Abstract:

BACKGROUND: Previous studies demonstrated that freeze-drying had great influence on internal heat transfer, such as pore distribution and void connectivity, however, the mechanisms involved in heat and mass transfer during drying is poorly understood.
OBJECTIVE: Based on the previous studies, micro CT was served as analytical tool, to observe the movement characteristics of sublimation interface in freeze-drying process. 
METHODS: With aorta of pig, micro-CT scanning, image reconstruction and the technique of grey value analysis were used to observe and analyze the sublimation process in freeze-drying.
RESULTS AND CONCLUSION: The slope of freeze-drying temperature curve was large at first, causing quick sublimation rate. The grey value of freeze-drying and ice crystal area was very different in second-dimensional cross-sectional reconstructed image. Sublimation interface was clear and sublimation took place simultaneously both in the outer surface and inner surface. The movement of sublimation interface was obvious at this time. Along with the time, the slope of freeze-drying temperature curve became small, leading to slow sublimation rate. The movement of sublimation interface turned unclearly.
For the vertically placed artery, when heated at the bottom, the sublimation takes place both in the outer surface and inner surface at the same time. The sublimation interface slowly approaches to the middle of vessel wall. With time prolonged, resistance for heat and mass transfer in freeze-drying is increased, and the sublimation rate becomes slowly.