Microwave heating principle and characteristics      Microwaves, like radio waves, television signals, radar communications, infrared, visible light, etc., are electromagnetic waves, but the wavelengths are different. Frozen Garlic,Iqf Frozen Garlic,Natural Garlic Elites-United Foodstuff Co., Ltd. , http://www.qdiqfvegetables.com
Microwaves are electromagnetic waves (wavelengths of 1 m -1 mm) with frequencies between 300 MHz and 300 GHz. They are commonly used in television, broadcasting, and communication technologies, and in modern applications they are extended to another branch, that is, microwaves. Energy, heating and drying in industry and agriculture; catalyzed chemical reaction in the chemical industry; excitation of plasma, etc. The use of household microwave ovens is also becoming more widespread. Since the application of electromagnetic waves is extremely extensive and widespread, in order to avoid mutual interference, the International Radio Regulatory Commission has specified the frequency division. The frequencies currently used for industrial heating in China are 915 MHz and 2,450 MHz.
 Microwave heating principle
The dielectric material consists of polar molecules and non-polar molecules. Under the action of an electromagnetic field, these polar molecules are shifted from the original random distribution state to the polarity of the electric field. Under high frequency electromagnetic action, these orientations change as a function of the alternating electromagnetic field, which causes the molecules to move and rub against each other to generate heat. At this time, the field energy of the alternating electromagnetic field is converted into the thermal kinetic energy in the medium, so that the temperature of the medium is continuously increased, which is the basic principle of microwave heating.
It can be seen that the microwave heating is that the dielectric material itself loses electric field energy and generates heat. For the conductive metal material, the electric wave cannot penetrate into the interior and is reflected, and the metal material cannot absorb the microwave. The dielectric material has different effects under the action of microwave electromagnetic field because of its dielectric constant ε r and dielectric loss tangent tgδ .
A substance composed of polar molecules can absorb microwaves well. Water molecules that can be heated by microwaves are polar molecules and are the best medium for absorbing microwaves. Therefore, aqueous medium materials must absorb microwaves.
The other type consists of non-polar molecules, which do not absorb or absorb microwaves. These materials are plastic products such as polytetrafluoroethylene and polypropylene, and glass, ceramics, etc., which can pass through microwaves without absorption. Microwave, this material can be used as a container or support for microwave heating, or as a microwave sealing material.
In the microwave electric field, the absorption and conversion of microwave by the medium into thermal energy is proportional to the operating frequency of the microwave, the square of the electric field strength, the dielectric constant and the dielectric loss tangent.
In the actual heating process, there is a problem of penetrating ability and heating depth. The penetrating ability is the ability of electromagnetic waves to penetrate into the medium. When electromagnetic waves enter from the surface of the medium and propagate inside, the energy is continuously absorbed and converted into Heat, the energy it carries, decays exponentially with the distance from the surface of the medium.
1 , heating speed is fast
Conventional heating, such as flame, hot air, electric heat, steam, etc., uses the principle of heat conduction to transfer heat from the outside of the object to be heated, and gradually raises the temperature of the center of the object, which is called external heating. In order to achieve the desired temperature in the center, it takes a certain time and requires a higher external temperature; the object with poor thermal conductivity takes a long time. Microwave heating is to make the object to be heated itself a hot object. It is called the overall heating method, and does not require heat transfer. Therefore, it can be uniformly heated in a short time. This feature allows the material with poor heat conduction to be heated and dried in a short time, the energy utilization rate is improved, and the size of the heating furnace can be made smaller than that of the conventional heating furnace.
2 , uniform heating
In the external heating method, in order to increase the heating speed, it is necessary to raise the external temperature, which is easy to produce a " shell " of the outer layer and a " green " phenomenon of the inner layer. Regardless of the shape of the various parts of the object during microwave heating, it is generally possible to uniformly penetrate electromagnetic waves to generate heat, so that the ineffectiveness of heating of the dielectric material is greatly improved.
3 , energy efficient
Microwaves have different effects on different substances, and polar substances easily absorb microwave energy and generate heat. Without polarity, it rarely absorbs microwave heating. When microwave heating, the material to be heated is generally placed in a heating chamber made of metal. The heating chamber is a closed cavity for the electric wave, the microwave can not be leaked, can only be absorbed by the heating object, and the air in the heating chamber is correspondingly The container does not generate heat, so the thermal efficiency is extremely high, and the ambient temperature of the workshop will not increase accordingly, and the labor production environment is obviously improved.
4 , easy to control
Compared with the conventional heating method, the microwave heating control can instantaneously achieve the purpose of lifting, opening and stopping as long as the power control knob is operated. Because only the object itself is heated during heating, the air in the furnace body and the furnace chamber is hardly heated, so the thermal inertia is extremely small, and the computer control is applied, which is particularly suitable for the specification and automatic control of the heating process and the heating process.
5 , clean and hygienic
When heating food and medicine, the biological effect of microwave can kill bacteria at a lower temperature, which provides a heat sterilization method that can maintain more nutrients of food, so microwave heating is obtained in the food industry. A wide range of applications.
6 , selective heating
Microwaves have different effects on materials with different media properties, which is advantageous for dry processing characteristics. Because water molecules are best for microwaves and absorption, the part with high water content absorbs microwave power more than the water content, which is the characteristic of microwave selective heating. When drying wood, paper and other products, this feature can be used to achieve uniform heating and uniform drying. It should be noted that the higher the temperature, the better the absorption of some substances, and the positive feedback causes the temperature of this part to rise sharply. When carrying out microwaves for such substances, care should be taken to establish a reasonable heating process.
7 , safe and harmless
Generally, microwave energy is operated in a closed heating chamber made of metal and a waveguide, so the leakage of energy is extremely small. The microwave equipment manufactured by our company adopts advanced design and excellent processing, so the inlet and outlet, observation window and furnace Microwave sinks at gates and other places are minimal, which is far superior to national safety standards. Moreover, microwaves have no radiation hazards and harmful gas emissions, and are a very safe heating technology.