Modeling of the heat mode of the independent environment for microwave heating
DOI:
https://doi.org/10.31548/energiya2018.03.049Abstract
The use of ultra-high-frequency electromagnetic field for heating food and agricultural materials - microwave heating is widely used in modern technologies of agro-industrial production. The basis of the application of the microwave field is the volume (uniform in volume) heating of the material, the selectivity of the intensity of the energy supply, the high speed of heating and the insignificant duration of the transition process, can use it as an intensifying action, typical mass transfer processes. It is quite effective to use the microwave field (MHP) for intensification, the most non-waste method of oil extraction - extraction of useful oil substances from plant raw materials into a liquid extractant. Since the traditional method of thermostating the liquid extractant is energy intensive and inertial, in the management plan, the principle of selective heating of the system is used: "solid phase - liquid". To determine the dynamic parameters of the heating of such a system in the electromagnetic field of microwave, it is necessary to have a mathematical description of the non-stationary temperature change of the two fractions, which is used to evaluate the conditions for the optimal mode of heat and mass transfer in the extraction process.
The efficiency of the use of the electromagnetic field energy for the intensification of extraction processes is theoretically proved and experimentally confirmed in the fundamental works [1, 2]. Possibility of intensification of extraction processes in the production of soybean oil, rape and others. raw materials are proved and quantified in works [3-6]. Thermal regimes for selective microwave heating of dielectrics are considered in [7-9]. In work [8] different modes of determining the value of overheating of the solid phase relative to the medium are analyzed. In [7], the calculation of the thermal field of the solid inclusion and the medium under the boundary conditions of the fourth kind (contact heat exchange) is given. However, for the analysis and development of energy-efficient extraction of oil materials, it is necessary to have an analytical dependence of temperature and temperature changes of the solid and liquid phases in time, depending on the initial parameters of the process.
Determination of the dynamics of the heating process of a two-component (solid-liquid phase) medium in the electromagnetic field of microwave.
To determine the dynamic characteristics of objects of modeling and subsequent automation, the analytical method of calculation is used: on the basis of the existing information [2] on the physical picture of the phenomena occurring on the interaction of the disperse material (shrot) with the liquid medium in the electric field of the microwave, the thermal equation in the differential form with subsequent simplifying (commonly accepted [3, 8]) assumptions. We consider that dielectrics represent a fine-dispersed system consisting of two phases: solid (with a mark of 1) and liquid (with a mark of 2). The first one is called the inclusion, and the second medium. Both phases are in a closed volume, which through the enclosure (housing) with the surface interacts with the surrounding environment (external air). The power (heat) emitted per unit volume is determined by the formula [8] (1).
The process of heat transfer is considered in the apparatus of periodic action, which is presented as a device of perfect mixing. The heating of the inclusion (regardless of the shape of particles) is non-gradient.
In fig. 1 shows the graphic dependences (built on the above formulas (11) and (12)) of changes in the temperature of the liquid medium (Fig. 1a), solid inclusion (Fig. 1b).
To determine the transfer functions of the installation for heating (and adjacent operations) of nonhomogeneous media in the microwave field, we give the equations (7) and (8) to the canonical form (by dividing all the members of the equations by the coefficient and using the Laplace transform at zero initial conditions, we obtain the equation in the operator form (8) - (9).
The block diagram of the control object is shown in Fig. 2
Conclusions
1. The mathematical models obtained and the calculated analytical dependencies allow to determine the dynamics of heating (the heating time to the given and the final temperature), depending on the parameters of the electromagnetic field and the properties of the material.
2. The block diagram and transfer functions allow to choose, synthesize the system of automatic control of temperature mode.
References
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