Prediction of pressure drop through packed beds of granular materials: influence of moisture reduction and air velocity

Abstract The influence of the moisture content of the solids on the pressure drop through packed beds of soy, barley, lentils and oats was investigated. The properties of the grains and the packed beds were determined varying the moisture contents of the solids between the equilibrium moisture content and 0.24 g g-1 (mass of water per mass of dry solid). The pressure drops were measured as a function of the aeration velocity under different moisture contents of the solids. It was observed that a reduction in the moisture content caused a decrease in the particle dimensions but did not affect their shape. Due to the reduction in size caused by the moisture removal, the packed beds become denser and less permeable to the airflow, resulting in an increase in the pressure drop. In the moisture range investigated, the pressure drops increased by more than 39% for lentils, soy and barley, and by about 24% for oats, indicating that the energy consumption during aeration could rise significantly. The parameters of the Forchheimer’s equation were modified to take into account the influence of the moisture content of the solids on the pressure drops. For each particle, empirical equations were proposed and shown to be adequate to accurately predict the pressure drop of the packed beds as a function of the moisture content and aeration velocity.

摘要 本研究考察了固体物料含水率对大豆、大麦、小扁豆与燕麦填充床压降的影响。实验中，通过调节固体物料的含水率（范围为平衡含水率至0.24 g·g⁻¹，即单位干固体的水质量），测定了谷物及填充床的各项特性。研究测定了不同固体含水率条件下，压降随通风速度的变化关系。观测结果表明，含水率降低会导致颗粒尺寸减小，但不会改变颗粒形貌。由于脱湿作用引发颗粒尺寸缩小，填充床会变得更为致密且透气性下降，最终导致压降升高。在本次研究涉及的含水率区间内，小扁豆、大豆及大麦的压降增幅超过39%，燕麦的压降增幅约为24%，这表明通风过程中的能耗可能出现显著提升。本研究对福西海默方程（Forchheimer’s equation）的参数进行修正，以考量固体含水率对填充床压降的影响。针对每种颗粒物料，本研究提出了经验公式，经检验该类公式可准确预测填充床压降随含水率及通风速度的变化关系，拟合效果良好。