Microwaves are electromagnetic waves, electromagnetic waves with a frequency of 300 MHz to 300 GHz (wavelengths of 1 m - 1 mm), which are usually used as information transmission in radar and communication technologies.
Microwave heating characteristics1. Heating speed is fast. Conventional heating such as flame, hot air, electric heat, steam, etc., all use the principle of heat conduction to transfer heat from the outside of the object to be heated, and gradually increase the temperature of the center of the object, which is called external heating. It takes a certain amount of time for the center to reach the desired temperature, and the object with poor thermal conductivity takes longer. Microwave heating is a method in which the object to be heated itself becomes a heating element, which is called an internal heating method, and does not require heat conduction. The inside and the outside are simultaneously heated, so that the heating effect can be achieved in a short time.
2. Uniform heating of conventional heating. In order to increase the heating rate, it is necessary to raise the heating temperature, which is prone to external endogenous phenomena. When microwave heating, the parts of the object generally permeate electromagnetic waves uniformly, generating heat, so the uniformity is greatly improved.
3. Energy-saving and high-efficiency In microwave heating, microwave energy can only be absorbed by heated objects and heat is generated. The air in the heating chamber and the corresponding container will not generate heat, so the thermal efficiency is extremely high and the production environment is also obviously improved.
4. The thermal inertia of microwave heating is easy to control. If equipped with microcomputer control, it is especially suitable for the automatic control of the heating process.
5, low temperature sterilization, non-polluting microwave energy itself will not be contaminated by food, the thermal effect of microwave double sterilization can kill bacteria at lower temperatures, which provides a kind of heat sterilization that can maintain more food nutrients method.
6. Selective heating of microwaves has different effects on materials of different properties, which is beneficial for drying operations. Because the water molecules absorb the microwaves best, the part with high water content absorbs microwave power more than the water content is lower. This is the characteristic of heating. When drying wood, paper and other products, this feature can be used to achieve uniform heating and uniform drying.
It is worth noting that some substances have higher temperature and better absorption, resulting in a vicious cycle. When local temperature rises sharply, it causes excessive drying or even carbonization. When microwave heating of such materials, attention should be paid to formulating a reasonable heating process.
7. Safe and harmless In the microwave heating and drying, no waste water, waste gas, waste is generated, no radiation remains, and the microwave leakage is also guaranteed to be much lower than the safety standards set by the state. It is a very safe and harmless high-tech. technology.
Ultrasound is a sound wave: a sound wave with a frequency higher than the upper limit of human hearing (about 20,000 Hz), called ultrasonic wave, or ultrasonic.
The laws of reflection, refraction, diffraction, and scattering of ultrasonic waves in the medium are not fundamentally different from the laws of audible sound waves. But the wavelength of the ultrasound is very short, only a few centimeters, or even a few thousandths of a millimeter. Compared with audible sound waves, ultrasonic waves have many singular characteristics: propagation characteristics - the wavelength of ultrasonic waves is very short, and the size of ordinary obstacles is many times larger than the wavelength of ultrasonic waves, so the diffraction power of ultrasonic waves is very poor, and it is in a uniform medium. The ability to direct linear propagation, the shorter the wavelength of the ultrasonic wave, the more significant this characteristic. Power characteristics - When the sound travels in the air, it pushes the particles in the air to reciprocate and work on the particles. The sound power is the physical quantity that indicates how fast the sound wave works. At the same intensity, the higher the frequency of the sound wave, the greater the power it has. Since the ultrasonic frequency is high, the power of the ultrasonic wave is very large compared to the general sound wave. Cavitation - When ultrasonic waves propagate through a liquid, small holes are created inside the liquid due to the intense vibration of the liquid particles. These small cavities rapidly swell and close, causing a violent impact between the liquid particles, resulting in pressures of thousands to tens of thousands of atmospheres. This violent interaction between the particles causes the temperature of the liquid to rise suddenly, which acts as a good agitation, emulsification of the two immiscible liquids (such as water and oil), and accelerates the dissolution of the solute and accelerates chemical reaction. This various effects caused by the action of ultrasonic waves in the liquid are called cavitation of the ultrasonic waves.
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