Dielectric properties of eggshell powder at 2.45 and 5.8 GHz relevant to dielectric heating

In present studies, dielectric properties of eggshell powder were determined at microwave frequencies 2.45 and 5.8 GHz by varying temperature and moisture content in the range 15–75 °C and 0.5–8% (wet-basis) respectively, using cavity perturbation technique. Values of dielectric constant (ε′) and loss factor (ε″) increase with temperature and moisture content at both of these frequencies but ε′ is higher at 2.45 GHz than 5.8 GHz whereas ε″ shows opposite trend. The calculated penetration depths of microwaves are more at 2.45 GHz than 5.8 GHz and it decreases with increase in temperature as well as moisture content. The determined data of ε′ and ε″ were used to generate the third order regression equations with high correlation coefficients (R2 > 0.95). These findings are useful for modelling and designing the microwave applicator for heat treatment to eggshell powder. Additionally, X-ray diffraction spectra was also recorded.