The laboratory USES the heating plate to analyze three different ways of electric heating for you
According to different energy conversion modes, electric heating with heating plates in laboratories can be generally divided into the following categories: resistance heating, induction heating, arc heating, electron beam heating, infrared heating, and medium heating. Among them, zui is commonly used for resistance heating, infrared heating, and arc heating.
1, infrared heating: the use of infrared radiation objects, objects absorb infrared radiation energy into heat and be heated. 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, tube type and plate 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. Due to its strong penetrating ability, infrared ray is easy to be absorbed by objects, and once it is absorbed by objects, it is immediately transformed into heat energy. The application of infrared heating develops rapidly because of its low energy loss, easy temperature control and high heating quality.
2. Resistance heating: use the joule effect of current to convert electrical energy into heat energy to heat an object. Usually divided into direct resistance heating and indirect resistance heating. The power supply voltage of the former is directly applied to the heated object. When there is a current flowing through the heated object itself, the ironing machine is electrically heated
And fever. An object that can be heated directly by resistance must be a conductor with a high resistivity. Since the heat is generated from the heated object itself, it is internal heating, and the thermal efficiency is very high. Indirect resistance heating requires heating elements made of special alloy or non-metallic materials, which generate heat energy that is transmitted to the heated object by means of radiation, convection and conduction. As the heated object and heating element are divided into two parts, the type of heated object is generally unlimited and easy to operate. The material used for heating element of indirect resistance heating is generally required to have large resistivity, small resistance temperature coefficient, small deformation and not easy embrittlement at high temperature. There are commonly used iron aluminum alloy, nickel chromium alloy and other metal materials and silicon carbide, molybdenum disilicide and other non-metallic materials. The zui high operating temperature of metal heating element can reach 1000 ~ 1500℃ according to the material type. The high operating temperature of zui can reach 1500 ~ 1700℃. The latter is easy to install and can be replaced by hot furnace, but it needs pressure regulating device when working, and its service life is shorter than that of alloy heating element. It is generally used in high temperature furnace, where the temperature exceeds the high working temperature allowed by metal heating element zui and some special occasions.
3. Arc heating: use the high temperature generated by arc to heat objects. Arc is the phenomenon of gas discharge between two electrodes. The arc's voltage is low but its current is high. Its strong current is maintained by a large number of ions vaporized on the electrode, so the arc is susceptible to the influence of the surrounding magnetic field. When an arc is formed between electrodes, the temperature of arc column can reach 3000 ~ 6000K, which is suitable for high temperature melting of metal. Arc heating has direct and indirect arc heating. The arc current from direct arc heating passes directly through the heated object, which must be an electrode or medium of the arc. The arc current of indirect arc heating does not pass through the heated object. The characteristics of arc heating are: high arc temperature, energy concentration, steel arc furnace melting pool surface power can reach 560 ~ 1200 kw/m2. However, the noise of arc is large, and its volt-ampere characteristic is negative resistance characteristic (descending characteristic). In order to maintain the stability of the arc when the arc is heated, the instantaneous value of the circuit voltage when the arc current instantaneous passes zero is greater than the value of the arc starting voltage, and in order to limit the short-circuit current, a certain number of resistors must be connected in series in the power circuit.