流化颗粒表面喷雾冷冻干燥典型食品料液的机理研究

Spray freeze drying (SFD) is a new technique to produce dispersible powders, which is of great significance to the preparation of high value-added functional materials, pharmaceutics, and foods, etc. But the present SFD processes have some disadvantages, such as difficulties in processing fine powders, lower efficiency in heat and mass transfer, and lower productivity. With respect to these points, a novel SFD technology has been proposed, i.e., the atomized droplets are coated on the cold surfaces of fluidized particulate carriers, then frozen, dried, and finally separated from the carriers as powder product. In this project, we focus on some typical materials of high viscosity, volatility or biologically active substances to study the process principles. We will comprehensively study the phenomena of droplet-surface interactions, spray-freeze droplets coating on the fluidized particles, and freeze drying of composite particles in fluidized beds. Design of experiments and mathematical modeling will be carried out to deal with the multi-physical mechanisms of cold coating and freeze drying in fluidization with advanced measurement technologies. Droplet impact mechanics and freezing mechanisms are elucidated. The spray-freeze coating process as well as drying kinetics on particulate carriers in fluidized bed is investigated via mathematical modeling and real-time measurements. On the other hand, the coating morphology and product quality is analyzed at micro-scale. Consequently, the optimal process parameters will be obtained for three typical food solutions with the nature between product properties and operational conditions to be known, which is essential to apply this drying technology to practically process food solutions.

喷雾冷冻干燥提供了一种生产分散性粉体的工艺过程，对制备高附加值的药物、功能材料、食品等具有重要意义。本项目针对目前喷雾冷冻干燥过程中操作性差、传热传质效率低、产量低等问题，提出一种新的喷雾冷冻干燥方法，即将雾化的液滴涂敷在流化的冷载体颗粒表面，料液经喷敷、冻结、冷冻干燥、剥离过程形成粉体产品。针对高黏度及含有易挥发物质或生物活性物质的代表性食品料液，研究其过程机理。主要研究内容为单液滴撞击冷球形表面的动力学行为，载体流化床颗粒表面料液喷覆、冻结以及流化床冷冻干燥。运用实验设计方法和数学模拟、先进的测试技术，研究冷涂覆、干燥的多物理场耦合现象，解明颗粒动力学、料液冻结相变机理，把握流化状态下载体颗粒表面喷雾冷冻涂覆及干燥过程机理，并对冷涂覆层及产品性质进行微观分析，得出三类食品料液喷雾冷冻干燥的优化条件以及操作条件、料液特性对产品品质影响的内在关系，为该技术在食品加工应用提供理论基础。

本项目以流化颗粒表面喷雾冷冻干燥食品料液中的流化、喷雾、涂覆、冻结、干燥过程为研究对象，运用实验设计方法和数学模拟、先进的测试技术，从宏观、介观、微观三个层面探究了载体颗粒喷雾冷冻干燥粉体产品的形成过程与机理。研究了冷涂覆、干燥的多物理场耦合现象，研究了料液形成的液滴与载体颗粒的接触碰撞现象、干燥过程、以及产品品质特性，并对冷涂覆层及产品性质进行微观分析，得出了食品料液喷雾冷冻干燥的优化条件以及操作条件、料液特性对产品品质影响的内在关系。进行了单液滴撞击低温表面的涂覆效果实验，研究了不同速度的单液滴撞击不同温度、不同倾斜角度、不同材质、不同纹理的板面时，液滴的形状、尺寸和冻结形态的变化，建立了描述液滴铺展过程及在冷板面上固化的数学模型，建立了液滴铺展的二维与三维物理模型，解明了料液冻结相变机理。进行了微米级液滴群涂覆低温静态颗粒群的实验，研究液滴束涂覆低温颗粒群过程中涂覆面积及厚度变化情况，提出了控制液滴涂覆的准则并得出了回归方程，解明了“液滴—载体颗粒”冷涂覆机理。研制了应用于大颗粒流态化的压降可调节式均匀布风系统，并自主设计了用于布风系统的可调狭缝型分布板，设计制造了喷雾冷冻干燥一体机和应用于惰性颗粒流态化冷冻干燥的喷动床喷雾冷冻干燥设备，研究了惰性粒子的大小对喷雾冷冻干燥时间和所得奶粉性能的影响，从微观角度研究了喷雾冷冻干燥过程对干燥粉体形态学的影响机制，建立了载体颗粒表面冷涂敷过程（表现在冻结料液层结构特征）与最终产品特性之间的关系。