Intermittent and continuous drying of foods in a developed microwave-convective hybrid dryer

Growing concerns about the quality as well as cost of production has boosted the researchers to select the combined drying techniques. Due to several advantages such as shorter drying time, enhanced product quality, and reduction in energy consumption, hybrid drying opens up new possibilities to develop novel drying technologies. To overcome the operational difficulties encountered in conventional dryers and to improve the quality of the dried products, a microwave-convective hybrid dryer -in which both hot air and microwave drying take part simultaneously- has been constructed for drying foods. Experiments were conducted for hot air drying, microwave drying, and hybrid drying, respectively for both intermittent and continuous drying of the pomegranate arils. The effects of air temperature and the microwave power on the drying kinetics were investigated. The most suitable mathematical model was selected for the microwave-convective drying kinetics of the pomegranate arils. So as to investigate the effects of the microwave power and air temperature on hybrid drying kinetics of pomegranate arils, microwave drying experiments of pomegranate arils were conducted for 140, 294 and 364 W microwave power levels, hot-air drying experiments were conducted for 40, 50, 60 and 70 °C air temperature at constant velocity and hybrid drying experiments were conducted for the combination of these drying conditions for continuous and intermittent drying. Microwave, convective and hybrid drying kinetics of pomegranate arils were investigated drawing the moisture content-drying time, drying rate- drying time and drying rate-moisture content drying curves. No constant rate period has been observed. Drying took place in the falling rate period. Mathematical modeling of thin layer drying kinetics of pomegranate arils under hybrid treatment was also investigated by fitting the experimental drying data to frequently used thin layer drying models in the literature. Since Henderson and Pabis model had very high R2 and very low χ2 and RMSE values for three drying procedures among the thin layer drying models proposed, Henderson and Pabis mathematical model was determined as the appropriate thin layer drying model.