Principle of Microwave Drying
Microwave is an electromagnetic wave with extremely short wavelength, the wavelength is between 1mm and 1m, and its corresponding frequency is between 300GHz and 300MHz. In order to prevent the interference of microwaves to radio communication, broadcasting and radar, the international regulations for microwave heating and microwave drying have four frequency sections, namely: L section, the frequency is 890~940MHz, and the center wavelength is 330mm; S section, the frequency is 2400~2500MHz, the central wavelength is 122mm; C section, the frequency is 5725~5875MHz, the central wavelength is 52mm; K section, the frequency is 22000~22250MHz, the central wavelength is 8mm. Only the L and S sections are used in domestic microwave ovens. Microwaves are obtained by applying direct current or 50Hz alternating current to electric vacuum devices or semiconductor devices, and using electrons to make special movements in a magnetic field. This motion can be explained simply as follows: From the perspective of the electrical structure of the medium, one type of molecule is called a non-polar molecular dielectric, and the other is called a polar molecular dielectric. In general, they are arranged randomly, if they are placed in an alternating electric field, the polar molecular orientation of these media also changes with the polarity of the electric field, which is called polarization. The stronger the applied electric field, the stronger the polarization, the faster the polarity of the applied electric field changes, the faster the polarization, and the more intense the thermal motion of molecules and the friction between adjacent molecules. In this process, the conversion of electromagnetic energy to heat energy is completed. When the heated material is placed in the microwave field, its polar molecules oscillate and rub back and forth with the microwave frequency at a high frequency of billions of times per second, generating heat It is enough to make the material achieve the purpose of heat drying in a very short time.
The mechanism of microwave sterilization
Microwave sterilization is the result of the combined effect of thermal and biological effects of electromagnetic fields. The thermal effect of microwave on bacteria is to denature the protein, so that the bacteria lose the conditions for nutrition, reproduction and survival and die. The biological effect of microwave on bacteria is that the microwave electric field changes the permeability of the cell membrane section. Therefore, the bacteria are malnourished and cannot metabolize normally. In addition, the nucleic acid (RNA) and deoxyribonucleic acid (DNA), which determine the normal growth and stable genetic reproduction of bacteria, are caused by several hydrogen bond relaxation, breakage and recombination, thereby inducing genetic mutation, or chromosomal aberration or even breakage.
Main features of microwave heating
1. Rapid heating
The heating of Microwave Drying Equipment is completely different from the traditional heating method. It is the process of making the heated material itself a heating body without heat conduction. Therefore, the heating temperature can be reached in a very short time despite the material with poor thermal conductivity.
2. Heating evenly
Regardless of the shape of each part of the object, microwave heating can make the surface of the object evenly penetrate the electromagnetic wave and generate heat energy. Therefore, the heating uniformity is good, and the phenomenon of external coke endogenous will not occur.
3. Energy saving and high efficiency
Since the substance containing moisture easily absorbs microwaves and generates heat, there is almost no other loss except a small amount of transmission loss. Therefore, it has high thermal efficiency and energy saving. It saves more than 1/3 energy than infrared heating.
4. Anti-mildew, sterilization and preservation
Microwave heating has thermal and biological effects, and can sterilize and prevent mildew at lower temperatures. Due to the fast heating speed and short time, the activity of the material and the vitamins, original colors and nutrients in the food can be preserved to the greatest extent.
5. Advanced technology
Immediate heating and termination can be achieved as long as the microwave power is controlled. The application of man-machine interface and PLC can carry out the programmable automation control of heating process and heating process specification.
6. Safe and harmless
Because the microwave energy is controlled to work in the heating chamber and waveguide made of metal, there is very little microwave leakage, no radiation hazards and no harmful gas emissions, no waste heat and dust pollution, neither food pollution nor environmental pollution.
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