Dynamic Study Of Liquid Absorbing Microwave

Due to the enhanced transferring, microwave heating and desorption, etc., microwave arewidely used in various fields of industrial production. However, the present researches aremainly based on experiments because of the lack of the knowledge of the interactionmechanism. The Principle of microwave heating is that liquid polar molecules rotate rapidlyunder microwave irradiation, and impact with the surrounding molecules violently to produceheat. Peak absorption frequency is an important parameter of the microwave heating, at whichthe liquid can most strongly absorb microwave energy. It has very important significance ofthe applications of Microwave in activated carbon regeneration, mass transfer enhancementand chemical synthesis. Based on dynamics, the paper studied the microscopic mechanism ofliquid molecules absorbing microwave energy and found the expression of microwave peakabsorption frequency, and thus to guide the experimental research and industrial applications.Debye relaxation theory is a basic theory about the interaction between electric field anddielectric; it regards the liquid molecules as a ball with a dipole moment, and analyzes itsdynamic behavior in the microwave field. However, it considered the short-range interactionsonly, dominated by repulsive forces between molecules, without considering long-rangeelectrostatic interactions of the dipole-dipole. We had Debye relaxation theory improved byconsidering the dipole-dipole interaction.Firstly, we substituted the Onsager effective field into kinetic equation, and the Debyerelaxation theory had been improved. The liquid molecules experience the dielectric frictioncaused by the dipole-dipole interaction besides the viscous friction.Then, we extended the complex dielectric constant to the case of rotating electric field,and found the geometrical angle between the electric displacement and the rotating electricfield equals to the phase angle the electric displacement lagging the alternating electric field.On this basis, the geometrical angle between the Onsager reaction field and the rotating dipolealso equals the phase angle the Onsager reaction field lagging the alternating dipole, thus weobtained the dielectric friction torque rotating dipole experiencing. By calculating thecoefficient of dielectric friction, we got the dielectric relaxation time formula, and then gotimproving formula of peak absorption frequency. These improving formulas were applied tothe calculation of water, ethanol and coumarins, and the results are in line with theexperimental data. The study can provide a theoretical basis of liquid absorbing microwave,as well as guide the industrial production and application.