关键词: 热物理特性, 介电特性, 紫薯, 热风微波耦合干燥, 预测方程

Abstract: Thermephysical （density， thermal conductivity， specific heat， and thermal diffusivity） and dielectric properties （dielectric constant and dielectric loss factor） of purple sweet potato were studied by dielectric spectrometer （E5062A） and thermal characteristic analyzer （KD2 Pro） within 20 to 100℃， 10.0% to 74.2%（w.b.） moisture content and 900 to 3 000 MHz frequency. It was shown that the density decreased with temperature and moisture content. Increasing temperature or moisture content could increase the thermal conductivity， specific heat， and thermal diffusivity of purple sweet potato. Frequency， temperature and moisture content significantly affected the dielectric constant and dielectric loss factor of purple sweet potato. Dielectric constant decreased， but dielectric loss factor firstly decreased， and then increased with the increasing of frequency. Dielectric constant and temperature were apparently negaively correlated with each other， but dielectric constant and moisture were positively correlated with each other. There was positive correlation between dielectric loss factor and temperature and moisture. At the frequency of 2 450 MHz， predictive equations were developed for dielectric constant and dielectric loss factor as a function of temperature and moisture content. Besides， The penetration depth showed negative correlation with temperature and moisture content.

Key words: thermophysical property, dielectric property, purple sweet potato, combined hot\, air and microwave drying, predictive equations