Effective diffusivities and energy consumption of daylily in microwave drying

Drying kinetics of fresh daylily flower buds (Hemerocallis Citrine Baroni cv. Mengzihua) in a microwave oven at 60, 120, 180 and 240 W, respectively, were investigated. The results indicated that, drying rate increased at the initial time (a warm-up period) and then decreased at the end time (a falling rate period) after reaching a plateau (a constant rate period). A third-order polynomial model could well describe the relationships between effective diffusivity and moisture content, and the model's coefficients correlated linearly with microwave power level. A logistic model could well present the relationships between activation energy and moisture content. The curves of energy consumption vs. microwave power level indicated that in the initial phase of drying, the energy utilisation efficiency was almost the same at different microwave output power levels; however, at the end phase of drying, drying at lower microwave levels was worse in energy utilisation.