Electric heater heating methods
Product heating methods
Resistance heating
Using the Joule effect of electric current to convert electrical energy into thermal energy to heat objects. It is usually divided into direct resistance heating and indirect resistance heating. In the former, the power supply voltage is directly applied to the object to be heated. When current flows, the object itself (such as an electric ironing machine) generates heat. Objects that can be directly resistance heated must be conductors but have high resistivity. Since heat is generated within the object itself, it is internal heating with high thermal efficiency. Indirect resistance heating requires special alloy or non-metallic materials to make heating elements, which generate thermal energy and transfer it to the object to be heated through radiation, convection, and conduction. Since the object and the heating element are separate, the type of object is generally unrestricted and operation is simple.
Induction heating
Using the thermal effect of induced current (eddy current) generated when a conductor is in an alternating electromagnetic field to heat the conductor itself. According to different heating process requirements, the frequency of the AC power used for induction heating includes power frequency (50-60 Hz), intermediate frequency (60-10000 Hz), and high frequency (above 10000 Hz). Power frequency power is the usual industrial AC power, with most countries using 50 Hz. The voltage applied to the induction device from the power frequency power supply must be adjustable. Depending on the power of the heating equipment and the capacity of the power grid, high-voltage power (6-10 kV) can be supplied through a transformer, or the heating equipment can be directly connected to a 380 V low-voltage grid.
Arc heating
Using the high temperature generated by an electric arc to heat objects. An arc is a gas discharge phenomenon between two electrodes. The arc voltage is not high but the current is large, maintained by a large number of ions evaporated from the electrodes, so the arc is easily affected by surrounding magnetic fields. When an arc forms between electrodes, the temperature of the arc column can reach 3000-6000 K, suitable for high-temperature melting of metals.
Electron beam heating
Using high-speed electrons moving under an electric field to bombard the surface of an object, heating it. The main component for electron beam heating is the electron beam generator, also called an electron gun. The electron gun mainly consists of a cathode, a focusing electrode, an anode, electromagnetic lenses, and deflection coils. The anode is grounded, the cathode is connected to a high negative potential, the focusing electrode is usually at the same potential as the cathode, and an accelerating electric field is formed between the cathode and anode. Electrons emitted from the cathode are accelerated to very high speeds under the accelerating electric field, focused by electromagnetic lenses, and then controlled by deflection coils to direct the electron beam toward the object to be heated.
Infrared heating
Using infrared radiation on objects; the object absorbs infrared and converts radiant energy into thermal energy for heating.
Dielectric heating
Using high-frequency electric fields to heat insulating materials. The main heating target is dielectrics. When a dielectric is placed in an alternating electric field, it is repeatedly polarized (the phenomenon where equal and opposite charges appear on the surface or inside the dielectric under the action of an electric field), thereby converting electrical energy in the field into thermal energy.
