I. Working Principle:Air duct electric heater : heat is generated by an electrical heating element placed in the heater. It is to heat the medium by means of forced convection,when the medium enters the vessel through the entrance of the container. The principle of fluid thermodynamics is adopted during heating to transfer the huge heat generated when the electric heater works. When the temperature of the medium is close to the set value, the control system of the electric heater carries out PID calculation according to the signal of the outlet temperature sensor, and automatically adjusts the output power of the heater, so that the outlet temperature of the medium meets the required requirements; When the outlet temperature exceeds the upper limit of the set value, the electric heater will be automatically cut off immediately to avoid burning out the heating element and extend the service life.