperse aerosol of known size and low charge.

A major advantage of this device is that the classified aerosol fraction remains airborne, ready for further use or analysis. Thus, one application of the device is the production of monodisperse test aerosols of known size, charge, and concentration by classification of a polydisperse aerosol. Other current applications include accurate measurement of particle electric mobility moments and high-resolution particle size analysis for polydisperse aerosols in the 0.005–1.0 μm size range.     

A model for kinetically controlled internal phase segregation during aerosol coagulation

In previous studies of particle growth, we have synthesized binary metal oxide aerosols and have observed the evolution of internal phase segregation during growth of molten nanodroplets. We describe a new formulation of the aerosol general dynamic equation (GDE) that incorporates phase segregation in a binary aerosol. The model assumes that complete phase segregation is the thermodynamically favored state, that no thermodynamic activation energy exists, and that the segregation process is kinetically controlled. We develop a GDE formulation that involves the solution of a distribution function N_n(V), where N_n(V) is the number density of aerosols with volume V and n phase domains (which we might think of as enclosures). The GDE is solved using a two-dimensional sectional model, under the assumption that the phase coalescence of the minority phase is controlled by Brownian coagulation. For the purposes of these initial studies, the rate laws governing the enclosures (minority phase) assume a monodisperse particle size distribution. The dynamical behavior of such a system is presented.     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.     

Synthesis of ordered small pore mesoporous silicates with tailorable pore structures and sizes by polyoxyethylene alkyl amine surfactant

Ordered mesoporous silicates with tailorable pore structures and small pore sizes have been synthesized by using polyoxyethylene alkyl amine surfactant PN-430 [CH₃(CH₂)₁₇N(EO)_x(EO)_y, x + y = 5] as a structure-directing agent under acidic condition. Two-dimensional (2-D) hexagonal (p6mm) mesoporous silicates have been prepared via an evaporation-induced self-assembly (EISA) process. The N₂ sorption isotherms show that the product has a small uniform pore size distribution of 1.8 nm by BJH model, a BET surface area of 730 m²/g and a pore volume of 0.36 cm³/g. 3-D cubic (Pm-3n) mesoporous silicate with small uniform pore size (1.76 nm) can also be prepared at high concentration of PN-430 by EISA method in tetrahydrofuran solvent. The solvothermal post-treatment by n-hexane at 70 °C for 3 d to the above material results in the phase transition of the mesostructure from Pm-3n to P6₃/mmc based on XRD and TEM analyses. In comparison, by using nonionic oligometric alkyl-ethylene oxide surfactant such as Brij 78 (C₁₈H₃₇EO₂₀) or Triton X-100 (CH₃C(CH₃)₂CH₂C(CH₃)₂C₆H₄ EO₁₀) as co-templates, high-quality hexagonal (p6mm) small pore mesoporous silicates have also been prepared in ethanol media. Our results show that the blend templates composed of PN-430 and a small amount of nonionic surfactant can increase the efficiency of organic and inorganic hybrid species assembly, improve the quality of the structural regularity, and decrease the pore size to about 1.65 nm.     

Microscopic and macroscopic atomization characteristics of a pressure-swirl atomizer,injecting a viscous fuel oil

Combustion of heavy fuels is one of the main sources of greenhouse gases, particulate emissions, ashes, NOxand SOx. Gasification is an advanced and environmentally friendly process that generates combustible and clean gas products such as hydrogen. Some entrained flow gasifiers operate with Heavy Fuel Oil(HFO) feedstock. In this application, HFO atomization is very important in determining the performance and efficiency of the gasifiers.The atomization characteristics of HFO(Mazut) discharging from a pressure-swirl atomizer(PSA) are studied for different pressures difference(Δp) and temperatures in the atmospheric ambient. The investigated parameters include atomizer mass flow rate( _m), discharge coefficient(CD), spray cone angle(θ), breakup length(Lb), the unstable wavelength of undulations on the liquid sheet(λs), global and local SMD(sauter mean diameter) and size distribution of droplets. The characteristics of Mazut sheet breakup are deduced from the shadowgraph technique. The experiments on Mazut film breakup were compared with the predictions obtained from the liquid film breakup model. Validity of the theory for predicting maximum unstable wavelength was investigated for HFO(as a highly viscous liquid). A modification on the formulation of maximum unstable wavelength was presented for HFO. SMD decreases by getting far from the atomizer. The measurement for SMD and θ were compared with the available correlations. The comparisons of the available correlations with the measurements of SMD andθ show a good agreement for Ballester and Varde correlations, respectively. The results show that the experimental sizing data could be presented by Rosin-Rammler distributions very well at different pressure difference and temperatures.     

A moment methodology for coagulation and breakage problems: Part 2—moment models and distribution reconstruction

Population balances for simultaneous coagulation and breakage (and their analogs, e.g., polymerization and depolymerization) are employed in describing many systems (e.g., aerosols, powders and polymers), and many unit operations including reactors, crystallizers and size reduction/enlargement equipment. The population balance equations for homogeneous coagulation rate, power-law breakage rate and self-similar daughter particles are solved in moment form under a polynomial interpolative closure rule. Limiting steady-state analytical approximations for the distribution function of the very small particles are incorporated into basis sets enabling reconstruction of the distributions from their moments utilizing a nonlinear regression technique.     

Effect of macromolecular length on anisotropic scattering of light in an electric field

Light scattering by monodisperse solutions of rigid rod-like anisotropic macromolecules, with linear dimensions l of the order of incident wavelength λ, oriented in an external d.c. electric field, →E has been analysed. The relative variations δV^E_v, δH^E_v, δV^E_h, δH^E_h of the scattered light components are discussed for the three values [l/λ] = 1, 0·5, 2, and various reorientation parameters, p = [μE/kT] of the permanent dipole moment μ and q = [(₃ − ₁)E²/2kT] of the moment induced by the principal polarizabilities ₁ = ₂ ≠ ₃. The saturation orientation field strength has been calculated for certain macromolecules with the aim of determining their optical anisotropy numerically.     

Transport numbers and oxygen permeability of SrCe(Y)O3-based ceramics under oxidising conditions

Partial conductivities in the SrCe(Y)O_3−δ system have been studied in oxidising conditions in the temperature range 923–1273 K. Compositions with variable Y content (5 and 10 at.%), Sr deficiency (3 at.%), and with the addition of Fe₂O₃ as sintering aid (2 mol%) were analysed. A modified Faradaic efficiency method and oxygen permeation measurements were employed to appraise the oxide-ionic transport. Oxide-ion transference numbers in air lie in the range 0.19–0.80 and decrease with increasing temperature in the range 973–1223 K. Modelling of total conductivity as a function of oxygen partial pressure (p(O₂)) confirmed that protonic transport is minor under the studied conditions. SrCe_0.95Y_0.05O_3−δ exhibits greater oxide-ion conductivity than SrCe_0.9Y_0.1O_3−δ, indicative of dopant–vacancy association at high dopant contents. Conversely, oxygen permeability is slightly higher for SrCe_0.9Y_0.1O_3−δ as a result of faster surface-exchange kinetics. The oxygen flux through Fe-free membranes is dominated by the bulk in low p(O₂) gradients, when the permeate-side p(O₂) is higher than 0.03 atm, but surface exchange plays an increasing role with increasing p(O₂) gradient. Addition of Fe₂O₃ to SrCe(Y)O_3−δ lowers the sintering temperature by 100 K but results in the formation of intergranular second phases which block oxide-ionic and electronic transport, and thus oxygen permeation. The average thermal expansion coefficients (TECs) are (10.8–11.6) × 10⁻⁶ K⁻¹ in the temperature range 373–1373 K for all studied compositions.     

Conformation of isotactic polystyrene (IPS) in the bulk crystallized state as revealed by small-angle neutron scattering

Neutron scattering experiments have been performed on isotactic polystyrene (IPS) samples in the bulk crystallized state (T_{crystallization} = 185°C). The determination of the conformation of tagged chains ranging from 2.5 × 10⁵ to 7 × 10⁵ has been undertaken on two different hydrogenated IPS matrices. A matrix of usual molecular weight (M_w = 4 × 10⁵) leads to results which do not agree with Flory's model. In this case, measurements on radius of gyration R_g show on the one hand an important increase of this parameter (40%) with increasing crystallinity for the highest molecular weight tagged chains and on the other hand a variation with molecular weight like M^0.78. These results are interpreted with a schematic model involving a long crystalline sequence incorporated in the monocrystal along the 110 plane and two amorphous wings. Such an assumption is confirmed by the scattering behaviours in the intermediate range. On the other hand, by using an IPSH matrix of very high molecular weight (M_w = 1.75 × 10⁶), and the same tagged chains previously considered, a very weak variation of R_g with increasing crystallinity is observed. This leads to consider in this case Flory's conformation which is corroborated by data obtained in the intermediate range.     

Hydrotreating properties of mixed NbxMo1−xS2 alumina supported catalysts

Niobium-molybdenum disulfide solid solution (Nb_xMo_1−xS₂) has been prepared in a dispersed state on gamma alumina. The existence of this solid solution supported on alumina carrier has been proven with the help of EXAFS technique. The catalytic properties of these materials have been studied in hydrogenation and hydrodesulfurization reactions. Interestingly, as already observed for niobium sulfide, the activity of the Nb_xMo_1−xS₂ solid solution (HDS of DBT, P_tot=33 bar) is not decreased in the presence of H₂S up to p(H₂S)=200 Torr, at least up to x=0.4.     

用新的路径定位指数和神经网络研究多溴联苯醚理化性质

基于溴取代基及共轭母体的结构特征,定义一种新的路径定位指数^mP,并计算了209种多溴联苯醚分子的电性拓扑状态指数E₉和电性距离矢量M₂₆,这3个指数对有机污染物呈现出良好的结构选择性。采用多元回归方法对多溴联苯醚（PBDEs）的色谱保留时间（t_R）、正辛醇/空气分配系数（lgK_OA）、超冷流体蒸气压（lgP_L）及其毒性等性质与分子结构指数进行关联,建立的4个预测模型的相关系数分别达到0.991、0.997、0.998和0.904,标准偏差分别为0.031、0.104、0.100和0.358。将3个指数作为BP神经网络的输入层神经元,采用不同的网络体系结构,获得了令人满意的预测理化性质的神经网络模型,所得结果明显优于多元回归方法,结果显示多溴联苯醚的理化性质与⁰P、E₉和M₂₆具有良好的非线性关系。     

Extended log-normal method of moments for solving the population balance equation for Brownian coagulation

An extended log-normal method of moments (ELNMOM) is presented in this study for solving the population balance equation (PBE) for Brownian coagulation. The method is an extension of the log-normal method of moments (LNMOM) proposed by Lee in 1983. The ELNMOM uses the superposition of log-normal subdistributions to represent the size distribution. Unlike previous modal studies, the subdistributions are not independent modes but flexible components in this study and the closure of this method is achieved by introducing additional higher-order moment equations. Based on some simplifying assumptions, the ELNMOM is implemented with only four adjustable parameters for a preliminary exploration. The method is then validated by comparing the size distribution parameters predicted by this method with those predicted by the LNMOM and other numerical methods for Brownian coagulation in the continuum regime and the free-molecular regime. The results show that the ELNMOM more accurately predicts the total particle number concentration, the geometric standard deviation and the geometric mean particle volume than the LNMOM while not taking much more computation time.

Copyright © 2019 American Association for Aerosol Research     

Universality of properties of coil-globule transitions in different two-dimensional lattice models of a macromolecule

Using a Monte-Carlo method, we study the behaviour of different lattice models of a linear macromolecule in the θ-point region. Paying most attention to the testing of new theoretical concepts of the two-dimensional θ point^1,2, we give a new interpretation of some numerical results of our previous work^3,4 and generalize others. We confirm the assumption of the universality of the value of the tricritical exponent v_t = 4/7. The values of v_t for a self-avoiding walk (SAW) on triangular, square and honeycomb lattices as well as for two special models, viz. infinitely prolonging self-avoiding walks (IPSAW)³ and infinitely growing self-avoiding walks with nearest-neighbour interactions (IGSAWN)⁵, lie between 0.56 and 0.59. The slight differences between these results can be explained by the effect of the corrections to scaling, which have different values for different models. The values of the crossover exponent _t are confined between 0.42 and 0.6, which is not in complete contradiction with the value _t = 3/7 for the θ point, proposed elsewhere², but differ from our previous result _t = 0.6 ± 0.1 obtained earlier^3,4 without extrapolation to the limit N → ∞, where N is the length of a chain. The values of the free-energy exponent γ_t determined in the present work lie between 0.98 and 1.07, and, thus, do not coincide with the value of γ_t = 8/7 proposed by others². The value of γ_1t = 0.5 ± 0.05 that we obtained for a polymer confined in a half-space is in complete contradiction with the above result² for the θ point. As a whole, our results are in good agreement with recent work^6,7 using a similar technique for shorter SAWs on a square lattice.     

Determination of the smallest particle size detectable in condensation nucleus counters by observation of the coagulation of SO2 photo-oxidation products

The method proposed by Walter et al. (1973) for determining the smallest particle size detectable in condensation nucleus counters (CNC) was conducted experimentally. A dynamic flow system was developed for observation of the particle concentration changes due to coagulation for particles produced by heteromolecular nucleation of H₂SO₄ and water vapor through the irradiation of SO₂ and carrier gas with u.v.-light. Experiments indicate the presence of thermal coagulation as well as other processes. Evidence was found to isolate the coagulation effects from other processes. A smallest particle size detectable in condensation nucleus counters with standard expansion ratio thus was determined to be r_L = 1.6 × 10⁻⁷ cm.     

Polymers in mixed solvents: application of the new representation of viscosity data as a function of molecular weight

The relation proposed between the intrinsic viscosity and the molecular weight of a polymer^1,2 (1/[η]versus 1/M^1/2), has been applied in this paper in cases when the polymer is dissolved in a binary solvent mixture. We have then shown that even in this case we can calculate in a very accurate way the molecular weight of the polymer from its intrinsic viscosity, especially in the molecular weight range where the Mark-Houwink-Sakurada equation is the least applicable (M_w < 150 000).     

Electrosorption and inhibition properties of p-norborn2-yl phenolate ions at the mercury/solution interface

The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements.

Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°_A = −32.5 ± 1 kJ mol⁻¹. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated.

At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant.

The electrode reaction S₂O²⁻₈ + 2e⁻ → 2 SO²⁻₄ is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log k_s (k_s apparent rate constant) on ln c_A and π (π = surface film pressure), respectively, has been found.     

Modeling and Control of a Titania Aerosol Reactor

We focus on modeling and control of an aerosol flow reactor used to produce titania powder. We initially present a detailed population balance model for the process which accounts for simultaneous nucleation, Brownian and shearinduced coagulation, and convective transport and describe the spatio-temporal evolution of the aerosol volume distribution. Then, under the assumption of lognormal aerosol volume distribution, the method of moments is employed for the derivation of a model that describes the evolution of the three leading moments of the volume distribution. The moment model, together with the fundamental model that describes the temperature in the reactor and concentrations of the gas-phase species, are subsequently used to synthesize a nonlinear output feedback controller which manipulates the temperature of the reactor wall to achieve an aerosol size distribution in the outlet of the reactor with desired geometric average particle diameter. The nonlinear controller is successfully implemented on the process model and is shown to deal effectively with external disturbances.     

Insight into solute-solute and solute-solvent interactions of semicarbazide hydrochloride in water and D-glucose/D-sucrose+water solutions at temperatures (293.15 to 318.15) K

The solute-solute and solute-solvent interactions of drug semicarbazide hydrochloride with carbohydrates (D-glucose/D-sucrose) are investigated by using volumetric, viscometric and acoustic properties. The measurements of the densities ρ, ultrasonic speeds u, and viscosities η. of semicarbazide hydrochloride in 5% and 10% D-glucose/D-sucrose+water (w/w) solutions were carried out at temperatures (293.15-318.15) K and at pressure, p=101 kPa. The apparent molar volumes, V_ϕ, limiting apparent molar volumes,V_ϕ°, apparent molar compressibilities, K_{s, ϕ}, limiting apparent molar compressibilities, K_s,ϕ°, partial molar expansibilities, E_ϕ°, transfer volumes, V_ϕ,tr° and transfer compressibilities, K_s,ϕ,tr° have been calculated from the experimental data. The viscosity data were examined by using the Jones-Dole equation and the viscosity A and B coefficients were evaluated. The results are discussed in terms of solute-solute and solute-solvent interactions in these solutions. The structure making/breaking ability of semicarbazide hydrochloride is examined using the sign of temperature derivative of B-coefficient, dB/dT.     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D_e) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X_o). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

Effect of electro-chemical properties of sodium salts of various anions on their diffusional parameters in symmetrical cellulose acetate membranes

A relation was obtained between electro-chemical properties of sodium salts (NaCl, NaBr, and Na₂SO₄), and the thermodynamic property of permeability in symmetrical cellulose acetate membranes, the distribution coefficient K and the kinetic property, the overall diffusion coefficients D. K and D were obtained by the method we proposed using measured unsteady- and steady-state dialysis data. The K values increase with the increase of water content and are in the range of 10⁻² for sodium halides and 10⁻³ for Na₂SO₄. D is found to increase with the increase of the solute concentration, and the extrapolated values of D to zero concentration D⁽⁰⁾ are obtained as 0.015–0.03 μm²/s and increase with the increase of water content in the membrane. D can be divided into the concentration independent diffusion coefficients in the dense part of the membrane D_d and in the porous D_p, applying a two-part (perfect or dense and imperfect or porous) model of the membrane. Contrary to D_d, D_p increases with the increase of W_w and can be correlated as D_p,c = _d exp (γ × W_w). It is shown that the averaged D_d, _D increases with the increase of the quantity of the ionic mobility u of the solutes at infinite dilution divided by valence, and that the parameter γ increases with the increase of the ionic mobility u. The value of K increases slightly with the increase of water content and decreases with the increase of the Flory—Huggins parameter χ. The Flory—Huggins parameter χ is calculated from the measured values of distribution coefficients and data obtained from the literature. And it was found that the gradient of linear decrease of χ (λ_cation) depends on equivalent ionic conductivity of anion of salt, λ_an.