DIELECTRIC HEATING • Dielectric heating is also called high-frequency capacitive heating. • It is used for heating insulators like wood, plastics and ceramics etc. which cannot be heated easily and uniformly by other methods. • The supply frequency required for dielectric heating is between 10-50 MHz and the applied voltage is up to 20 kV. • The overall efficiency of dielectric heating is about 50%.
DIELECTRIC HEATING • When non – metallic parts such as wood, plastics are subjected to an alternating electrostatic field dielectric loss occurs. • In dielectric heating these losses are made use of. • The material to be heated is placed as a slab between metallic plates or electrodes connected to a high frequency AC supply. • For producing sufficient heat, frequency between 10 and 30 MHz is used. • Voltage applied will be in the range 600V – 3kV.
DIELECTRIC HEATING • The current drawn by the capacitor, when an ac supply voltage is applied across its two plates, does not lead the supply voltage by exactly 90 0 . • There is always an in phase component of the current. • Due to the in phase(active) component of the current, heat is always produced in the dielectric material placed in between the two plates of the capacitor. • The electric energy dissipated in the form of heat energy in the dielectric material is known as dielectric loss. • The dielectric loss is directly proportional to the frequency of AC supply given to the two plates of the capacitor. • The dielectric loss is the molecular friction in the dielectric material when an AC electrostatic field is applied to it.
DIELECTRIC HEATING • Since insulators are poor conductors, they cannot be heated quickly from outside. • In dielectric heating, the heat is produced within the material itself. • The heat generation is uniform, therefore the dielectric material is heated uniformly.
- Fall '14
- H N SHANKAR