Principle and application of resistance heating
It uses the Joule effect of electric current to convert electrical energy into thermal energy to heat objects. Usually divided into direct resistance heating and indirect resistance heating. The power supply voltage of the former is directly applied to the object to be heated, and when current flows, the object to be heated will generate heat.
The object that can be directly resistance heated must be a conductor, but it must have a higher resistivity. Since the heat is generated by the heated object itself, it belongs to internal heating, and the thermal efficiency is very high. Indirect resistance heating requires special alloy materials or non-metallic materials to make heating elements. The heating elements generate heat, which is transmitted to the object to be heated by means of radiation, convection and conduction. Since the heated object and the heating element are divided into two parts, the type of the heated object is generally not limited, and the operation is simple.
The materials used for heating elements of indirect resistance heating generally require high resistivity, low temperature coefficient of resistance, small deformation at high temperatures and not easy to embrittlement. Commonly used are iron-aluminum alloy, nickel-chromium alloy and other metal materials; silicon carbide, molybdenum disilicide and other non-metallic materials; there are resistance pastes, such as carbon paste, precious metal pastes such as tungsten/palladium silver/ruthenium/platinum paste and Semiconductor rare earth, etc.
The maximum working temperature of metal heating elements can reach 1000～1500℃ depending on the type of material; the highest working temperature of non-metal heating components can reach 1500～1700℃. The latter is easy to install and can be made into various shapes such as flat/curved/abnormity. It is easy to be effectively attached to the heated body or load. Some material elements can be made into high-power density chip heating devices (such as thick film resistance/heating Components), the life is 5-10 times that of traditional alloy wires, and the voltage application range is wider, and the resistance value can be very small (чΩ) to very large (such as MΩ). It is a high-tech printing of the latest HOS process The product has been widely used in foreign countries. It is only after years of development in China that it is only applied in occasions where the heating device is extremely demanding, but it has been applied in batches in military/aerospace/aerospace fields.
