Ultrasonic treatment features of liquid media and dispersed systems of various viscosities

Introduction. Dispersed systems of the “solid particles in a liquid medium” type, are widely used in mechanical engineering. They are employed in technological processes for joining metal parts, ensuring the quality of the surface layer, and applying functional and protective coatings. Regardless of the material of the dispersed particles and the matrix, the main requirement for the systems under consideration is the homogeneity of the dispersed phase particle sizes and the uniformity of their distribution within the liquid medium. In this context, ultrasonic treatment is an effective method, which, through the collapse of cavitation bubbles, allows for the dispersion of large formations or particle agglomerates while simultaneously mixing the components via acoustic flows. Despite certain achievements with individual systems, there are currently no studies aimed at establishing the relationship between the properties of the liquid medium and the dispersed phase with the parameters of the ultrasonic treatment mode, which determine the cavitation-erosion activity and the intensity of acoustic flows. The purpose of the work is to study the influence of ultrasonic treatment parameters on liquid media and dispersed systems of different viscosities, aimed at establishing the relationship between the properties of the processed medium, processing modes, cavitation-erosion activity, and the nature of acoustic flows. The paper investigates model dispersed systems with viscosities ranging from 1 to 1,395 mPa•s, obtained from glycerol-water mixtures of varying concentrations with the addition of diamond dust and graphite powder. Materials and methods. For ultrasonic treatment, a rod-type magnetostrictive oscillatory system with a VT-3 alloy emitter having a diameter of 30 mm was used. Test objects made of aluminum foil were used to determine cavitation-erosion activity. To compare the cavitation regions beneath the emitter tip and determine the initial velocity of the acoustic flow, high-speed shooting was performed at a rate of 1,212 frames/s. When studying the dynamics of flow propagation throughout the entire processed volume, shooting was used at a speed of 25 frames/s. Results and discussion. An increase in the viscosity of a liquid medium and the presence of dispersed particles in it leads to a change in the cavitation zone beneath the emitter tip, which, in turn, alters the conditions for the formation of an acoustic flow. It was found that when treating dispersed systems, the acoustic flow is formed at lower ultrasonic vibration amplitudes than in pure liquids. The initial velocities of acoustic flows for liquids and dispersed systems of different viscosities range from 0.050 to 0.565 m/s. Due to the increase in the medium's absorption capacity and the growth of energy losses to maintain cavitation, the initial velocity for dispersed systems is lower than for liquids. With an increase in the oscillation amplitude, the difference between these values grows. Patterns of erosion damage on dispersed systems are characterized by the presence of a significant area with point damage, which is a consequence of cavitation bubble collapse near dispersed phase particles distributed throughout the processed volume. The height of the cavitation-erosion activity zone ranges from 20 to 50 mm, with the largest damage area achieved at the lowest flow velocity. Thus, the processing mode must ensure a minimum flow velocity sufficient to create the force necessary to lift particles and their agglomerates from the bottom of the container, while simultaneously maintaining high cavitation-erosion activity, which limits the volume of the processed dispersed system. Studies of the acoustic flow propagation dynamics enabled the establishment of the patterns of flow movement and determination of the dependence of its velocity reduction with distance from the emitter tip.