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Introduction to uniformity of Microwave heating

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Microwave heating uses the principle of dielectric loss, adopts the way of integral heating, directly heats the material through molecular polarization and ionic conduction effects. It has the characteristics of rapid heating and high thermal efficiency. It is used in food processing, biopharmaceutical, and so on. Petrochemical, metallurgy and other energy consumption areas have significant advantages.

For example, in the synthesis experiment of microwave assisted heating, rapid microwave heating can increase the overall reaction rate. At the same time, the temperature distribution may be different in the process of microwave heating. The part with large dielectric loss in the component will be preferentially heated by microwave, resulting in the star-filled effect, which will lead to the whole reaction system being heated by microwave.

This paper introduces the factors influencing the temperature distribution of heated materials during microwave heating.


The Electric characteristics of Microwave heating and its influence factors


During microwave heating, there are obvious electrical properties, such as conductivity, permittivity, permeability and so on, which are nonlinear functions of temperature, which have an effect on the uniformity of material heating.

The electric field intensity in the resonator is controlled by the input power, and its distribution is related to the size of the cavity, the shape and size of the material, the position of the material, etc. Under different electric field distribution, the uniform distribution of the material temperature will change.

In addition, there are other factors, which will affect the interaction between material composition and microwave energy, and produce its unique effect on microwave heating.


Microwave heating model-heat transfer equation


There have been many achievements in microwave heating model, such as Knoerzer et al., in the process of microwave heating of materials, the heat transfer equation has been established by neglecting water loss.



According to the heat transfer equation, there are many factors that affect the uniformity of microwave heating, including:
dielectric properties (dielectric constant and dielectric loss factor);
Thermal properties (specific heat capacity and thermal conductivity);
Parameters of resonator (microwave power, cavity size, number of feed ru ports, etc.);
Physical properties of heated materials (size, shape, density, location, etc.).


Significance of understanding uniformity of Microwave heating


The significance of understanding the uniformity of microwave heating lies in that when microwave heating is adopted, the advantages and disadvantages of the method can be evaluated quickly by using the homogeneity model, and the uniform distribution of materials heated can be analyzed to improve the heating efficiency.