ABSTRACT

In this study the thermo-physical and mechanical properties of an industrial sludge like shrinkage coefficient, density, water activity, apparent moisture diffusivity, effective thermal conductivity and heat capacity are determined experimentally. These properties constitute a major part of the required input data to model the sludge drying. The sludge shrinks linearly until reaching a critical water content X_cr = 23% and then maintains a constant volume until the end of drying. Therefore, the density increases with decreasing the water content until the critical value (X_cr = 23%) then it decreases until the end of drying. The Henderson equation seems to be the most appropriate statistical model to describe the water sorption isotherm of the sludge. The apparent moisture diffusivity is determined from the numerical solution of Richard’s law of diffusion with shrinkage. The results show that the effective thermal conductivity and the heat capacity decrease with the reduction of the water content from 2.60 W m⁻¹ K⁻¹ and 2.52 J g⁻¹ K⁻¹ for a wet sludge to 1.71 W m⁻¹ K⁻¹ and 0.78 J g⁻¹ K⁻¹ for a dry sludge respectively. The relationships between thermo-physical / mechanical properties and the water content / temperature of the sludge are established to be introduced in the created numerical drying model.

摘要

在这项研究中，工业污泥的热物理和机械性能，如收缩系数、密度、水分活度、表观水分扩散率、有效热导率和热容量是通过实验确定的。这些属性构成了模拟污泥干燥所需的输入数据的主要部分。污泥线性收缩直至达到临界含水量Xcr = 23 _%  ，然后保持恒定体积直至干燥结束。因此，密度随着含水量的降低而增加，直到临界值（X _cr = 23%) 然后它会减少直到干燥结束。Henderson 方程似乎是描述污泥吸水等温线的最合适的统计模型。表观水分扩散率由 Richard 的收缩扩散定律的数值解确定。结果表明，随着含水量从湿污泥的 2.60 W m ^-1  K ^-1和 2.52 J g ^-1 K ^-1降低到 1.71 W m ^-1 K ^{- ，有效热导率和热容降低。 1}和0.78 J g ^-1 K ^-1分别为干污泥。建立了污泥的热物理/机械性能与含水量/温度之间的关系，以将其引入所创建的数值干燥模型中。