Microwave drying characteristics

Microwave is a kind of electromagnetic wave with very short wavelength ranging from 1 m m to 1 m and corresponding frequency ranging from 300 GHz to 300 MHz. In order to prevent the interference of microwave to radio communication, broadcasting and radar, there are four frequencies for microwave heating and microwave drying, which are L-band, frequency 890-940 MHz, central wavelength 0.330 m; S-band, frequency 2400-2500 MHz, central wavelength 0.122 m; C-band, frequency 5725-5875 MHz, central wavelength 0.052 m; K-band, frequency 2200-22250MHz, central wavelength. The wavelength is 0.008m. Only L and S segments are used in domestic microwave ovens. Microwave is obtained by the special movement of electrons in the magnetic field through DC or 50Hz alternating current on the electro-vacuum devices or semiconductor devices. This motion can be explained simply as follows: from the point of view of dielectric structure, one kind of molecule is called electrodeless molecular dielectrics, the other is called polar molecular dielectrics. In general, they are arranged irregularly. If they are placed in an alternating electric field, the polar molecular orientation of these media changes with the polarity of the electric field, which is called polarization. The stronger the applied electric field is, the stronger the polarization will be. The faster the polarization of the applied electric field changes, the faster the polarization will be. The more intense the thermal motion of the molecule and the friction between the adjacent molecules will be. In this process, the conversion of electromagnetic energy to thermal energy is completed. When heated material is placed in microwave field, its polar molecules swing and rub back and forth with the microwave frequency at several billion times per second. The heat generated is enough to make food hot in a very short time. The magnetron is used in the household microwave oven. The electric energy is converted into microwave energy by the magnetron. There are two kinds of magnetron: pulse magnetron and continuous magnetron. Continuous wave magnetron is used in microwave oven. Microwave propagation speed is close to the speed of light. It can reflect and refract in the process of propagation. It has three important characteristics related to heating. When microwave meets metal objects, such as silver, copper and aluminium, it will be reflected like a mirror reflecting visible light. Therefore, metals are commonly used to isolate microwaves. Microwave ovens are usually made of metal boxes and waveguides, and furnace doors and observation windows are made of metal mesh and tempered glass. Microwave encounters insulating materials such as glass, plastics, ceramics, mica and so on, which can pass through as smoothly as light through glass. Therefore, common insulating materials are used to make discs without affecting the heating effect. Microwave, when it comes to foods containing water or fat, can be absorbed in large quantities and converted into heat energy. Microwave ovens use this characteristic to heat food. Is there any scientific basis for microwave processing of food?

Microwave is a kind of high frequency wave, which changes at a speed of 2.4 billion times per second, causing the high-speed rotation movement of water molecules. They friction with each other to produce a great deal of heat, so they can cook food conveniently.

There are a lot of water molecules in the pathogen. Under the action of microwave in the microwave oven, all the pathogens can be killed in a minute or two. According to the determination, the red intestine containing 192,000 Escherichia coli per gram was heated in a 500-watt microwave oven. After half a minute, only 260 per gram survived and all were killed after one minute. When cooking food in microwave oven, because the heat is inside the food, the heating is uniform, without stirring, and the phenomenon of endogenous coke does not occur.

Salted meat, bacon, salted fish and smoked duck produce nitrosamines during processing. Nitrite, as a preservative, reacts with food to produce nitrosamines, which can cause cell canceration. American pharmacologists have found that cured meat is roasted in a microwave oven for 45 minutes. When taken out, it is fragrant, crisp and delicious. Moreover, chemical analysis shows no trace of imidamine. In addition, cooking meat in microwave oven can protect the nutritional components of meat food. The mysterious stainless steel chamber:

The so-called stainless steel microwave oven refers to the microwave oven whose chamber is made of stainless steel material. The so-called stainless steel is a kind of alloy steel which is melted by special process and added certain proportion of nickel, chromium and other special elements. It has high corrosion resistance. There are many kinds of stainless steel

because of its different composition and smelting process. Among them, austenitic stainless steel is not easy to be magnetized because of the particularity of its internal molecular structure. Apparently, this stainless steel can't "absorb" magnets. Therefore, it is incorrect for users to use a piece of "iron-absorbing stone" to check whether it is stainless steel. Microwave oven chamber made of stainless steel material is characterized by high surface strength, higher temperature resistance and not easy to rust.

The surface coating layer of ordinary steel plate furnace chamber treated by surface coating will fall off or crack after accidental knock, and lose its anti-rust effect on ordinary steel plate. Compared with ordinary steel plate furnace chamber treated by surface coating, stainless steel furnace chamber is not easy to rust from steel plate material, even if large pits are knocked out, it will not lose the "stainless" characteristics. It has been agreed that stainless steel is not easy to rust. For stainless steel microwave ovens in general family environment and service conditions, it can also be considered that stainless steel chambers are never rusty. The common steel plate furnace chamber treated by surface coating may also be rusted after long time use, especially in the corner area of the furnace chamber. Of course, this does not mean that the surface coated ordinary steel plate furnace chamber is very easy to rust. From the current material, process level, manufacturing cost and market acceptance, the ordinary steel plate microwave oven is not at a disadvantage, and there is no trend of being eliminated due to the introduction of stainless steel microwave oven.

As for the evaluation of some media on stainless steel microwave oven with higher heating effect and more energy-saving and time-saving, it is unavoidable that some of them are too one-sided. The surface resistance of stainless steel material is smaller than that of ordinary steel plate material treated by surface coating. Under the action of microwave, the eddy current on the surface of stainless steel material is smaller, which shows that the microwave loss of this material is smaller and the reflectivity is higher. However, this difference is not easy to see under the general family use conditions.