Increasing the Efficiency of Coagulation of Submicron Particles under Ultrasonic Action
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easing the Efficiency of Coagulation of Submicron Particles under Ultrasonic Action V. N. Khmeleva, A. V. Shalunova, and R. N. Golykha, * a
Biysk Technological Institute (Branch), Polzunov Altai State Technical University, Biysk, 659305 Russia *e-mail: [email protected] Received November 2, 2019; revised December 20, 2019; accepted January 13, 2020
Abstract—The results of studies into the coagulation process of submicron particles (smaller than 1–2.5 μm) under various conditions of ultrasonic exposure are presented to identify the possibility of increasing the efficiency of coagulation. An analysis of the peculiarities of the coagulation process both with a sinusoidal effect and with shock-wave (pulsed) action has made it possible to establish that the shock-wave action provides a coagulation rate of submicron particles that is up to 20 times higher when compared with the sinusoidal effect at the same total energy of exposure. It is shown that the cause of the acceleration of the process is nonlinear effects arising from shock-wave action and affecting the coagulation rate of particles (a change in the crosssectional area of collision, local medium compaction, and mutual diffusion of the gas surrounding the particle during the transitional flow regime between the free and continuous molecules). Keywords: ultrasound, shock wave, coagulation, submicron particles, speed, Smoluchowski equation, nonlinear effects DOI: 10.1134/S0040579520030069
INTRODUCTION Aerosols that form in the atmosphere due to human impact, industrial accidents, terrorist acts, and natural processes are a global problem. Mankind is continuously forced to fight with fogs, smog, dust, and aerosols of harmful, toxic, and radioactive substances [1–4]. The most dangerous are aerosols of fine particles (smaller than 1–2.5 μm). Such particles have a high total surface (more than 55% of the total surface of the particles emitted into the atmosphere) and a countable concentration (more than 95% of the total counted concentration, even with a small mass fraction (less than 1% of the total fraction of aerosols contained in the atmosphere)). Due to their small size and mass, such aerosols can be held in the air for a long time and can easily penetrate the alveoli of the human lung, causing irreversible changes in the body. Today, one of the most effective methods for capturing aerosol particles moving through gas ducts and penetrating into the atmosphere is to precombine particles into agglomerates (coagulation) under the influence of high-intensity sinusoidal ultrasonic vibrations for the further capture of aggregated particles by traditional methods (inertial or gravitational deposition, filtration through porous material, etc.). To date, the effectiveness of ultrasonic coagulation has been repeatedly proven for particles larger than 2.5 μm. Many authors indicate coagulation modes
[2–5] at which the greatest degree of enlargement is achieved, and special equipment [3–11] is proposed that allows particles to be coagulated both in open space and in a closed
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