吸湿多孔介质冷冻干燥传质传热模型

本研究在作者提出的吸附—解吸平衡关系的基础上,建立了一个全新的考虑吸湿效应的多孔介质冷冻干燥数学模型。模型用有限差分法进行求解,并带有一个移动边界,以模拟介电材料辅助的微波冷冻干燥过程。介电材料选用碳化硅（SiC）,原料液为脱脂奶。模拟结果表明：介电材料能够有效强化微波冷冻干燥过程。在典型操作条件下,介电材料辅助的微波冷冻干燥所用的时间比普通微波冷冻干燥减少33.1%。当料液中固体含量较低或者固体产品的损耗因子较小时,介电材料对微波加热的效果不明显。基于冰饱和度、温度和水蒸气浓度的分布,本文分析了干燥过程中的传质传热机理,并对干燥速率控制因素进行了讨论。

Heat and Mass Transfer Model of Hygroscopic Porous Media on Freeze-Drying

A novel mathematical model of porous media on freeze-drying was developed based on the adsorption-desorption relationship proposed in this work. A finite difference solution was obtained with a moving boundary for the dielectric-material-assisted microwave freeze-drying process. Sintered silicon carbide （SIC） was selected as the dielectric material and skim milk was used in preparing the aqueous solution to be dried. Simulation results show that the microwave freeze-drying process can be significantly enhanced with the dielectric material. The drying time is 33.1% shorter than that of ordinary microwave freeze-drying under typical operating conditions examined. When the solid content in solution is very low or the solid product has a very small loss factor, microwave heating is less helpful without assistance of the dielectric material. Based on distributions of ice saturation, temperature and vapor concentration, mechanisms of heat and mass transfer during drying were analyzed and drying rate-controlling factors were discussed.