Hybrid and Non-stationary Drying—Process Effectiveness and Products Quality

During last decades a lot of new drying techniques have been developed. Some of them are focused on breaking the limits of convective drying usually by applying intermittent conditions or utilization of few drying techniques in one process (hybrid drying). The purpose of the chapter is to discuss these new opportunities. Hence the convective non-stationary drying and various hybrid drying techniques (convective–microwave, convective–microwave–infrared, convective–microwave–ultrasonic and microwave-vacuum drying) are discussed. Many examples are provided in this chapter to illustrate the impact of the applied drying conditions and techniques on time consumption, process energy consumption, and on the quality of the product obtained. In particular, the drying of kaolin clay, oak, pine and walnut wood, apple, carrots, kale, potatoes, raspberries and red pepper are presented. The results of the studies indicate that both variable drying conditions and hybrid techniques may result in improved drying kinetics, reduced process energy consumption, and increased product quality.