Quantitative investigation on the effects of ice crystal size on freeze-drying: The primary drying step

Abstract

The size of ice crystals formed in the freezing process has a significant impact on the subsequent primary drying process. However, the effects have not been fully understood. The purpose of this study was to quantitatively investigate the effects of ice crystal size on water vapor concentration, temperature, and primary drying time. A mathematical model considering the effects of ice crystals size was proposed, and it was solved by Comsol Multiphysics. Results show that there is less water vapor in the products with larger ice crystals. Temperature is found to decrease initially, and larger ice crystals lead to a higher temperature in the dried zone while the lower temperature in the frozen zone. The primary drying process proceeds faster when the ice crystal size is large, and the decrement of primary drying time gets smaller when further increasing the size of ice crystals. This work could provide help for the optimization of freeze-drying.

Keywords:

• Freeze-drying
• primary drying
• controlled nucleation
• ice crystal size

Disclosure of interest statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work is supported financially by the National Science Foundation of China (No. 51676209), the Fundamental Research Funds for the Central Universities of Central South University (2020zzts468).