电流热效应原理：电子在电场中得到加速，获得动能，具有速度，然后碰撞其他的微粒（原子，分子，原子团，….）使其他的微粒获得动能，导致平均动能增大，温度升高. 焦耳-楞次定律： 电流通过电阻时，电阻就会发热，将电能转换为热能，这种现象叫做电流的热效应。 焦耳和楞次通过大量的试验，发现电阻通过电流后所产生的热量与电流的平方、电阻及通电时间成正比。这就是是焦耳-楞次定律。 电能转换为热能的关系可用公式表示：Q=（I的二次方）Rt I=电流;R=电阻;t=时间；Q=电阻上产生的热量。
Current heating principle: electronic accelerated in the electric field, gain kinetic energy, has the speed and crash other particles (atoms, molecules, atoms, etc.) Give other particle kinetic energy, which leads to the average kinetic energy increases, the temperature rise. Joule – lenz’s law: the current through the resistance, the resistance will be fever, converts electrical energy into heat energy, this phenomenon is called the heating effect of the current. Joule and lenz through a large number of trials, found that the heat generated by the resistance by the current and the square of the current, resistance, and is proportional to the current time. This is what is the joule – lenz’s law. Available formula for the relation of the electrical energy is converted to heat energy, said: Q = quadratic (I) Rt I = current; R = resistance; T = time. Q = the heat generated by the resistance.
Now to explain the different heating principle of electric heater is used to:
The joule effect of using current transform electric energy into heat energy to heat the object。 Usually divided into direct resistance heating and indirect resistance heating。 Power supply voltage of the former directly to the heated object, when have a current flows through the heated object itself, such as electric heating ironing machine) and fever。 Direct resistance heating object must be a conductor, but must have the high resistivity。 Due to the heat generated by heated object itself, belongs to the internal heating, high thermal efficiency。 Indirect resistance heating should be made of special alloy materials or non-metallic materials, heating element, heat generated by the heating element, through radiation, convection and conduction to the heated object。 Because of the heated object is divided into two parts and heating elements, so heated object types is generally not restricted, easy to operate。
Indirect resistance heating heating element materials, general requirements resistivity, temperature coefficient of resistance small, little deformation at high temperature and not easily embrittlement. Commonly used a iron alloy, nickel chromium alloy and other metal materials and silicon carbide, such as molybdenum disilicide non-metallic materials. The highest working temperature, metal heating element according to the types of materials can reach 1000 ~ 1000 ℃; Non-metallic heating element of the highest working temperature is 1500 ~ 1700 ℃. Which features easy installation, can change hot stove, but it requires pressure regulating device at work, life, shorter than alloy heating elements, commonly used in high temperature furnace, temperature more than metal materials heat element allows the highest working temperature place, and some special occasions.