Michal Rajňák: Nanomaterials are the most effective way to more efficient cooling of electrical machines

Michal Rajňák, former student of the Faculty of Humanities and Natural Sciences at  University of Prešov, had made good and bad decision during his studies; by the end of the compulsory pedagogical practice he decided not to become a teacher due to the very small interest of students in physics. It is definitely bad for primary and secondary education schools because he certainly has the talent to clearly explain the secrets of physics to students. Yet the decision was very good for the science which he preferred. The greatest evidence is the recent 2019 SAS Award for the results of the research work of the young scientists which he was rewarded already as an independent researcher at the Institute of Experimental Physics of the Slovak Academy of Sciences in Košice for significant results in the field of ferromagnetic fluids for applications in electrical engineering.

“At the University of Prešov, I felt best in the laboratories which, thanks to Professor Marián Reiffers, my thesis supervisor, were equipped with top experimental equipment in the field of condensed matter physics” says Dr. Michal Rajňák about the early part of his life journey. Prof. Marián Reiffers, who has been associated with the Institute of Experimental Physics of the Slovak Academy of Sciences in Košice since 1980, directed the young physicist to the topic of his PhD. thesis in the field of magnetic fluids under the supervision of Dr. Milan Timko within the scientific group of assoc. prof. Peter Kopčanský. Here, as doctoral student at the P. J. Šafárik University in Košice, he participated in the experimental research of magneto-dielectric properties of ferromagnetic fluids based on transformer oils.

“During the last year of my doctoral study (in 2015), our team managed to detect interesting reversible structural changes in a ferromagnetic fluid under the influence of an electric field. So far the scientific attention has been given mainly to the intuitive structuring of magnetic fluids in a magnetic field, and therefore we decided to deal more intensively with the structure and dynamics of ferromagnetic fluids in the electric field. Our recent experimental results suggest that polarized clusters of magnetic nanoparticles impact the distribution of the electric field in a magnetic fluid and may serve as pinning centers for free electric charge. It is possible that this is why the ferromagnetic fluid can withstand higher electrical voltages than pure transformer oil,” said Michal Rajňák, who has been focusing his scientific research on magnetic fluids for applications in electrical engineering since 2018. Demands for the power systems are rising and scientists are expected to bring new solutions to improve cooling mediums and increase their efficiency. It turns out that nanomaterials are one of the most promising ways: “On the other hand, the structuring of a ferromagnetic fluid in an electric field opens up new possibilities for research and potential applications. As we suggested in our recent work (Phys. Rev. Applied 11, 024032), phenomena related to electrically controlled structuring of magnetic fluids can find use in the field of sensory applications, switching and possibly nanorobotics,” adds Michal Rajňák.

The young scientist is involved in several research projects. He is currently leading two national research projects. Within the scope of the APVV project for applied research NANOELEN – Nanofluids in electrical engineering (2019 – 2023), he is working as the project coordinator on the research, development and application of alternative ferromagnetic nanofluids for cooling and electrical insulation of electrical transformers. He is experimentally investigating the dielectric, magnetic and thermal properties of ferromagnetic nanofluids based on the contemporary transformer oils. The research is done in cooperation with the Technical University in Košice and with the industrial partner Elektrotechnický výskumný a projektový ústav (“Electrotechnical research and projecting company”) in Nová Dubnica, which tests the investigated nanofluids in model transformers under various load regimes. His second project Structure and Dynamics of Magnetic Fluids in an Electric Field (2/0011/20, 2020 – 2023) by VEGA focuses on basic research of structure and dynamics of ferromagnetic nanofluids in an external electric field. He is looking for a way to describe the unclear mechanism of conductive streamer development in ferromagnetic nanofluids. In addition to this research he also investigates structuring phenomenas in ferromagnetic nanofluids at the macro- and nano-level. He publishes his scientific results in peer-reviewed scientific journals. At the age of 33, he is the first author of seventeen publications and already has seventy entries in the list of co-authored publications.

Among other various awards, let us mention last year’s first place in the competition of young scientists of SAS under 35 years of age within the 1st Department of Life Sciences for his work “Magnetic Fluids for Applications in Electrical Engineering”. In 2017, he won the Young Physicists Competition, organized by the Slovak Physical Society.

Michal Rajňák develops his expertise based on his knowledge of electrical engineering, for which he is grateful to his grandfather. He spent many moments on his farm in Vyšný Hrušov during his childhood. He is also grateful for the love of nature: “My wife and I live in Prešov, I commute to Košice by train which, by the way, I like very much, but my heart beats for relax in nature and work around the house. I try to travel to my heritage at least once or twice a week where I have started beekeeping. I chose the scientific approach; first I completed a course and studied literature,” adds Michal Rajňák with a smile.

Although the coronavirus pandemic has limited his intentions to travel to international short-term internships and conferences (such as The 11th Conference on Broadband Dielectric Spectroscopy and its Applications in Spain), he praises that he was able to finish articles and process measured data. What will he focus on in the near future? “Until the end of the year, I will be doing measurements for colleagues on a vibrating magnetometer and write an article about the structure of the ferromagnetic fluid under the simultaneous influence of the electric and magnetic field. In addition, me and my colleagues, as well as engineering and doctoral students, are trying to experimentally determine whether there is an electromagnetic bond in magnetic fluids. We want to find out whether, in addition to the geometric structure, it is possible to induce magnetic interactions by electric forces between magnetic nanoparticles, which under normal conditions do not interact magnetically. We believe that finding answers to questions about electromagnetic coupling or the mechanism of electrical jump in ferromagnetic fluids will help to remove some of the barriers that hinder the technological transfer of ferromagnetic fluids to the electrical engineering industry,” said Michal Rajňák.

Original author and photo: Katarína Čižmáriková
Original text: News at SAS (published on September 4, 2020)