Abstract

Freeze-drying is an effective method for aortal preservation. However, there are few studies on heat and mass transfer of aortal freeze-drying. In this study, the contactless weighing device was used to monitor freeze-drying process. The radiation view factor of the aortal segment was estimated, and the quasi-steady state model was used to analyze heat and mass transfer, there was a certain amount of heat flux in the frozen layer, which provided sublimation heat for internal sublimation interface. By theoretical calculation, the vapor diffusion coefficient was determined. The unsteady state model was used for numerical simulation. The simulated result of free water removal ratio was consistent with experiment result. Both heat flux density and mass flux density decreased non-linearly in the early stage, but approximately linearly in the late stage. The velocity of inner and outer sublimation interfaces was almost the same. The nodes temperature gradually increased and finally approached the heating temperature, and the temperature gradient of both dried and frozen layers decreased gradually with drying time. The water vapor pressure gradient was smaller near the aortal wall and larger in the middle region.

摘要

冷冻干燥是一种有效的主动脉保存方法。然而，关于主动脉冷冻干燥传热传质的研究较少。在这项研究中，非接触式称重装置用于监测冷冻干燥过程。估算了主动脉段的辐射视角因子，采用准稳态模型分析传热传质，冻结层存在一定的热通量，为内部升华界面提供升华热量。通过理论计算，确定了蒸汽扩散系数。非稳态模型用于数值模拟。游离水去除率的模拟结果与实验结果一致。热通量密度和质量通量密度在早期均呈非线性下降，而在后期则近似呈线性下降。内外升华界面的速度几乎相同。节点温度逐渐升高，最终接近加热温度，干燥层和冷冻层的温度梯度随着干燥时间的推移逐渐减小。主动脉壁附近水蒸气压梯度较小，中部水蒸气压梯度较大。