Diffusiophoresis and Photophoresis of Heated Large Nonvolatile Aerosol Spherical Particles
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DIFFUSIOPHORESIS AND PHOTOPHORESIS OF HEATED LARGE NONVOLATILE AEROSOL SPHERICAL PARTICLES N. V. Malaia,∗ , E. R. Shchukinb ,
UDC 533.72; 532
Z. L. Shulimanovac , and D. N. Efimtsevaa
Abstract: This paper describes a theoretical study of the steady motion of a large solid nonvolatile aerosol spherical particle, which contains thermal sources within itself, in a concentration gradient of binary gas mixture components. It is assumed that an average particle surface temperature significantly differs from the temperature of the binary gas mixture surrounding it. Equations of gas dynamics are solved taking into account the power-law dependence of the molecular transfer coefficients (viscosity, thermal conductivity, and diffusion) and the density of the gaseous medium on temperature. Under boundary conditions, diffusion and thermal slip are taken into account. Numerical estimates show that the diffusion and photophoretic forces and velocity substantially depend on the average particle surface temperature. Keywords: diffusiophoresis and photophoresis, heated large nonvolatile spherical particles. DOI: 10.1134/S0021894420030141 INTRODUCTION In gaseous media, the ordered movement of aerosol particles can occur under the influence of forces of various nature (including molecular), such as diffusiophoretic and photophoretic forces. A diffusiophoretic force causes an ordered motion of particles in two- and multicomponent gaseous media with an inhomogeneous distribution of its components due to external concentration gradients. The velocity acquired by particles as the effect of a diffusiophoretic force is balanced by the force of viscous resistance of the medium is called diffusiophoretic velocity [1–3]. Photophoresis in a gas is particle motion in a field of electromagnetic radiation under the influence of radiometric force [4, 5]. When electromagnetic radiation interacts with a particle inside of it, heat energy is released with bulk density qi , which is why this particle is nonuniformly heated. The gas molecules surrounding the particle collide with its surface and then are reflected from the heated surface of the particle at a higher velocity speed than from a cold one. Depending on the size, shape, and optical properties of the particle material, as well as the radiation wavelength, both the illuminated and the shady surfaces of the particle may turn out to be hotter. Therefore, both positive (particle motion in the direction of radiation propagation) and negative (particle motion in the opposite direction) photophoresis may occur. The phenomena of diffusiophoresis and photophoresis are almost always observed in thermodynamically nonequilibrium aerodisperse systems Diffusiophoretic and photophoretic forces can have a significant impact on particle deposition in the channels of heat and mass exchangers and on particle motion in the regions of “bleaching” of dispersed systems, and they
National Research University “Belgorod State University,” Belgorod, 308007 Russia; ∗ [email protected]; [email protected]. b Joint Institute for High Tempera
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