血管冻干工艺过程中升华界面移动特性的微CT实验

背景：前期实验发现冻干过程中物料内部的孔隙分部、空隙连通度等对内部传热传质影响较大，但对于干燥过程热质迁移的机制未阐明。 目的：在前期实验基础上，以微CT为分析工具，尝试对冷冻干燥过程中升华界面移动特性进行实验观察分析，希望对血管冻干工艺提供参考。 方法：以新鲜猪主动脉为材料使用微CT扫描仪的扫描成像、图像重构及灰度值分析技术对血管在冻干时升华过程进行观察分析。 结果与结论：冻干温度曲线斜率初期较大，升华速率较快，由血管的二维横截面重构图像中可以看出冻干区与冰晶区的灰度值差别较大，升华界面明显，升华是在物料的外表面和内表面同时进行，界面移动明显。随着时间推移，温度曲线斜率变小，升华速率也随之变慢，界面移动逐渐不明显。对于竖直放置的血管在底部进行加热的干燥过程，升华是在外表面和内表面同时进行的。升华界面逐渐向血管壁面中心移动。冻干过程随时间推移热质传递阻力增大，升华速率减慢。

Micro-CT experimental study concerning movement characteristics of sublimation interface in freeze-drying preservation of the artery

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.