多孔介质对流干燥过程数值模拟

Numerical simulation of porous media convective drying

为研究含湿毛细孔介质干燥过程的相变现象,建立了相变的传热传质数学模型.模型中以残余饱和度将多孔介质划分为湿区与干区,湿区和干区以“蒸发界面”动态边界相互耦合.用有限差分方法对多孔介质一维干燥过程进行了计算,数值解表明:干区是等速干燥与降速干燥的分界点;干燥初期多孔介质压力升高,温度下降;随后在等速干燥段温度分布保持不变,在出现干区时再度升高.干区出现的初期,蒸发界面向多孔介质内部推进的速度较慢,在到达介质厚度10%左右时出现转折,随后推进速度加快.

In order to study the phase change phenomena of wet capillary porous media during drying, a model of heat and mass transfer with phase change was established. In the model, porous media were separated into two regions： the wet region and the dry region according to the irreducible saturation, and two regions were coupled by a dynamic evaporation front boundary. The finite difference method was used to solve the problem of the model for a one-dimensional drying process.Numerical results show that the appearance of the dry region is the critical point between constant drying rate period and fall drying rate period. At the beginning of drying, porous media surface is heated, pressure in porous media increases while temperature decreases. The temperature keeps constant during constant drying rate period while it increases when the dry region appears. The evaporation front interface moves slowly in the initial stage of dry region appearing, and then it advances quickly when it breaks through 10％ thickness of porous media.