A COMPARATIVE-STUDY OF HF AND MICROWAVE DRYING OF MILK

Dielectric properties of milk were studied over a broad range of frequencies from 1 to 10 MHz by using the time domain reflectometry method. Experimental results are given for the real and imaginary parts of the permittivity for frequencies 15, 30, 100 (HF range), 915, 2450, and 5800 MHz (MW range). The choice of these frequencies corresponds to standards in the use of HF and MW power applications. This paper shows the effects of the variation of the temperature and water concentration of milk on the complex permittivity. The efficiency of the process for the dehydration of milk, by using HF or MW power, is given for different frequencies, temperatures, and water concentrations. It is concluded that the efficiency of the dehydration process is largely determined by a power absorption factor K, defined for a particular (spherical) geometry of milk particles. © 1990 IEEE