Energy analyses and drying kinetics of chamomile leaves in microwave-convective dryer

Drying characteristics and energy aspects as well as mathematical modeling of thin layer drying kinetics of chamomile in a microwave-convective dryer are reported in this article. Drying experiments were carried out at 8 microwave power levels (200–900 W), air temperature of 50 °C, and air velocity of 0.5 m/s. Increasing the microwave output power from 200 to 900 W, decreased the drying time from 40 to 10 min. The drying process took place in the falling rate period. The Midilli et al. model showed the best fit to the experimental drying data. Moisture diffusivity values increase with decreasing moisture content down to 1.70 (kg water kg^-1 dry matter) but decrease with a further decrease in moisture content from 1.72 to 0.96 (kg water kg^-1 dry matter). The average values of Deff increased with microwave power from 5.46 to 39.63 · 10^-8 (m^2 s^-1). Energy consumption increased and energy efficiency decreased with moisture content of chamomile samples. Average specific energy consumption, energy efficiency and energy loss varied in the range 18.93–28.15 MJ kg^-1 water, 8.25–13.07% and 16.79–26.01 MJ kg^-1 water, respectively, while the best energy results were obtained at 400 W, 50 °C and 0.5 m s^-1.