云南核桃(Juglans sigillata Dode)对流干燥传质模拟（英文）

Mass Transfer Simulation of Sigillate Walnut(Juglans sigillata Dode) During Convection Drying

在菲克定律与质量守恒定律的基础上建立了模拟云南核桃干燥过程的一维非稳态传质数学模型.通过边界条件的处理,结合云南核桃热风干燥试验,对其干燥过程中内部各层水分分布进行了模拟预测.将含水率的预测值与试验值对比可知该模型与试验数据吻合得很好,试验条件下云南核桃的有效水分扩散系数变化范围为1.14×10^-9-1.73×10^-9m^2/s.干燥初期云南核桃表层的含水率下降速度比内层快得多,之后内层含水率下降速度比表层要快,最终各层含水率稳步下降;从表层到中心,湿度梯度随着干燥时间的增加逐渐减小.分析表明在核桃的干燥过程中,外壳是影响水分扩散的主要阻力之一.该模型有助于云南核桃干燥过程传热传质耦合的研究以及复杂模型的建立.

Based on Fick＇s law and mass conservation law,a numerical model is developed to simulate the unsteady one- dimensional mass transfer during the convection drying process of sigillate walnut in this work.Through boundary condition treatment of diffusion model and combination of experimental drying curves,the effective moisture diffusion coefficients are calculated and the moisture distribution as function of both position and drying time inside sigillate walnut is predicted using numerical calculation. Comparison between the predicted and experimental moisture content shows that the numerical model agrees well with the experimental data. The effective moisture diffusion coefficients vary from 1. 14 ×10^-9to 1. 73 ×10^-9m^2/ s in the conditions studied. During the drying process,moisture content of the surface of sigillate walnut falls much faster than that of internal in the early period,while then the situation is just the reverse,finally the moisture content of each location decreases steadily. The moisture gradients from the surface to the centre decrease as the drying time increase. In addition,simulation results indicate that the shell is one of the most main resistances of moisture transfer during the drying process of sigillate walnut. The model built here is helpful for further study of moisture and temperature distribution as well as the establishment of more complex models of sigillate walnut during drying.