How-ever, freeze drying is slow and often low throughput process and also requires expensive equipment.
Because of these reasons, its application is often restricted in producing high-value products (Wang et al., 2011).
The low throughput and long residence time are due to very slow mass and heat transfer rates as the freeze drying process has to be maintained within triple point of water (Duan et al., 2007).
Since freeze-drying is mass transfer controlled process, continuous heating does not accelerate the rate of water removal (George and Datta, 2002).
Therefore, in the conventional freeze drying systems, it is difficult to significantly increase the rate of drying without compromising product quality.
Hence, it would be of practical importance if an alternative freeze drying method with shorter drying time, lower energy consumption and producing desirable product quality is developed.