10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Modeling the Dynamics of Fractal-Like Soot Aggregates Using the Specialized Aerosol Solver
VICTOR GRYAZIN, Sergey Beresnev, Ural Federal University, Ekaterinburg, Russia
Abstract Number: 1179 Working Group: Aerosol Modeling
Abstract Various applications of processes of radiation absorption and motion of soot particles are well-known under the numerous publications. Among them appreciable interest is caused by experimental and theoretical researches of the radiometric phenomena (thermo- and photophoresis) with carbonaceous aerosols well absorbing radiation practically in the all range of radiation wavelengths. Such investigations require numerous calculations; therefore specialized aerosol solver for a wide range of calculations related to the photophoretic motion of soot particles is developed. It is useful to keep the mathematical formalism used in model of homogeneous spheres (the general solution of fractal-like particle problem is extremely difficult).
The calculation of force and velocity of longitudinal radiometric photophoresis is based on the molecular-kinetic theory of this phenomenon (Beresnev et al, 1993). For calculations of optical characteristics for fractal-like particles it is possible to use methods of effective medium approximations (e.g., Chylek et al, 1988) and theoretical predictions for fractal-like soot particles by Mackowski (2006). It was revealed that the choice m =1.764+0.570i for λ=0.68 μm (the wavelength of the He-Ne laser) is optimum. Effective thermal conductivity of fractal-like soot particles can be calculated using the method offered for estimation of thermal properties of nanofluids with significantly enhanced thermal conductivity by the aggregation of nanoparticles into clusters (Evans et al, 2008).
The determined above characteristics are used in gas-kinetic calculations for photophoretic force and velocity. Reliability and accuracy of suggested model is necessary to estimate by comparison with adequate experimental and theoretical data. The experimental results of Karasev et al (2004) on photophoretic velocities of soot particles in nitrogen provide a unique opportunity to compare results. In experiment two groups of aggregates sizes distinctly differ: small particles at Rm ≤ 0.5 μm and large particles Rm > 0.5 μm for which the mobility radius Rm was defined by various techniques at invariable fractal dimension Df =1.80.
It is obvious, that for the quantitative description of fractal-like aggregates photophoresis it is necessary to have a strict theoretical method for prediction of parameter Λ on the basis of knowledge of fractal dimension of the aggregate Df and thermal characteristics of primary particles.
The analysis has shown that for a qualitative and quantitative explanation of photophoretic motion of aggregates it is possible to apply the well-developed theory for homogeneous spherical particles at correct treatment of key parameters.
This work was supported by the Ministry of Education and Science of the Russian Federation through the base part of the State task for high educational institutions (the research project #2189).
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