Microwave Drying Principle:
Microwaves are a type of electromagnetic wave with extremely short wavelengths, ranging from 1mm to 1m, corresponding to frequencies between 300GHz and 300MHz. To prevent interference with radio communication, broadcasting, and radar, internationally, four frequency bands are designated for microwave heating and drying: L-band, with a frequency of 890 to 940MHz and a central wavelength of 330mm; S-band, with a frequency of 2400 to 2500MHz and a central wavelength of 122mm; C-band, with a frequency of 5725 to 5875MHz and a central wavelength of 52mm; and K-band, with a frequency of 22000 to 22250MHz and a central wavelength of 8mm. Only L-band and S-band are used in residential microwave ovens.
Microwaves are generated by passing direct current or a 50Hz alternating current through electric vacuum or semiconductor devices, utilizing the special movement of electrons in a magnetic field. This movement can be explained simply as follows: From an electrical structure perspective, there are two types of dielectric molecules: non-polar and polar. Generally, they are arranged randomly. If placed in an alternating electric field, the orientation of the polar molecules in these dielectrics changes with the field's polarity, which is known as polarization. The stronger the applied electric field, the stronger the polarization effect, and the faster the field's polarity changes, the quicker the polarization occurs. This results in more intense thermal motion and friction between adjacent molecules. During this process, electromagnetic energy is converted into thermal energy. When the material to be heated is placed in a microwave field, its polar molecules oscillate and rub against each other at a frequency of several billion times per second, corresponding to the microwave frequency.
The generated heat is sufficient to achieve the thermal drying of materials in a very short time.
Advantages of Microwave Drying:
Selective heating. Since water molecules absorb microwaves well, areas with higher water content absorb more microwave power than those with lower water content. This is the characteristic of selective heating, which can be utilized to achieve uniform heating and drying.
2. Energy-efficient. Microwave acts directly on the material, resulting in no additional heat loss. The air inside the oven and the corresponding container do not heat up, thus achieving high thermal efficiency and significantly improving the production environment. Compared to far-infrared heating, it can save electricity by 30%.
3. Shorter duration, higher efficiency. Microwave heating causes the heated object to become a heat source itself, without the need for heat conduction. Microwaves penetrate the object from all directions, both internally and externally, uniformly heating the object in a very short time, significantly reducing the drying time.
4. Easy to control and equipped with advanced technology, the equipment is ready for use immediately upon opening. It boasts no thermal inertia, offering flexible and convenient operation; microwave power and transmission speed are adjustable. In microwave heating and drying processes, there is no waste water or emissions, making it a safe and harmless high-tech solution.
