丝状颗粒在滚筒横向截面中的传热传质特性

Heat and mass transfer characteristics of filamentous particles in transverse section of rotary dryer

针对丝状物料在滚筒内干燥不均等问题,从干燥机理出发,建立了一种基于离散单元法的丝状颗粒传热传质数学模型.利用该模型对滚筒横向截面中丝状物料的温度和含水率的变化过程进行了分析计算,并通过实验验证了数学模型的有效性.研究结果表明:筒壁温度的变化对丝状颗粒传热传质特性有着直接且重要的影响;在干燥的初始阶段,颗粒彼此间温度的不均匀性迅速增大,但随着干燥的进行,颗粒之间的温度差别又呈现出逐渐缩小的趋势.颗粒间含水率的不均匀性在干燥的初始阶段同样迅速增大,当满足一定的干燥条件或一定的干燥时间,筒体内部丝状颗粒的干燥程度将会越来越均匀;丝状颗粒在滚筒中所获取的热量主要来自于与高温壁面(特别是与筒体之间)的接触导热;与升举式抄板相比,均布式抄板可使颗粒在滚筒横截面上的分布及颗粒间的温度和含水率更加均匀.

On account of drying inequality problem of filamentous materials in the rotary, a mathe-matical model for heat and mass transfer of filamentous particles based on the discrete element meth-od was proposed according to drying mechanisms, and then it was used to numerically study the tem-perature and moisture content evolution of filamentous materials in the transverse section of a rotary dryer.The effectivity of this model was verified by experiments.The results show that the change of the temperature of the cylinder wall has a direct and significant impact on the heat and mass transfer characteristics of filamentous particles.At the initial stage of drying, the standard deviation of the particles temperature increases rapidly, but then it reduces gradually with the dying time.And the standard deviation of the moisture content also increases rapidly at the initial stage of drying.When the certain drying conditions or the drying time is met, the uniformity of moisture content of filamen-tous particles inside the cylinder will be better and better.The heat flux of filamentous particles mainly obtains from the high temperature wall, especially from the cylinder wall.Compared with the lifting type baffle, the uniform type baffle can make the temperature distribution and the moisture content distribution of the particles on the transverse section of the cylinder more uniform.