Abstract
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.
Highlights
Issues associated with finding an effective solution for Russia's food supply program that takes into account current issues of energy conservation are currently under focused consideration
The primary electrophysical properties of grain are expressed in terms of its moisture content during drying [4], along with temperature and the frequency of its external electric field
In the present paper, such variations are considered on the example of mechanically activated wheat, which represents a model of grain mass which has been bruised during drying and storage
Summary
Issues associated with finding an effective solution for Russia's food supply program that takes into account current issues of energy conservation are currently under focused consideration. The presence of an active ventilation system helps to resolve fire safety issues [6, 7] Such electrophysical indicators as electrical conductivity, permittivity and the tangent of the dielectric loss angle depend on the moisture content of grain [8]. In [9], a description of the variations in the dielectric properties of the grain medium is presented along with the observation that an increase in the dielectric constant is associated with an increase in moisture content and a decrease in frequency and that the tangent of the loss angle increases or decreases with changes in humidity and frequency. Temperature variations, explained in terms of changes in the state and amount of moisture absorbed by the grain mass, lead to a serious change in the electrophysical properties
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