Generation of a Fine Aerosol in a Cavitation Regime
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
GENERATION OF A FINE AEROSOL IN A CAVITATION REGIME O. B. Kudryashova, E. V. Muravlev, and B. I. Vorozhtsov
UDC 621.45.042:532.592.2:544.772
Consideration is given to the problem of atomization of fine aerosols using atomizers of special designs that implement a cavitation regime. The formation of a fine aerosol is studied with the model of a pulse atomizer utilizing HEM energy and the model of an atomizer with a special nozzle to create counterflows. For these atomizers, the role of cavitation in obtaining a fine liquid aerosol is shown. A mathematical model is proposed which describes the processes of genesis of an aerosol cloud. Estimates of the critical pressure are obtained for the development of cavitation, the outflow velocity, and the resulting size of droplets as functions of the geometric parameters of the atomizers, the pressure in the structure, and the physicochemical properties of the liquid. Experimental investigations of the dispersion and concentration of aerosol particles are carried out using optical methods of measurement. Results of measuring the dispersion parameters of an aerosol in the process of cavitation atomization of liquids are presented. Keywords: cavitation, fine aerosol, pulse atomizer, arc nozzle. Introduction. In a number of practical problems, in creating an aerosol cloud, it is required that aerosols with the highest possible dispersion and specific surface of particles be obtained. This problem arises, e.g., when fire-protection conditions are created in fire-hazardous areas and in shafts. Here, a fine (microatomized) aerosol with a droplet size under ~100 μm has the advantage over powders of the same dispersion, since droplets intensely evaporate in the flame front [1]. Such aerosols may be obtained, e.g., using ultrasonic cavitation atomization [2], but the operating speed of such devices fail to meet the requirements of practical applications in many cases as in the example with fire extinguishing. Aerodynamic atomization has a theoretical limit for the size of resulting droplets as a function of the velocity of outflow of the jet [3]. But there is a possibility of obtaining a fine aerosol even at relatively small outflow velocities and expenditure of energy in atomizing. This possibility was shown by the authors in the earlier works [4, 5] with the example of a pulse generator utilizing the energy of high-energy materials (HEMs). It was shown in the works that compared to aerodynamic atomization techniques, reduction in the droplets in pulse generation is possible owing to the cavitation phenomena. In the present work, consideration is given to both a pulse generator and other designs of atomizers in which abnormally-high-amplitude oscillations of a liquid are produced in the process of operation. Such designs use special arc nozzles to create counterflows [6, 7]. The objective of the work is to theoretically and experimentally investigate the possibility of obtaining fine aerosols, and als
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