A comparative study of HF and microwave drying of milk

Dielectric properties of milk are studied over a broad range of frequencies by using the time-domain reflectometry method. Experimental results are given for the real and imaginary parts of the permittivity for frequencies of 15, 30, and 100 MHz (high-frequency range) and 915, 2450, and 5800 MHz (microwave range). The choice of these frequencies corresponds to standards in the use of HF and MW power applications. The effects are shown 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 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 that can be defined for a particular (spherical) geometry of milk particles