Introduction
Converting electrical energy into thermal energy to heat objects is a form of electrical energy utilization. Compared with general fuel heating, electric heating can achieve higher temperatures (e.g., arc heating can reach temperatures above 3000°C), and it is easy to realize automatic temperature control and remote control, vehicle-mounted electric heating cup.
It can maintain a certain temperature distribution of the heated object as needed. Electric heating can generate heat directly inside the heated object, thus having high thermal efficiency and fast heating speed. According to the heating process requirements, it can achieve uniform overall heating or local heating (including surface heating), and it is easy to realize vacuum heating and controlled atmosphere heating. During the electric heating process, there is less waste gas, residue, and dust, keeping the heated object clean and not polluting the environment. Therefore, electric heating is widely used in production, scientific research, and testing fields. Especially in the manufacturing of single crystals and transistors, mechanical parts and surface quenching, smelting of ferroalloys, and manufacturing of artificial graphite, electric heating methods are adopted.
Classification
According to different methods of electrical energy conversion, electric heating is usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating, and dielectric heating.
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 heated object, and when current flows, the heated object itself generates heat. Electric heating ironing machine.
Objects that can be directly resistance heated must be conductors with high resistivity. Since heat is generated inside the heated object itself, it is internal heating with high thermal efficiency. Indirect resistance heating requires special alloy materials or non-metallic materials to make heating elements, which generate thermal energy and transfer it to the heated object through radiation, convection, and conduction. Since the heated object and the heating element are separated, the type of heated object is generally not limited, and operation is simple.
The materials used for heating elements in indirect resistance heating generally require high resistivity, low temperature coefficient of resistance, small deformation at high temperatures, and not easy to embrittle. Commonly used are iron-chromium-aluminum alloys, nickel-chromium alloys and other metal materials, as well as silicon carbide, molybdenum disilicide and other non-metallic materials. The maximum working temperature of metal heating elements can reach 1000~1500°C depending on the material; the maximum working temperature of non-metallic heating elements can reach 1500~1700°C. The latter is easy to install and can be replaced in a hot furnace, but it requires a voltage regulating device during operation and has a shorter lifespan than alloy heating elements. It is generally used in high-temperature furnaces, places where the temperature exceeds the maximum working temperature allowed for metal material heating elements, and some special occasions.
