Micro-CT scanner was used to follow the moving interface during sublimation. Apples slices used as experimental samples were scanned at certain time when drying. The scanning images were analyzed, then variation curves of grey value were obtained. To different thicknesses?￠freezing rates and primary drying temperatures, the different sublimation phenomena were compared. The results show that heat and mass exchange occurs both at the upper and the under surface of the sample. Also the exchange occurs at the side surface to some extent. To thick samples, the interface showing as a three-dimensional moving mode contracts to the geometric centre of the sample and presents approximate globosity. Samples frozen of slow freezing sublimate more quickly than those of quick freezing. The higher the primary drying temperature is, the more quickly sublimation interface moves. However, samples shrink and collapse more severely with high drying temperature under quick freezing condition.
展开▼
