A method of identification of maximum size and concentration of submicron aerosol particles based on measurement of intensity attenuation of a parallel beam of probe optical radiation is described. Offered method makes it possible to determine both particle concentration and maximum particle size with controlled accuracy for aerosol media without any initial information about particle size distribution

Arkhipov, Vladimir A.

Bondarchuk, Ivan S.

Zhukov, Alexander S.

English

Tomsk State University Repository

  IDENTIFICATION OF SIZE AND CONCENTRATION OF SUBMICRON PARTICLES ON THE BASIS OF RAYLEIGH SCATTERING MODEL Ivan. S. Bondarchuk1, *, Vladimir A. Arkhipov1, and Alexander S. Zhukov1 1National Research Tomsk State University, 634050 Tomsk, Russia Abstract. A method of identification of maximum size and concentration of submicron aerosol particles based on measurement of intensity attenuation of a parallel beam of probe optical radiation is described. Offered method makes it possible to determine both particle concentration and maximum particle size with controlled accuracy for aerosol media without any initial information about particle size distribution. Particle size distribution of aerosol media (in the process of plasma chemical synthesis, preparation of fuel mixtures, analysis of combustion products etc.) laws of formation and its mass-geometry characteristics determine parameters and efficiency of many technology processes [1]. In this case the most accurate methods of study of such objects are non-contact optical methods. An approach making it possible to identify mass concentration and maximum size of condensed particles using the data of laser probing of aerosol formations is presented in this paper. According to offered method of measurement of optical density of dispersed medium measurements are performed in several points of spectral wavelength range: the boundaries of this range are selected on the basis of information about complex refractive index of particle material. When monochromatic radiation with the wavelength λ passes through a layer with the width l of uniformly distributed particles with the diameter D and mass concentration Cm its intensity is attenuated due to scattering and absorption by particles. Spectral transmittance Tλ, associated with Beer–Lambert–Bouguer law [2] is a quantitative characteristic of attenuation.  0 exp τ     T I I         (1) where Iλ – radiation flux passed through the layer; I0λ – incident radiation flux. Expression for spectral optical density τλ for monodisperse particles in the framework of assumptions of Mie theory has the following form [2]:  1.5,  	mC lQ mD        (2)                                                  * Corresponding author: ivanich_91@mail.ru      DOI: 10.1051/01014 (2016),  2016-72 7201014HMTTSCMATEC Web of Conferences matecconf/2016 © The Authors,  published  by EDP Sciences.  This  is  an  open  access  article  distributed  under  the  terms  of  the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). where ρ – particle material density; Dependence Q(α,m) of dimensionless attenuation efficiency factor in equation (2) has a complex oscillatory character on diffraction parameter (Mie parameter) α=(πD)/γ, from complex refractive index of particle material m=n-i χ (n – refractive index; χ – attenuation coefficient) and in common case is calculated using exact formulae of Mie theory.In case of “small” particles if Rayleigh scattering condition is met α < 0.2 attenuation efficiency factor is determined from the following analytical dependence [2]:    ,  Q m F m , where     2 22 2242 2    nF mn n    (3) After substitution of (3) into the expression for optical density (2) we have the following:    calc 1.5 1.5      	  	m mC l C lDF m F mD     (4) (4) implies that spectral density τλ in case of Rayleigh scattering does not depend on particle size D. Therefore, mass particle concentration can be determined from (4) using value of τλ:  1.5	 mCl F m         (5) In case of polydisperse particles, the expression for spectral optical density is determined as [2, 3]:     2020,1.5  	mQ m D f D dDC lD f D dD       (6) It should be noted that substitution of expression (3) for Q(α,m) in (6) as in case of Rayleigh scattering gives the same expression as (5) for mass concentration of particles.  Fig. 1. Caption of the figure 1. Below the figure. This method of Cm calculation from formula (5) using measured value of τλ is considered valid only for a limited range of probe radiation wavelength λ ≥ λ*.    DOI: 10.1051/01014 (2016),  2016-72 7201014HMTTSCMATEC Web of Conferences matecconf/20162To determine wavelength λ*, limiting Rayleigh scattering region spectral optical density meas  is measured in a certain wavelength min max      range and from the analysis of function meas calc      limiting value λ* is determined. Up to this value   decreases monotonically (fig.1) and then *const     for λ > λ*. Particle mass concentration for region λ > λ* is determined using formula (5).In order to calculate Dmax value using relation given in [2]  *max * *  D        (7) we need an algorithm of identification of boundary value of diffraction  parameter α*.Analysis of dependencies Q(α) (fig. 2) shows that α* value limiting Rayleigh scattering region is determined by wavelength λ.Calculated dependencies (for soot) are given in fig. 3. These charts were built on the basis of condition of 5 % and 10 % deviation Q(α) of Rayleigh approximation from the exact Mie theory solution. Thus, there are certain values α* = f(λ) for each wavelength which make Rayleigh approximation valid for α < α* with specified controlled accuracy. These dependences are well approximated by the following function  exp    a b         (8) where [λ] = μm, and constants а and b depend on optical constants of material of studied particles. The following expression for mD  can be obtained from (7) and (8): * exp( )   mD a b .Fig. 2. Exact and approximated dependence of attenuation efficiency factor on diffraction parameter.     DOI: 10.1051/01014 (2016),  2016-72 7201014HMTTSCMATEC Web of Conferences matecconf/20163Fig. 3. α* = f(λ) dependence for soot.For λ = (1÷6) μm dependence of refractive index n and attenuation coefficient χ on wavelength λ is as follows n=1.6-0.3 λ, χ = 0.6 λ [2]; approximation error comprises (2.5÷3.0) %. Final expression for maximum particle size Dm for strictly determined dependence * 0.217 exp( 0.155 )      is as follows: *0.217 exp( 0.155 )   mD      (9)Thus, the offered method makes it possible to determine both particle concentration and maximum particle size with controlled accuracy for aerosol media without any initial information about particle size distribution. Acknowledgments This research was supported by the Ministry of Education and Science of the Russian Federation under the Federal Target Program “Research and development on priority directions of scientific-technological complex of Russia for 2014-2020”, the agreement No. 14.578.21.0034, unique identifier PNI RFMEFI57814X0034. References 1. I.S. Bondarchuk, I.A. Zhukov, B.V. Borisov, MATEC Web Conf. 23, 01046 (2015)2. V.A. Arkhipov, S.S. Bondarchuk, Optical diagnostic methods of heterogeneous plasma combustion products: Study guide (Tomsk State University, Tomsk, 2012) [in Russian]3. V.A. Arkhipov, S.S. Bondarchuk, N.G. Kvesko, A.T. Roslyak, V.F. Trofimov, Atmos. Oceanic Opt. 17 (2004)     DOI: 10.1051/01014 (2016),  2016-72 7201014HMTTSCMATEC Web of Conferences matecconf/20164

Identification of size and concentration of submicron particles on the basis of rayleigh scattering model

Ivan. S. Bondarchuk

Vladimir A. Arkhipov

Alexander S. Zhukov

EDP Sciences OAI-PMH repository (1.2.0)

Identification of Size and Concentration of Submicron Particles on the Basis of Rayleigh Scattering Model

http://vital.lib.tsu.ru/vital/access/services/Download/vtls:000623974/SOURCE1

Identification of size and concentration of submicron particles on the basis of rayleigh scattering model

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