Aerosol Cloud Propagation in a Closed Space

Abstract

This paper presents the results of an experimental-theoretical investigation of the evolution of a cloud of aerosol particles in a closed space obtained by the shock-wave method. It has been shown that the prevailing propagation mechanism of aerosol particles of diameter 1-7.5 μm is convective diffusion. For the considered class of aerosols, the effective value of the convective diffusion coeffi cient in a closed space has been determined.Introduction. The laws of aerosol cloud propagation in a closed space are of interest in solving many practically important problems. Among such problems are, for example, dust suppression in coal mines, fi re fi ghting in closed rooms by coolant spraying, air purifi cation and ozonization, photocatalytic neutralization of toxic gases emitted in accidents at enterprises of the chemical industry, as well as by terrorist acts with the use of toxic agents, etc. [1, 2].One effective method for generating an aerosol cloud is shock-wave spraying of a liquid by initiating a charge of a high-energy material (HEM) [3]. Unlike the known methods [4], shock-wave spraying has a number of specifi c features -a short time and a high initial fl ow velocity of the liquid, and the nonstationary and multistage character of the processes of formation and evolution of a cloud of particles.In the present paper, we present the results of the experimental-theoretical investigation and mathematical modeling of the evolution of a cloud of aerosol particles in a closed space obtained by the shock-wave method.Experimental. The shock-wave generator for spraying the liquid is schematically represented in Fig. 1. The generator consists of a case 1, a HEM charge located in the chamber 2, a vessel 3 with the sprayed liquid bounded by membranes 4, and a nozzle hole 6 in the upper cover 5 of the case. Upon initiation of a HEM charge in the chamber, a shock wave is formed and degenerates into a series of resonance acoustic waves, under the action of which cavitation of the liquid with the formation of vapor bubbles occurs. The droplet-bubble jet 7 fl ows out through the nozzle hole under the pressure created by the gaseous HEM combustion products. A primary cloud of particles is formed thereby.To measure the characteristics of the cloud of particles, we used the experimental facility schematically represented in Fig. 2.In the closed chamber 1 of size 2 × 1 × 1 m a shock-wave generator is installed. The structure of the spray cone and the concentration and dispersivity of particles of the sprayed liquid were determined with the use of contactless optical methods. Visualization of the cloud of particles was realized by the method of rapid video fi lming. The concentration and the size distribution function of particles were measured by the method of small angles of the scattering indicatrix and spectral transparency [5]. The radiation from the probing laser 3 through the mirror system 4 and optical windows 5 in the camera arrives, upon interacting with the aerosol cloud, at the radiation detectors 6 located at dista...

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