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© 2017, Akadémiai Kiadó, Budapest, Hungary. 137 Cs and 241 Am extraction with perchloroethylene solutions of O-substituted p-alkylcalix[8]arenes (alkyl: tert-butyl, iso-nonyl) from carbonate-alkaline media is studied. Dependence of distribution ratios on pH values of the aqueous phase in the range 11–13.9 and on the nature of functional groups in the calixarene platform is confirmed. Composition of cesium and americium solvates with calix[8] arenes is determined. Tert-butylcalix[8]arene with oxybis(ethane-1,2-diyl) bridging group possesses superior efficiency towards cesium in alkaline media. The most efficient extractants for americium are “mixed” iso-nonyl-tert-butylcalix[8] arenes with ethane-1,2-diyl and oxybis(ethane-1,2-diyl) bridging groups.

© 2017, Pleiades Publishing, Inc. The effect of γ-irradiation of tert-butylthiacalix[4]arene (TCA) solutions in m-nitrobenzotrifluoride (NBTF) and tetrachloroethylene (TCE) on the extraction of 241 Am from alkaline carbonate solutions was studied. TCA itself remains stable upon γ-irradiation of its solutions in NBTF to a dose of 200 kGy, but the diluent undergoes strong degradation. The radiation resistance of TCA in TCE is considerably lower: A dose of 70 kGy causes complete degradat ion of TCA. In the TCA–TCE–aqueous phase system, sulfate ions appear upon γ-irradiation as the final product of the extractant radiolysis. A large number of γ-radiolysis products of TCE and TCA were detected by HPLC and GCMS. The products of radiolysis of TCA in TCE, compared to the initial extractant, have lower molecular mass and higher polarity. The results show that chlorinated diluents are not promising diluents for thiacalixarene in extraction processing of alkaline high-level waste.

© ISUCT Publishing. The recovery of long-lived radionuclides from liquid radioactive wastes with subsequent immobilization and disposal significantly reduces radiological risks in the nuclear industry. At the Savannah River Site (USA), the functionalized calixarene bis(dimethyloctyl-oxy)calix[4]arenebenzocrown-6 (MaxCalix) was successfully used as selective extractant to separate cesium-137 from alkaline radioactive wastes. At the Mayak PA (Russia), the alkaline radioactive wastes include actinides, essentially americium, in addition to cesium-137, which also should be recovered. To separate cesium and americium from alkaline solutions, the simple tert-butylcalix[8] arene could be used, if it was not so poorly soluble in organic solvents. The aim of this study was to synthesize mixed p-alkylcalix[8] arenes with tert-butyl and isononyl groups taken at various ratios and to examine their applicability to extract cesium and americium from alkaline solutions. Starting from commercially available p-isononylphenol we have synthesized and characterized three mixed tert-butyl-isononylcalix[8] arenes with the tert-butyl to isononyl group ratio taken as 6:2, 4:4, and 2:6. The solubility of these mixed tert-butyl-isononylcalix[8]arenes in tetrachloroethylene ranges from 0.01 to 0.08 M, which is 3 to 8 times higher than that of p-tert-butylcalix[8] arene. The extraction of 137 Cs and 241 Am from alkaline-carbonate solutions with mixed p-alkylcalix[8]arenes in tetrachloroethylene was studied. For all the extractants, the maximal extraction of cesium and americium was observed in the pH range 13–14. Americium is extracted at lower pH since, unlike cesium, it forms very strong hydroxo complexes at high pH values. The composition of the solvates formed by the calixarenes with the radionuclides in the organic phase was determined using the equilibrium shift method (for trace amounts of the radionuclides) and the saturation method (extraction isotherm). The results obtained by the equilibrium shift method revealed dominant formation of solvates, in which the p-alkylcalix[8] arene binds 1–2 cations of cesium or americium. The saturation method suggests formation of solvates containing up to four cesium cations per an p-alkylcalix[8] arene molecule. Step-by-step substitution of the tert-butyl groups in p-alkylcalix[8] arene for the isononyl groups leads to decreasing extraction of both cesium and americium. For cesium, a small monotonic decrease in the extraction power of p-alkylcalix[8]arenes was observed: the difference in the distribution ratios between the tert-butyl and isononyl derivatives of calix[8] arene was less than two. The highest extractability of americium was observed with the mixed calix[8]arene containing two isononyl groups, and the difference in the distribution ratios was above 20. Interesting results were obtained when comparing the extraction of americium with freshly prepared and aged tetrachloroethylene solutions of the mixed calix[8] arene containing two isononyl groups. The americium distribution ratios obtained with the freshly prepared extractant was found to be lower by a factor of 4-5 as compared to the extractant aged for 15 h at +5 °C. The data obtained by the dynamic light scattering method indicate that, in freshly prepared solutions, the calix[8] arene occurs in a monomeric form, which transforms with time into large aggregates with a diameter of about 8 nm to form inverse micelles.

© Published under licence by IOP Publishing Ltd.We studied the efficiency of a facepiece filtering respirator (FFR) in presence of a measurable faceseal leakage using the previously developed model of a spherical sampler with porous layer. In our earlier study, the model was validated for a specific filter permeability value. In this follow-up study, we investigated the effect of permeability on the overall respirator performance accounting for the faceseal leakage. The Total Inward Leakage (TIL) was calculated as a function of the leakage-to-filter surface ratio and the particle diameter. A good correlation was found between the theoretical and experimental TIL values. The TIL value was shown to increase and the effect of particle size on TIL to decrease as the leakage-to- filter surface ratio grows. The model confirmed that within the most penetrating particle size range (∼50 nm) and at relatively low leakage-to-filter surface ratios, an FFR performs better (TIL is lower) when the filter has a lower permeability which should be anticipated as long as the flow through the filter represents the dominant particle penetration pathway. An increase in leak size causes the TIL to rise; furthermore, under certain leakage-to-filter surface ratios, TIL for ultrafine particles becomes essentially independent on the filter properties due to a greater contribution of the aerosol flow through the faceseal leakage. In contrast to the ultrafine fraction, the larger particles (e.g., 800 nm) entering a typical high- or medium-quality respirator filter are almost fully collected by the filter medium regardless of its permeability; at the same time, the fraction penetrated through the leakage appears to be permeability- dependent: higher permeability generally results in a lower pressure drop through the filter which increases the air flow through the filter at the expense of the leakage flow. The latter reduces the leakage effect thus improving the overall respiratory protection level. The findings of this study provide valuable information for developing new respirators with a predictable actual workplace protection factor.

© 2016, Pleiades Publishing, Inc.Previously unknown isononylcalix[8]arene was synthesized from commercially available isononylphenol. The properties of the product (solubility, extraction ability, tendency to aggregation) were compared with those of the known tert-butylcalix[8]arene. The extraction of 137Cs, 99mTc, and 241Am from alkaline carbonate solutions with solutions of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) in tetrachloroethylene was studied. The dependence of the distribution ratios on pH of the aqueous phase in the interval from 11 to 13.9 and on the nature of functional groups in the calixarene core was determined. The composition of extractable solvates of cesium and americium with calix[8]arenes was found. Calix[8]arenes extract cesium from alkaline solutions more efficiently than p-tert-butylphenol, their nonmacrocyclic analog, does. tert-Butylcalix[8]arene exhibits the highest performance, which may be due to formation of aggregates 5.7 ± 0.8 nm in diameter in the organic phase at pH 13.5 of the aqueous phase. The isononyl derivative exists in the monomeric form (particle diameter 1.9 ± 0.5 nm).

© 2016 Elsevier Ltd.Mathematical modeling of di-ethyl-hexyl-sebacate (DEHS) nanoparticle formation due to homogeneous nucleation, condensation and coagulation in a hot free turbulent jet issuing into a colder environment is performed. The Reynolds-averaged Navier-Stokes equations are used to describe the fluid flow. The aerosol dynamics is treated by transforming the general dynamic equation into moment equations which are closed by assuming a lognormal shape of the particle size distribution. The contribution of condensation and coagulation to particle formation in the case of high saturation ratios and nucleation rates is studied. The sensitivity of the model to existing approximations of the vapor saturation pressure curve and the ambient temperatures is analyzed. The influence of the main control parameters of the system, such as vapor saturation temperature and nozzle exit velocity, on the aerosol characteristics formed in the turbulent jet is investigated.

© 2016 Elsevier Ltd. All rights reserved.The problem of viscous incompressible flow past a periodic array of porous cylinders (a model of flow in an aerosol filter) is solved. The approximate periodic cell model of Kuwabara is used to formulate the fluid flow problem. The Stokes flow model is then adopted to model the flow outside the cylinder and the Darcy law of drag is applied to find the filtration velocity field inside the porous cylinder. The boundary value problems for biharmonic and Laplace equations for stream functions outside and inside the porous cylinder are solved using a boundary elements method. A good agreement of numerical and analytical models is shown. The analytical formulas for the integrals in the expressions for the stream function, vorticity and Cartesian velocity components are obtained. It is shown that the use of analytical integration gives considerable advantage in computing time.

© Taiwan Association for Aerosol Research.The penetration of aerosol particles inside a facepiece filtering respirator (FFR) was investigated using a novel model, which involved a spherical porous layer representing a filter and an annular peripheral opening representing a faceseal leakage. The model utilized a two-dimensional laminar incompressible flow in a free space and porous zones that are numerically solved by a computational fluid dynamic code FLUENT. Following the model validation, the efficiency of an FFR with an annular faceseal leakage opening was investigated as a function of the inhalation flow rate, particle size, and the ratio of the leak-to-filter areas. The filter material permeability was determined for a conventional N95 filter medium. It was found – for two inhalation flow rates (Qi = 30 and 85 L min–1) and three particle diameters (dp = 50 nm, 100 nm and 1 µm) – that once the faceseal leakage area exceeded 0.1% of the total surface of an N95 facepiece, the respirator was unable to offer the 95% protection – the minimum level that should be provided by its filter. It was demonstrated that under certain leakage condition (partially determined by the inhalation flow rate), the respirator protection level becomes independent on the particle size; furthermore, it is not anymore affected by the efficiency of its filter, and is only influenced by the size of the faceseal leakage.

© 2016, Pleiades Publishing, Ltd.The biharmonic equation formulation of the Stokes flow problem for multiquadrics method is developed. The main advantage of the approach is the iteration free method to find the solution. The numerical method is applied for the problem of steady incompressible fluid flow past a cylinder in the periodic cell of the Kuwabara model. The comparison with known analytical solution and the analysis of absolute and relative errors show that proposed approach gives satisfactory accuracy. The nonmonotonic dependence of the relative errors on the shape parameter typical for multiquadrics method is observed.

© Published under licence by IOP Publishing Ltd.Di-ethyl-hexyl-sebacate (DEHS) aerosol nanoparticle formation in a free turbulent jet as a result of nucleation, condensation and coagulation is studied using fluid flow simulation and the method of moments under the assumption of lognormal particle size distribution. The case of high nucleation rates and the coagulation-controlled growth of particles is considered. The formed aerosol performance is jet is numerically investigated for the various nozzle diameters and two approximations of the saturation pressure dependence on the temperature. It is demonstrated that a higher polydispersity of the aerosol is obtained for smaller nozzle diameters.

© Published under licence by IOP Publishing Ltd.The problem of the gas suspension flow around a porous cylinder in a periodic rectangular cell within the models of the Stokes - Darcy and the Navier-Stokes - Brinkman using the boundary element and finite volumes method was solved. Streamlines of the carrier phase flow and the air and inertia-less particles capture coefficients of at varying porosities of cylinder medium and periodic cylinder packing were compared.

© Published under licence by IOP Publishing Ltd.An approach to the calculation of flow of an incompressible viscous fluid in the Stokes approximation is developed based on the finite difference method with the use of conformal mapping. The problems of flow around a circular cylinder and ellipse in a periodic circular cell have been solved. The method is particularly well suited for solving problems of flow around bodies of an arbitrary curved shape.

© 2015 American Association for Aerosol Research. The aerosol flow through a periodic row of parallel porous cylinders is investigated. The air flow field outside the cylinders is described by the Navier-Stokes equations of viscous incompressible fluid. The extended Darcy-Brinkman equations are used to calculate the flow velocity inside a porous cylinder. The dependence of the efficiency of the deposition of aerosol particles by inertial impaction and interception on the Stokes number for various values of the Darcy number is studied. Comparison of the results obtained from the numerical model and an approximate analytical model is given. The combined approximate formula for the deposition efficiency of a cylindrical fiber in a parallel array proposed by Müller et al. (2014) is extended for the porous cylindrical fiber. The aerosol flow through the porous body composed by a random array of cylinders is calculated to estimate the interior deposition.

The results of studying a dispersed airflow around a single porous cylinder are presented. The flow field of carrying medium outside the cylinder is described within the framework of the Navier-Stokes equations for incompressible gas; inside the porous cylinder the Darcy-Brinkman extended equations for averaged velocity are used. The numerical solution of the medium equations is achieved in the FLUENT package. In the found field of carrying medium velocities the suspended particle trajectories are calculated. Also given are the dependences of the particle inertial deposition effectiveness on the Stokes number at various values of the Darcy number. © 2012 Allerton Press, Inc.

A mathematical model and numerical procedure are proposed for investigation of aspiration efficiency and the particle concentration field around a slot sampler in a moving gas. A potential-flow model for the carrier gas and a Lagrangian method for calculation of particle trajectories and concentration are employed. The particle concentration patterns around the slot and at the sampler inlet are studied. The dependence of the aspiration efficiency on the ratio of the wind and sampling velocities is analyzed. It is shown that the local aspiration efficiency calculated on the symmetry axis of the slot gives satisfactory approximation for the integral aspiration efficiency. © 2007 Elsevier Ltd. All rights reserved.

The performance of an idealized spherical sampler facing both vertically upwards and downwards in calm air is studied numerically. To describe the air flow around the sampler, both potential and viscous flow models have been adopted. The equations of particle motion are then solved to calculate the aspiration efficiency. The dependence of the aspiration efficiency upon the various parameters of importance in calm air sampling are investigated and compared where possible with the experimental work of Su and Vincent (2003, 2004a, b). It is found that in the case of upwards sampling the bluntness of the sampler only has a significant effect upon aspiration for large sampling velocities, values that would not generally be physically realistic. In the case of downwards sampling an important non-dimensional quantity, B 2RC, is identified, where B represents the sampler bluntness and RC represents the gravitational effects. This quantity determines the physical conditions for which aspiration will not occur and also the limiting values of the aspiration efficiency when aspiration does occur. In the case of low sampling velocities a difference is noted between experimental and numerical results for aspiration efficiency raising the need for more experimental data in this area. For both upwards and downwards sampling the semi-empirical models of Su and Vincent (2004b) have been modified to account for the information gained from the study. This is particularly important in the downwards sampling case where the modified model is found to agree particularly well with the results obtained. Copyright © American Association for Aerosol Research.

A mathematical model describing the unsteady thermal convection flow and deposition of growing droplets in an expansion-type Kelvin spectrometer is developed. The model includes the Navier-Stokes equations to describe the gas dynamic processes and a droplet growth model accounting for vapor depletion due to condensation. The evolution of gas temperature and velocities and growing droplet dynamics inside the spectrometer chamber are studied using CFD (computational fluid dynamics) code Fluent. The relative droplet concentrations and mass densities of condensed vapor on all droplets as a time function are investigated. In so doing it has been taking into account the droplet growth by condensation, sedimentation, heat conduction, thermal convection, droplet evaporation. It is shown that the droplet life time in the measuring chamber is limited by two processes: deposition on the walls and evaporation. The relative contribution of evaporation and sedimentation depends on the initial saturation.

Droplets moving at close distances interact hydrodynamically. We present the experimental and theoretical results of a study for monodisperse 73 μm geometric diameter droplets with initial velocities between 1.5 and 3m/s and variable generation rate (ranging from 125 to 2000s-1) emitted horizontally and vertically. During the decelerated motion the droplet Reynolds number varied between the value

The size- and time-resolved indoor/outdoor aerosol concentration relationships were studied experimentally in an empty office without internal particle sources. Two Scanning Mobility Particle Sizers (SMPS) and an Aerodynamic Particle Sizer (APS) sampled alternately from indoor and outdoor, together covering the size range 3-10,000 nm. The results showed that the indoor aerosol concentration depends mainly on the air exchange and deposition rates, and the outdoor concentration. At higher air exchange rates the indoor aerosol concentration approaches the outdoor one. This was observed for the accumulation mode particles. The size-dependent deposition rates were estimated using a simple aerosol dynamics experiment. It was based on equilibration of the indoor/outdoor concentrations by opening windows and analyzing the concentration decay curves after the windows were closed. For this purpose a simple mass balance model was used. The overall loss rate and the asymptotic value of indoor concentration were found by applying a non-linear least squares method on the time dependence of the indoor concentrations. The air exchange rate was estimated from the overall loss rate and the steady state values of the indoor/outdoor concentration of the accumulation mode particles. © Springer 2005.

Screening of a wide range of microorganisms (32 strains) isolated from various anthropogenic and natural environments and of a number of collection strains showed that the early stages of 2,4,6-trinitrotoluene (TNT) transformation by the majority of the strains studied resulted in the formation of hydroxylaminodinitrotoluenes (HADNTs). The levels of HADNTs were in a number of cases comparable to the initial TNT level. The alternative reductive attack on TNT through the reduction of the aromatic ring was not characteristic of most of the prokaryotes studied. The susceptibility to the toxic effect of TNT was different for gram-positive and gram-negative bacteria.

The performance of an idealized spherical sampler operating in calm air for an inlet arbitrarily oriented relative to the gravity force is studied theoretically. Under potential flow assumption the air velocity field is obtained by using a model of a finite-size sink on a sphere. The particle motion equations are solved to find the limiting trajectory surface and to calculate the aspiration efficiency. The singular points of the motion equations as a function of settling velocity of particles and the sampler orientation angle are investigated. The connection between the pattern of typical zones of particle trajectories around the sampler and the location of the singular points is illustrated. The effects of partial sampling from zones without particles and of particle screening are discussed. The results of parametrical investigations of the dependence of the aspiration efficiency on the Stokes number and their analysis are presented. In the case of vertically upwards orientation of the sampler the proposed mathematical model gives fair agreement with experimental data from the work by Su and Vincent (Abstracts of sixth international aerosol conference, Taipei, Taiwan, 2002a, pp. 639-640). © 2003 Elsevier Ltd. All rights reserved.

A new method of finding the limiting particle trajectory for problems of mechanics of aerosols is proposed. The method is based on formulation of the task as a boundary value problem. The deposition of the aerosol particles on a sphere in a potential flow of an incompressible fluid with regard to gravity is studied. The collection efficiency and relative area of the surface covered with particles are calculated by varying the Stokes number at different values of the relative settling velocity. Nonmonotonous behavior of the collection efficiency under changes of Stokes number is shown.