【作者】 罗华俊；

【导师】 陈庚；

【作者基本信息】 北京交通大学 ， 工程热物理， 2011， 硕士

【摘要】 干燥过程是城市生活垃圾焚烧前的必经阶段,干燥的好坏直接决定了焚烧的效率。由于城市生活垃圾是一种高含湿量的多孔介质物料,干燥过程中往往发生严重的收缩。因此,本文主要就热风干燥条件下收缩性垃圾基元内部热质传递规律开展研究。通过在热风对流干燥实验台上进行垃圾基元的实验研究,得到温度、风速、垃圾基元种类及其几何因子对基元湿分迁移特性的影响规律以及基元干燥收缩特性的变化规律,结果表明收缩率与失重率之间呈现线性关系(R2>0.95),基元减少的体积近似地等于基元脱出的水分的体积。对正交实验结果进行了极差与方差分析,发现温度、风速及基元失重率对收缩率影响显著(a=0.05)；温度及基元厚度对干燥时间影响显著(a=0.05)。基于Fick定律及能量守恒方程建立数学模型。通过MATLAB平台编写计算程序,采用隐式格式有限差分法计算得到基元内部湿分分布与温度分布,发现对流边界含湿量与温度呈现阶跃式的变化特征。通过模拟与实验对比得到平均有效湿分扩散系数为温度与含湿量的递增函数,范围为3.245×10-20.576×10-8m2/s。对基元干燥过程进行了动力学分析,整理出基元的Arrhenius方程,在本文研究条件下基元表观活化能为10-22kJ。对干燥控制方程进行无量纲化重写与级数分析得到了垃圾基元内部热质传递规律。基元传热毕渥数Bi与传质毕渥数Bim级数为100-101之间,说明在干燥过程中,热质传递都是由内部控制的导热与湿分扩散过程,说明垃圾基元的内部传热传质特性受外界干燥条件(热风风速,热风相对湿度)的影响较小,而主要在于基元自身的热物理特性。在本文所研究的干燥条件下,垃圾基元表面传热系数为9.5-184.5W/(m2·K)；传质系数为：6.2×10-6-7.4×10-4m/s。更多还原

【Abstract】 Drying process is the neccessary stage before the Municipal Solid Waste (MSW) incineration and its combustion efficiency is mainly determined by the quality of dry process. Serious contraction occurred in the consideration of MSW is a kind of porous materials which has the high moisture content. For this reason, this paper focus on the internal heat and mass transfer characteristic of shrinkable MSW matrixes during hot air convection drying.The hot air convection drying experimental study of the MSW matrixes has been carried out and the influence rules of moisture migration characteristic by hot air tempertature, windspeed, matrixes kinds and geometric factor were obtained. Also, the shrinkage characteristic was obtained. Result shows the linear relationship between shrinkage factor and weight loss ratio (R2>0.95), the MSW matrixes volume reduced was approximately equal to the volume of water loss. Through the orthogonal experimental results of range and variance analysis, it shows that temperature, windspeed and weight loss ratio has significant effect on the shrinkage factor (α=0.05),the temperature and thickness has significant effect on drying time.Based on the Fick law and energy conservation equation, the mathematical model has been built. Calculating programme has been designed base on the MATLAB, through the implicit finite difference method, the internal temperature and moisture distribution were obtained, moisture content and temperature on the convection boundary shows the step-like changes. Through the comparison between experimental value and calculating value found that average effective moisture diffusivity was an increasing function about moisture content and temperature, value range is 3.245×10-8～20.576×10-8m2/s. Throught the dynamic analysis, the Arrhenius equations were obtained. Under conditions in this study, the apparent activation energy range is 10～22kJ.After dimensionless rewrite about the governing equation and series analysis, law of internal heat and mass transfer were obtained. Bi and Bim series were 100～101, it shows that heat and mass transfer were governed by the internal conduction and diffusion, external drying conditions (hot air velocity and relative humidityof dring air) has limit affect about internal heat and mass transfer process. Under conditions of this study, surface heat transfer coefficient of matrixes is 9.5～184.5W/(m2·K) and surface mass transfer coefficient of matrixes is 6.2×10-6～7.4×10-4m/s.更多还原