Exergy analysis of freeze-drying process

In this paper, the energy utilization in freeze-drying process is studied. As a complicated process with coupled mass and heat transfer, the freeze-drying process is decomposed of several sub-processes. By the conservation equations of mass, energy, and exergy, mathematical expressions of every stage in freeze-drying process are established. The exergy of each state and exergy losses of any period are determined. Exergy analysis, based on the second law of thermodynamics, is utilized to analyse freeze-drying processes in this study. At the same time, operating conditions affecting the exergy losses and sublimate drying time are also analyzed, including temperature differences of refrigeration and heating, and the pressure of drying and of the cold sink. The methods to reduce the exergy losses are pointed out in the paper.