Microwave is a high-frequency electromagnetic wave with a frequency of 300 MHz to 300,000 MHz and a wavelength of 1 mm to 1 m. The microwave has the characteristics of short oscillation period, strong penetrating ability, and specific effects with material interaction.
Traditional drying methods, such as flame, hot air, steam, electric heating, etc., are externally heated and dried. After the surface of the material absorbs heat, the heat is transmitted to the inside of the material, and then the temperature is raised and dried. Microwave drying is completely different, it is a method of internal heating. The wet material is in a microwave high-frequency electric field with a very short oscillation period, and the water molecules inside it are polarized and arranged neatly along the direction of the microwave electric field, and then rapidly rotate with the alternating change of the direction of the high-frequency alternating electric field, and generate Violent collisions and friction (up to hundreds of millions of times per second) result in a portion of the microwave energy being converted into molecular kinetic energy, which is expressed in the form of heat, causing the temperature of the water to rise and leave the material, thereby drying the material. That is to say, after the microwave enters the material and is absorbed, its energy is converted into heat energy inside the material dielectric. Therefore, microwave drying is a drying method in which electromagnetic waves are used as a heating source and the dried material itself is a heating element.
The core of microwave drying equipment is microwave generator. At present, the frequency of microwave drying is mainly 2450 MHz. It is mostly used in the drying of chemical, food, agricultural and sideline products, wood, building materials, paper products, etc. It can also be used for food, agricultural and sideline products, etc. Sterilization.
In the conventional drying process, in order to increase the drying speed, it is necessary to raise the external temperature and increase the temperature gradient, but it is easy to produce an endogenous phenomenon of material external coke. However, when microwave heating is used, the heat can be uniformly infiltrated regardless of the shape of the material, and the expansion effect can be produced to facilitate the pulverization.
Under the action of microwave, the drying rate of the materials tends to be uniform and the heating is uniform. Moreover, the microwave drying technology does not affect the color, fragrance, taste and structure of the material to be dried, and the active ingredient is not easily broken down or destroyed. The research institutes are working on the use of microwave drying instead of the traditional drying of the drying room to solve the problem of drying unevenness caused by the drying method of traditional Chinese medicine.
The microwave equipment has fewer supporting facilities, less land occupation, convenient operation and continuous operation, which is convenient for automatic production and enterprise management (can be controlled by PLC programming and temperature adjustable).
The energy utilization rate of the microwave drying process is high, because the heat of the microwave is directly generated inside the wet material, the heat loss is small, the heat efficiency is high, and there is no environment and noise pollution, which can greatly improve the working environment.
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