具有预制孔隙多孔介质冷冻干燥的多相传递模型

摘要

基于局部质量非平衡假设,建立了多相多孔介质热、质耦合传递数学模型,理论验证具有预制孔隙的初始非饱和多孔物料对冷冻干燥过程的强化作用.模型考虑了多孔介质的吸湿效应,构建了3种吸附-解吸平衡关系.模型使用基于有限元法的COMSOL Multiphysics软件平台数值求解,并与实验数据进行了比较.结果表明,初始非饱和冷冻物料能够有效地强化冷冻干燥过程.采用不同函数形式的吸附-解吸平衡关系模拟的干燥曲线均与实验数据非常吻合.通过分析物料内部的饱和度、温度和质量源分布,探讨了初始非饱和物料冷冻干燥过程的传热传质机理.初始非饱和物料的干燥速率控制因素主要是传热.模拟考察环境辐射温度对冷冻干燥过程影响的结果表明,所建模型具有良好的预测能力.%Based on the hypothesis of the local mass non-equilibrium, a multiphase porous media drying model of heat and mass transfer was developed to verify the effect of porous frozen materials with prefabricated porosity on freeze-drying. Three kinds of adsorption-desorption equilibrium relationships were constructed to express the hygroscopic effect of moist porous media. The model was solved numerically on the commercial software platform of COMSOL Multiphysics based on the finite element method. Results showed that the freeze-drying process can be effectively enhanced with the initially unsaturated material. Excellent agreements were achieved between model simulative results and experimental data using the three kinds of the proposed adsorption-desorption equilibrium relationships. The different relationships can be unified into a Taylor polynomial through Taylor extensions of some elementary functions. Heat and mass transfer mechanism was discussed according to temperature, saturation and mass source profiles. The drying rate-controlling factor is mainly heat transfer for the initially unsaturated material. Numerical examination of the ambient temperature effect on the freeze-drying process illustrated that the developed model provided good prediction capacities.