Microwave vacuum evaporation of sugar solutions: Analysis of dielectric and microwave absorption properties

Microwave vacuum evaporation (MVE) is a promising alternative over traditional vacuum evaporation, offering rapid evaporation rates and high efficiency. This study investigated the MVE processes and the resulting quality of sugar solutions under varying microwave power densities (10–50 W/g) and vacuum levels (40–80 kPa). The results indicated that a moderate microwave power density (∼30 W/g in this study) was optimal for MVE, balancing both evaporation efficiency and sugar quality. Furthermore, the dielectric properties of the sugar solutions during MVE (over the temperature range of approximately 25-110°C) exhibited a time-dependent decrease in the dielectric constant (ε′), whereas both the dielectric loss factor (ε′′) and loss tangent (tanδε) initially decreased before increasing. Similar values of ε′′ and tanδε were observed for sugar solutions evaporated at high power densities, accounting for the phenomenon of saturated evaporation. The penetration depth, reflection loss, and relative input impedance results indicated that the 4 mm-thick sugar solutions exhibited good microwave absorption during the MVE, except at the initial and final stages, confirming the feasibility of utilizing a liquid film configuration in MVE applications. In conclusion, the analysis of dielectric and microwave absorption properties offers a robust approach for optimizing the MVE process, facilitating the production of high-quality sugars.