Multi-objective optimization of savory leaves drying in continuous infrared-hot air dryer by response surface methodology and desirability function

Abstract

Drying process of savory leaves was optimized in conveyer-belt infrared-hot air dryer using response surface methodology and desirability function. Effect of air temperature (40–60 °C), air velocity (0.5–1.5 m/s) and infrared power density (0.181–0.253 W/cm2) investigated on drying time, moisture removal rate (MRR), specific energy consumption (Esc) and quality parameters. Drying time varied between 26.0 and 53.9 min. Specific energy consumption increased with increasing temperature and air velocity and decreasing of infrared power. The MRR varied between 0.193 and 0.398 kg water/h. Color change (ΔE) increased with increasing drying temperature and air velocity at high levels of infrared power density (0.253 W/cm2) and decreased at low infrared power density (0.181 W/cm2). The air velocity had no significant effect on the rehydration ratio (RR) of dried samples. Optimization of the drying parameters for the given constraints resulted in 40 °C, 0.53 m/s and 0.250 W/cm2. At this optimum condition, the values of experimental test were found to be 14.05 (ΔE), 2.94 (RR), 10.50 MJ/kg water (Esc), 29.83 min (drying time) and 0.350 kg water/h (MRR), respectively, with desirability factor of 0.810.