The object that can be heated by direct resistance must be a conductor, but it must have a high resistivity. Because the heat is generated by the heated object itself, which belongs to internal heating, the thermal efficiency is very high. Indirect resistance heating needs to be made of special alloy materials or non-metallic materials into heating elements, which generate heat energy and transmit it to the heated object by means of radiation, convection and conduction. As the heated object and the heating element are divided into two parts, the types of heated objects are generally unlimited and easy to operate.
The Joule effect of electric current is used to transform electric energy into heat energy to heat objects. It is usually divided into direct resistance heating and indirect resistance heating. The power supply voltage of the former heating tube is directly applied to the heated object. When there is current flowing through, the heated object itself (such as electric heating ironing machine) will heat up.