Dielectric losses under heat treatment of dispersed media

Abstract

The purpose of the paper is to study the dependence of dielectric losses of mechanically activated grain crops on example of wheat under heat treatment on temperature and external electric field frequency as well as to examine the effect of particle size of fine grain samples on grain electrophysical characteristics and dielectric losses. Experimental samples of dispersed systems with particle sizes in the range from 50 to 1000 μm are prepared by the method of mechanical activation. The temperature dependence of the dielectric loss angle tangent is measured using the dielectric method over a wide frequency range. The dependence of the dielectric loss angle tangent tgδ of mechanically activated wheat samples with the different degrees of particle dispersion in a wide temperature range from 20°C to 250°C with a heating rate of 0.7 deg/min is studied. It is found out that the external electric field frequency varies in the range from 25 Hz to 106 Hz. Electric capacitance and conductivity are measured using an E7-20 immitance meter and a specially designed measuring cell. Dielectric characteristics are calculated. Experimental data are presented in the form of graphs and diagrams. We have determined the correlation of the tangent of the dielectric loss angle tgδ with the frequency of the external electric field and temperature, which is most characteristic for fine samples. The most finely dispersed samples with a particle size of less than 50 microns are shown to have high electrical activity. Increase in the dielectric permittivity and the tangent of the dielectric loss angle is most noticeable at the frequencies below 100 Hz. The study of dielectric characteristics allows to choose an effective energy-saving drying mode of the crop under study.