Question

2. what is dielectric heating? derive an expression for the heat produced in a dielectric material

Answer 1

The advantages of dielectric heat for drying, cooking, thawing, and melting of foods are that heat generation is rapid and occurs throughout the body of the food material. An additional advantage for drying is that water is heated more quickly than the other components of the food. In conventional methods of drying, heat is transferred to the surface of the food by convection, conduction, or radiation. It has then to transfer throughout the body of the food by conduction. Some penetration does occur in the case of radiant heat but this is limited and often difficult to control. The penetration of electromagnetic waves in the dielectric range into materials such as foods depends on frequency and the characteristics of the material. The lower the frequency, hence the longer the wavelength, the greater the penetration. Penetration may be quantified by half-power depth, i.e., the thickness of the material, which reduces the wave energy to 50% of the incident level. The half-power depth for water is about 12 mm at a frequency of 2450 MHz and 75 mm at 100 MHz. Penetration into foods is less than into water.

Answer 2

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