Analysis of the temperature-frequency effect on dielectric losses in a grain medium

The aim of the study is to determine the influence of the thermal effect on dielectric losses in grain mass subject to bruising during drying and storage on the example of wheat across a wide external electric field frequency range. The study of the electrophysical characteristics of a dispersed medium comprising mechanically activated wheat grains takes into account the effect of the degree of breakage on the dielectric parameters of the studied medium. The studies were carried out on experimental samples having different degrees of mechanical activation of particles, which ranged in size from from 50 to 1000 μm. Variations in the dielectric loss tangent were studied using the dielectric method across a wide temperature-frequency range. Studies of variations in dielectric properties were carried out for wheat sam-ples subjected to grinding according to the mechanical activation method at temperatures varying from 20°C to 255°C with a constant heating rate of 0.7 deg / min. During the course of the experiment, the frequency of the external electric field was varied from 25 Hz to 1∙106 Hz. Dielectric constant and dielectric loss tangent calculations were carried out using data on electrical capacity and conductivity obtained using an E7-20 immittance meter and a measuring cell in the form of a flat capacitor. An analysis of variations in these dielectric characteristics was also performed. The obtained stable correlation of the dielectric loss tangent with the frequency of external electric impact and the degree of heating of the samples was most pronounced for finely dispersed samples (particle size 50 μm). Variations in dielectric characteristics are most significant when the frequency decreases to 100 Hz and below. The study of variations in the main dielectric parameters can be used to prevent self-heating and ignition of the grain mass during storage, as well as for selecting the most efficient energy-saving drying mode.

1. Nepomniashchii E. P., Sukyasov S. V. Selection of the optimal mode of drying grain for storage in the Irkutsk region. In: Nauchnye issledovaniya studentov v reshenii aktual'nyh problem agropromyshlennogo kompleksa: materialy Vserossijskoj nauchno-prakticheskoj konferencii = Students’ scientific research in solving relevant prob-lems of the agro-industrial complex: materials of All-Russian scientific and practical conference 5–6 March 2020, Irkutsk. Vol. 3. Irkutsk: Irkutsk State Agricultural University named after A. A. Ezhevsky; 2020, р. 61-68. (In Russ.).

2. Budnikov D. A. The results of studying the energy effi-cient modes of grain drying using microwave radiation. Elektrotekhnologii i elektrooborudovanie v APK. 2020;67(1):22-27. https://doi.org/10.22314/2658-4859-2020-67-1-22-27.

3. Budnikov D. A. Improving energy efficiency of grain drying with the use of electro-physical effects. Polzunovskij al'manah. 2020;1:123-128. (In Russ.).

4. Budnikov D. A. Determination of the dielectric loss factor of a grain-air mixture. Innovacii v sel'skom hozyajstve. 2018;1:7-14. (In Russ.).

5. Panova T. V., Panov M. V. Modeling grain damage process under drying. Vestnik Bryanskoj gosudarstvennoj sel'skohozyajstvennoj akademii = Bulletin of the Bryansk State Agrarian University. 2020;6:66-71. (In Russ.).

6. Dvoenko O., Chenin A. Reducing fire hazard during grain and seeds drying and storage. Pozhary i chrezvy-chajnye situacii: predotvrashchenie, likvidaciya. 2020;3:26-32. (In Russ.).

7. Chenin A. N., Belova T. I. Increasing fire safety at grain storage and drying. In: Nauchnoe tvorchestvo studentov – razvitiyu agropromyshlennogo kompleksa: sbornik XXXIX studencheskoj nauchno-tekhnicheskoj konferencii = Sci-entific work of students –development of the agro-industrial complex: collected works of XXXIX students’ scientific and technical conference. 18 March 2020, Bry-ansk. Bryansk: Bryansk State Agrarian University; 2020, р. 97-102. (In Russ.).

8. Tsymbalova V. M., Atakhanov R. V., Lavrentiev A. A. Experimental study of cereal product dielectric permittivity. In: Innovacionnye tekhnologii v nauke i obrazovanii (IT-NO-2017): materialy V Mezhdunarodnoj nauchno-prakticheskoj konferencii = Innovative technologies in science and education (ITSE-2017): Proceedings of V anniversary international scientific and practical confer-ence. 11–15 September 2017, Divnomorskoe. Rostov-na Donu: DGTU-Print; 2017, p. 334-337. (In Russ.).

9. Nelson S. Dielectric properties of agricultural materials and their applications. London: Academic Press; 2005, 292 р.

10. Buzunova M. Y., Bonnet V. V. Mechanism of thermally stimulated current occurrence in fine heterogeneous me-dium on the example of grain crops. In: Earth and Envi-ronmental Science: IOP Conference Series. 2020;421(5). https://doi.org/10.1088/1755-1315/421/5/052032.

11. Buzunova M. Y., Bonnet V. V. Temperature condition influence analysis on the mechanoactivated wheat dielec-tric constant. Applied Physics and Cyber-Physical Sys-tems. Journal of Physics: Conference Series. 2020;1515. https://doi.org/10.1088/1742-6596/1515/2/022042.

12. Buzunova M. Yu. Investigation of dielectric structural properties of fine heterogeneous systems on the example of grain. Bajkal'skij vestnik DAAD = Baikal letter DAAD. 2019;1:124-129. (In Russ.).

13. Buzunova M. Y. Dielectric dispersion of mechanoacti-vated grain crops. Vestnik Irkutskoj gosudarstvennoj sel'skohozyajstvennoj akademii = Vestnik IrGSHA. 2019;92:25-32. (In Russ.).

14. Gorohovatskij Ju. A., Bordovskij G. A. Thermal activa-tion current spectroscopy of high-resistance semiconduc-tors and dielectrics. Moscow: Nauka; 1991, 244 p. (In Russ.).

15. Budnikov D. A., Tsymbal A. A. Dielectric properties of agricultural materials. Innovacii v sel'skom hozjajstve. 2016;3(18):154-159. (In Russ.).

16. Buzunova M. Yu., Bonnet V. V. Dielectric losses of mechanically activated grain crops during heat treatment. In: III International Scientific Conference: AGRITECH-III-2020: Agri-business, Environmental Engineering and Bio-technologies. Earth and Environmental Science: IOP Con-ference Series. 2020;548. https://doi.org/10.1088/1755-1315/548/5/052063.

17. Tsymbal A. A., Budnikov D. A. The grain dielectric properties. Vestnik Vserossijskogo nauchno-issledovatel'skogo instituta mehanizacii zhivotnovodstva = Journal of VNIIMZH. 2016;4:52-55. (In Russ.).

18. Tanaev A. B., Shcherbachenko L. A., Bezrukova Y. V., Tsydypov S. B., Buzunova M. Y., Baryshnikov D. S., et al. Peculiarities of the accumulation and transport of electret charges in fine-sized disordered structures due to internal voltage. Technical Physics. The Russian Journal of Ap-plied Physics. 2017;62(3):406-412. https://doi.org/10.1134/S1063784217030239.

19. Shourygina N. A., Scherbachenko L. A., Donskoy V. I., Karnakov V. A., Troshev A. A., Krasnov D. A. Electrical phenomena at interfaces in heterogeneous poly mineral systems dispersed. Nauchno-tekhnicheskie vedomosti Sankt-Peterburgskogo gosudarstvennogo politekhnich-eskogo universiteta. Fiziko-matematicheskie nauki = St. Petersburg Polytechnic University Journal – Physics and Mathematics. 2012;1:93-100. (In Russ.).

20. Shcherbachenko L. A., Borisov V. S., Maksimova N. T., Baryshnikov E. S., Karnakov V. A., Marchuk S. D., et al. Electret effect and electrotransport in disperse organic and in-organic systems. Technical Physics. 2009;54(9):1372-1379. https://doi.org/10.1134/S1063784209090199.