Pore network modeling of freeze drying on the basis of lyomicroscopic and tomographic measurements

冷冻干燥是制造高价值产品的必要和常见工艺，但它也缓慢且昂贵。努力提高效率推动过程进入区域，其中产品的固体支架可以软化和崩溃。这样的破坏性事件总是局部的，因此不能被传统的连续统模型捕捉到，否则它们的预测能力也会受到限制。因此，本课题将首次建立一个能够代表微观尺度的孔隙网络模型用于冷冻干燥。孔隙网络将是三维的、不规则的。它将考虑热量和质量传递的局部、孔隙尺度变化以及干燥体的结构和性质，热传递与干燥之间存在双向耦合。冷冻实验和后续糖水溶液在lyom显微镜下的冷冻干燥实验将指导模型的开发。冷冻是至关重要的一步，因为它会在周围形成不同大小和形状的冰晶，然后将其干燥。冷冻或冻干材料的形态在三维x射线断层扫描数据的基础上进行评估，并用于生成真实的孔隙网络。对孔隙网络模型的参数进行了识别，并在导致结构坍塌的条件区域内外进行了冻干试验，对模型进行了验证。

Freeze drying is a necessary and common process in the manufacturing of high-value products, but it is also slow and expensive. Efforts to increase the efficiency push the process into regions, in which the solid scaffold of the product can soften and collapse. Such damaging events are always local and can thus not be captured by conventional continuum models, which are also otherwise limited in their predictive ability. Therefore, and for the first time, a pore network model capable of representing the microscale shall be developed for freeze drying in this project. The pore network will be three-dimensional and irregular. It will account for the local, pore-scale variation of heat and mass transport as well as of structure and properties of the drying body, with two-way coupling between heat transport and drying. Freezing experiments and experiments of subsequent freeze drying of aqueous sugar solutions in a lyomicroscope will guide model development. Freezing is a crucial step, because it creates around ice crystals of different size and shape the solid scaffold to be subsequently dried. The morphology of the frozen or freeze dried material is evaluated on the basis of three-dimensional X-ray tomography data and used to generate realistic pore networks. Parameters of the pore network model are identified and the model is validated by freeze drying experiments conducted both outside and within the region of conditions that result in structural collapse.