The common heating ways are listed for you. (3)
1, infrared heating: the use of infrared radiation objects, objects absorb infrared radiation energy into heat and be heated.
Infrared ray is a kind of electromagnetic wave. In the solar spectrum, outside the red end of visible light, is an invisible form of radiant energy. In the electromagnetic spectrum, infrared wavelengths range from 0.75 to 1000 microns and frequencies range from 3×10 to 4×10 Hertz. In industrial applications, infrared spectrum is often divided into several bands: 0.75 ~ 3.0 micron near infrared region; 3.0-6.0 micron is medium infrared region. 6.0 ~ 15.0 micron is far infrared region. 15.0 ~ 1000 micron is the far infrared region. Different objects have different ability to absorb infrared rays, even the same object has different ability to absorb infrared rays of different wavelengths. Therefore, the application of infrared heating, according to the type of heated object, to choose the right infrared radiation source, make its radiation energy concentrated in the absorption wavelength range of the heated object, in order to get a good heating effect.
Electric infrared heating is actually a special form of resistance heating, that is, tungsten, ferro-nickel or nickel-chromium alloy is used as the radiator to make the source of radiation. When energized, thermal radiation is produced by the heating of its resistance. The commonly used sources of electric infrared heating radiation are lamp type (reflection type), tube type (quartz tube type) and plate type (plane type). Lamp type is an infrared bulb, with tungsten wire as the radiator, tungsten wire sealed in a glass shell filled with inert gas, like ordinary lighting bulb. The radiator heats up with electricity (at a lower temperature than a typical lighting bulb), emitting a lot of infrared light with a wavelength of about 1.2 microns. If a reflective layer is plated on the inner wall of the glass shell, the infrared radiation can be concentrated in one direction, so the lamp type infrared radiation source is also known as the reflector. Tube type infrared radiation source tube is made of quartz glass, the middle is a tungsten wire, it is also known as the quartz tube type infrared radiator. The wavelength of infrared ray emitted by lamp and tube is in the range of 0.7 ~ 3 micron, and the working temperature is low. The radiant surface of the plate-type infrared radiation source is a flat surface, which is composed of a flat resistance plate. The front of the resistance plate is coated with the material with high reflection coefficient, and the back is coated with the material with low reflection coefficient, so most of the heat energy is radiated from the front. The working temperature of the plate can reach more than 1000℃, which can be used for anneal of welding seams of steel materials and large diameter pipes and containers.
2. Medium heating: insulation materials are heated by high-frequency electric field. The main heating object is the dielectric. A dielectric placed in an alternating electric field will be repeatedly polarized (when the electric field is applied to the dielectric, the surface or interior of the dielectric will have the same amount of charge with opposite polarity), thus turning the electric energy in the electric field into heat energy.
The electric field used for dielectric heating is very high frequency. In the medium, short and ultrashort wave bands, the frequency of several hundred KHZ to 300 MHZ, known as high-frequency medium heating, if higher than 300 MHZ, reach the microwave band, known as microwave medium heating. The heating of high frequency medium is usually carried out in the electric field between two plates. The heating of microwave medium is carried out under the radiation field of waveguide, resonator or microwave antenna.
When the dielectric is heated in the high-frequency electric field, the electric power absorbed per unit volume is P=0.566fE epsilon epsilon tg ×10 (w/cm).
In terms of heat, H=1.33 delta epsilon epsilon tg (calorie/second · cm)
Where, f is the frequency of high-frequency electric field, epsilon and loss r is the relative dielectric constant of dielectric medium, delta dielectric loss Angle, and E is the electric field intensity. According to the formula, the electric power absorbed by the dielectric from the high-frequency electric field is proportional to the square of the electric field intensity E, the frequency f of the electric field and the loss Angle of the dielectric. E and f are determined by the applied electric field, and the epsilon and epsilon r depends on the properties of the dielectric itself. Therefore, the object of medium heating is mainly the substance with larger medium loss.
Medium heating because heat is generated inside the dielectric (the object being heated), it is heated more quickly, more efficiently, and more evenly than other external heating.
Medium heating is used industrially to heat hot gels, dry grains, paper, wood, and other fibrous materials; Also can be preheated plastic molding, and vulcanization of rubber and wood, plastic, etc. Selecting the appropriate electric field frequency and device can heat only the adhesive glue while heating the plywood without affecting the plywood itself. For homogeneous materials, monolithic heating is possible.
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