Dielectric heating is also sometimes called as high frequency capacitance heating.
If non metallic materials ie, insulators such as wood, plastics, china clay, glass, ceramics etc are subjected to high voltage A.C current, their temperature will increase in temperature is due to the conversion of dielectric loss into heat.
The dielectric loss is dependent upon the frequency and high voltage. Therefore for obtaining high heating effect high voltage at high frequency is usually employed.
The metal to be heated is placed between two sheet type electrodes which forms a capacitor as shown in fig. The equivalent circuit and vector diagram is also shown in fig.
When A.C supply is connected across the two electrodes, the current drawn by it is leading the voltage exactly 90˚.
The angle between voltage and current is slightly less than 90˚
But at high frequencies, the loss becomes large, which is sufficient to heat the dielectric.
ü Uniform heating is obtained.
ü Running cost is low.
ü Non conducting materials are heated within a short period.
ü Easy heat control.
ü For food processing.
ü For wood processing.
ü For drying purpose in textile industry.
ü For electronic sewing.
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