The role of frequency in industrial dielectric heating

A TENDENCY has developed to look upon frequency as a variable in dielectric heating which may be increased at will in order to increase the rate of heating quite independently of other factors. No doubt this tendency has been fostered by the acceptance without knowledge of its derivation of the equation for rate of dissipation of high-frequency energy in a dielectric, wherein the frequency term appears to the first power and in the numerator. The purpose of this paper is to analyze more carefully the role of frequency in industrial dielectric heating. The expression for the rate of heating will be critically examined, particularly with reference to the direct influence of frequency and its indirect influence through certain of the other variables of the heating equation that are not independent of frequency. In the light of this and other known effects of frequency, an attempt will be made to determine the practical upper limit of frequency for large-scale industrial dielectric-heating installations. It is hoped that, as a result of this discussion, there will result in the future a more precise use of the term frequency as related to dielectric heating. It should be pointed out that, in order to express the effect of frequency quantitatively, it has been necessary either to assume the ideal condition of pure L and C or to assume reasonable values of capacitance to ground and of distributed L and C. For this reason it has been possible in certain instances only to establish limits.