In the final of the startup competition at the XI Festival of Innovative Projects "Sikorsky Challenge 2022", a project on the production of hydrogen by electrolysis using ultrasonic cavitation was presented. In a conversation with one of the participants in this project - PhD in Engineering, Associate Professor of the School of MMI, winner of the Presidential Prize for Young Scientists 2021 Andriy Zilinsky - a KP correspondent learned about the achievements of a group of KPI scientists working on the introduction of ultrasonic cavitation technologies and related technological equipment into production.

- Andriy Ivanovych, tell us about the history of this project.

- There are several research groups at the Department of Applied Hydroaeromechanics and Mechanotronics of the MMI. In cooperation with scientists from the research group "Ultrasonic Cavitation Technologies and Equipment for their Implementation" (supervisor - Doctor of Technical Sciences, Professor Oleksandr Luhovskyi) and colleagues from the research group "Hydromechanical Processes in Viscous and Abnormally Viscous Liquids in Closed and Open Tanks of Machines and Apparatus" (supervisor - Doctor of Technical Sciences, Professor Oleg Yakhno), a project was created under the guidance of Candidate of Technical Sciences, Associate Professor Igor Nochnichenko. We have developed and investigated mechanotronic equipment for the implementation of electrolytic hydrogen production technology under ultrasonic cavitation.

- Which of these research groups do you belong to?

- To the research group headed by Oleksandr Luhovskyi. It develops ultrasonic processing equipment for the treatment of liquid media, as well as technologies for ultrasonic reagent-free disinfection of liquids, ultrasonic fine spraying of liquids as part of mechanotronic irrigation systems and artificial microclimate, ultrasonic spraying of molten metals to obtain fine metal powders, ultrasonic cavitation filtration of liquids, preparation of stable emulsions by ultrasonic cavitation mixing at the molecular level, ultrasonic

- What is the goal of your research? I would like to understand the nature of the problem more thoroughly.

- Ultrasonic cavitation treatment of liquid media is widely used in various industries. We are talking about technological processes related to the mixing and dispersing of liquids and solids. The result is the production of direct and reverse emulsions, separation of liquid heterogeneous mixtures, flotation (a method of separating some minerals from others in an aqueous medium - ed.). Cavitation impact allows changing the rate of diffusion, oxidation, crystallization and dissolution of substances, promotes the activation of chemical reactions and many other physical processes. This helps to intensify technological processes.

The introduction of acoustic vibrations into a liquid with an intensity exceeding the threshold of cavitation under these conditions leads to the nucleation, pulsation and slamming of vapor-gas cavitation bubbles. Acoustic microcurrents, powerful shock waves and cumulative jets are formed, which intensively destroy hard surfaces. It is acoustic microcurrents that provide high-quality removal of grease films from product surfaces and mix liquid components at the molecular level. The high pressure and temperature that occur in micro-volumes when cavitation vapor-gas bubbles are slammed create conditions for the emergence of electric charges, energy-rich dissociated and ionized molecules, as well as atoms and free radicals. This phenomenon leads to the activation of the liquid. Shock waves, pressure, high temperatures and the intensification of chemical processes accompanying ultrasonic cavitation provide the effect of disinfecting liquids and surfaces.

- Who worked on this problem?

- Many young scientists have defended their theses under the supervision of Oleksandr Luhovskyi. Among them are Ihor Anatoliiovych Hryshko, PhD in Engineering, Associate Professor, Director of the Institute of MMI, who received the Presidential Award for Young Scientists in 2014 for developing the technology of using ultrasound to disinfect liquids; Andrii Valeriiovych Movchaniuk and Alina Viktorivna Shulga, Associate Professors of the Faculty of Radio Engineering. I also defended my PhD thesis under the supervision of Oleksandr Fedorovych.

By the way, Professor Luhovskyi was awarded the Borys Paton National Prize of Ukraine in 2021 for his scientific research. Thus, we are talking about the success of the research team in the materials science, engineering, and acoustic fields.

- It would be interesting to learn a little more about the phenomenon of cavitation.

- It was first discovered by the academician Leonard Euler (1707-1783). The scientist, who had never observed the phenomenon of cavitation in practice, was able to theoretically substantiate the possibility of ruptures in a liquid due to a local pressure drop with subsequent slamming of the resulting voids. Subsequently, numerous experimental and theoretical studies have shown that the formation of cavitation bubbles-cavities in a liquid occurs when the pressure drops locally below a certain critical value, which corresponds to the cavitation threshold. Typically, the critical value corresponds to a pressure slightly lower than the pressure of saturated vapor at a given temperature. Cavitation bubbles filled with steam, gas, or a mixture of both, when they enter the area of high pressure, abruptly collapse, and this is accompanied by the occurrence of pressure shocks reaching 1000 MPa, a temperature increase of up to 1000 oC, and electrical discharges.

Depending on the method of reducing the pressure in the liquid, a distinction is made between hydrodynamic cavitation, which occurs due to high local velocities in a droplet flow of liquid, and ultrasonic cavitation, which occurs due to the passage of a sound wave with high intensity.

- What is the principle of ultrasonic disinfection technology?

- Ultrasonic waves create high-frequency vibrations in the liquid, which lead to the formation of cavitation bubbles under certain conditions. During this process, high temperature and pressure occur, and oxidation processes take place. All this leads to the destruction of microorganisms. We are talking about large-sized microorganisms, bacteria, viruses and fungi.

Ultrasonic sterilization can be used to disinfect and sterilize a variety of items: surgical instruments, dental instruments, dentures, medical devices, glassware and other items that are used under sterile conditions. Furthermore, ultrasonic sterilization can be used to purify water and liquids from microorganisms. What is important is that this method does not use chemicals and is suitable for the treatment of liquids of different transparency, and is therefore environmentally safe.

- From our conversation, it is clear that the use of high-power ultrasonic vibrations and the cavitation phenomena that accompany them during liquid filtration not only intensifies this process and improves its quality, but also helps to ensure the self-regeneration of the filter element. What other advantages are worth mentioning?

- The development of maintenance-free filters is an important trend in the development of filter technology. The use of ultrasonic vibrations with a frequency of 20-100 kHz in liquid filtration technology provides special opportunities. The use of ultrasonic energy in the process of liquid filtration makes it possible to significantly simplify the design and reduce the size of such filters. This is due to the elimination of circulation pumps or drives for the rotation of filter drums, which ensure the achievement of the required difference in the relative velocities of the pollutant and the clean liquid, as well as low-frequency vibration drives. The latter ensure periodic or continuous discharge of sediment from the filter baffle. The rejection of bulky and energy-consuming auxiliary units in maintenance-free filters by using the capabilities of ultrasonic transducers allows expanding the range of sizes of this class of filters - from stationary large-sized industrial applications to low-cost autonomous wide-area applications. The main advantages of such filters are that they are maintenance-free and have an almost unlimited service life. They also have a four- to fivefold higher degree of filtration with the same performance and porosity of the filter membrane. The latter are also preserved in filters with ultrasonic transducers (such filters are usually called ultrasonic).

- We're talking about a research team, but we haven't met all of our colleagues yet. Could you please introduce them?

- With pleasure. Alina Viktorovna Shulga, PhD in Engineering, Associate Professor at RTF, works on the development and implementation of spray nozzles based on ultrasonic effects. Ultrasonic atomization in a thin liquid layer is widely used in the pharmaceutical, food, cosmetic and other industrial sectors. This method allows to produce liquid monodisperse aerosols with droplet sizes in the range of 5 to 20µm.

A significant contribution was made by Iryna Bernyk, Doctor of Technical Sciences, who is currently the head of the department at Vinnytsia National Agrarian University. She defended her PhD and doctoral dissertations under the scientific supervision of Professor O.F. Lugovskyi. Her doctoral dissertation was devoted to the development of ultrasonic cavitation technology for the extraction of pectin (a water-soluble substance contained in the cell juice of fruits and vegetables - ed.) from plant material and the creation of equipment for its implementation. The principle of ultrasonic technology for the production of pectin is to use the sound-capillary effect to remove useful components from plant material.

The next one is Andrii Movchaniuk, PhD, associate professor at the RTF. He studied the technology and equipment for vibration-impact hardening of surfaces and stress relief from welded joints, which is used to relieve stresses that occur in metal parts after welding. This increases the strength and service life of the parts. Ultrasonic vibration-impact stress relief (as this technology is called) can be applied to various types of metals, including steels, aluminum alloys and titanium, as well as to metal parts of various shapes and sizes, including welds, plates and pipes.

The interview was conducted by Viktor Zadvornov