In this study

the contactless weighting method was used to monitor the freeze-drying process of porcine aortas

and the dehydration rate was obtained in real time. For the sublimation drying process

the quasi-steady heat transfer model combined with the change in the dehydration rate could be used to calculate the change law of sublimation temperature

sublimation interface displacement

and heat transfer on each surface. The freeze-drying parameters were set as follows: the pre-freezing temperature was ?40 ℃

the primary drying temperature was ?20 ℃

the secondary drying temperature was 10 ℃

and the pressure of the freeze-drying chamber was 10 Pa. The study showed that the average moisture content of the sample was 74.24%

and the free water content was 71.96%. During the primary drying

the sublimation temperature increased slowly and eventually approached the shelf temperature. As the heat transfer temperature difference decreased

the heat transfer decreased rapidly

and the removal rate of free water decreased gradually. The sublimation of ice crystals was mainly concentrated in the inner and outer walls of the blood vessels

and its heat transfer accounted for 70%–90% of the total sublimation heat. With the decrease in heat transfer

the moving velocity of the sublimation interface decreased gradually. During the early stage of sublimation drying

the mass transfer resistance increased at a constant rate with the thickness of the dried layer

whereas during the later stage

the increasing rate of mass transfer resistance increased significantly with the restriction of the heat transfer.