非固结多孔介质干燥的双尺度孔道网络模型与模拟

DUAL-SCALE PORE NETWORK SIMULATION ON DRYING OF UNCONSOLIDATED POROUS MEDIA

以农产品颗粒物料中常见孔隙直径范围(10^(-4)～10^(-3) m)的非固结多孔介质为研究对象,运用孔道网络方法和传递过程原理等知识,建立了考虑骨架吸湿、汽相对流、温度梯度和孔道结构特征等因素对干燥过程影响的非固结多孔介质双尺度孔道网络干燥模型,并进行了相应的干燥实验.模拟与实验结果表明:该模型可有效模拟非固结多孔介质的干燥过程;非固结多孔介质的孔隙率、直径(包括粒径与孔径)分布对干燥的影响十分显著,孔隙率越大,物料干燥越快,达到相同湿含量干燥所需时间越短;直径分布的不均匀程度越高,干燥所需时间越长,物料湿含量分布的差异也越大。对于窄筛分农产品颗粒物料,进行干燥计算时可以采用同一直径分布代替实际分布.

Taking the unconsolidated porous media with common pore diameter range（10^-4～10^-3 m） in grain material of farm produce as study object,applying the theories of drainage and percolation through porous media and transport-process,a dual-scale pore network model for unconsolidated porous media drying was developed.Various factors for the drying process,such as sketch hygroscopicity,vapor-phase convection,temperature gradient,as well as physical structure characteristic were considered into this model.The experiment and simulation results indicate that the dual-scale pore network model could explain the drying process of unconsolidated porous media well.The parameters of porosity and distribution law（included the pore and particle size） have a great effect on the drying process.The greater the porosity was,the faster the material would be dried.The higher the uneven degree of size distribution was,the longer the drying time and the more unbalanced the moisture distribution of material.The real size distribution of the commonly grain materials screened narrowly could be replaced by the same size distribution when the drying parameters were calculated.