Atmospheric Freeze Drying

Abstract

Vacuum freeze drying has been the benchmark technology for making high-quality dried products. This technique, however, is expensive due its high fixed and operating costs. Interest in atmospheric freeze drying (AFD) has increased in recent years as it yields high product quality while reducing the net energy consumption in comparison with vacuum freeze drying. Efforts have been made to overcome some of the limitations of AFD. For example, the required energy for sublimation can be supplied using different modes of heat transfer to enhance the heat transfer rate without compromising quality. A vortex chiller can be used as a suitable alternative to achieve required characteristics of the carrier gas inside the drying chamber. In addition to enhancing the dehydration rate during AFD by improving the external mass transfer coefficient, mixing of the frozen product with adsorbent particles in a vibro-fluidized bed is also examined as an attractive technique. © 2012 John Wiley & Sons Ltd.