Time Characteristics of Initial Stages for Aerosols Diffusion in Channels of Ventilation Systems

The processes of aerosols diffusion for turbulent flows in channels of industrial ventilation systems are considered. To describe the motion of discrete spherical particle in homogeneous turbulent flow, we apply the Basset equation. To analyze the characteristics of the turbulent flow, the time Lagrange correlation coefficients and the Lagrange functions of the energy spectrum are used. The time correlation coefficient of the main flow is approximated by the exponential dependence. The process of aerosols diffusion is conditionally divided into three stages: induction, transition and basic. In the induction period, the particles are accelerated by the Stokes forces from zero velocity to the main flow velocity, while the diffusion process is practically absent. In the transition period, the diffusion process occurs at variable diffusion coefficient. After the initial stages, the basic diffusion process of aerosol particles begins at constant diffusion coefficient, which can be investigated by known methods. The time characteristics of the initial periods in aerosols diffusion were estimated. The approximate expression was obtained for the diffusion coefficient of aerosol particles in the transition period. It is recommended when placing the concentration control means both the length of the concentration equalization path and the distance traveled by the particles during the induction and transient periods should be considered. When the length of the ventilation channel is relatively small, or the concentration control means are installed at sufficiently small distance from the source of emissions, the results of the control should be corrected.