Heat and Mass Transfer in Packed Beds Accompanied by Exothermic/Endothermic Reactions

对13X沸石和硅胶A吸附水蒸气的薄层填充床内的传热传质进行了实验和数值分析。此外，还测量了床层的有效导热系数。吸附速率一般随着床层厚度的增加而减小，在吸附速率较高的沸石床层中，吸附速率随颗粒尺寸的减小而减小。这些减少主要归因于床层内的热传导阻力和颗粒间隙中的传质阻力，特别是在吸附初期。存在一个最佳床层厚度，在该厚度处单位换热面积的吸附水量最大，这是因为它取决于吸附速率和填充的吸附剂的量。在固定床中，吸附速率在吸附期的后半段有所提高。吸附速率可用单一的无量纲方程表示，与吸附剂种类、颗粒大小、床层厚度和床层类型无关。考虑水蒸气吸附引起的颗粒导热系数升高，吸附填料床的有效导热系数可用S模型和鲍尔-施伦德模型进行较好的预测。3.固定在翅片侧面的床内的吸附速率可通过考虑翅片段内的导热效应来估算。4.基于考虑床内发生的基本过程的物理模型，对吸附蒸汽的填充床内的传热传质进行了数值分析，计算结果与实验结果吻合较好。

Experiments and numerical analyses were made on heat and mass transfer in thin packed beds of zeolite 13X and silica gel A adsorbing steam. In addition, the effective thermal conductivity was measured for the beds.1. The adsorption rate generally decreases as the bed thickness increases, and it reduces with the decrease of grain size in the zeolite bed where the adsorption rate is high. These reductions are attributed mainly to the resistance to heat conduction within the bed and more or less to the resistance to mass transfer in the interstices of grains especially in the early stage of the adsorption period. There is an optimum bed thickness at which the amount of adsorbed water per unit area of heat transfer surface takes a maximum, because it depends on both the adsorption rate and the amount of packed adsorbent. In the consolidated bed, the adsorption rate is enhanced in the latter half of the adsorption period. The adsorption rates can be expressed by a single non-dimensional equation, irrespective of kinds of adsorbent, grain size, bed thickness and types of bed.2. The effective thermal conductivity of the adsorbent packed bed can be predicted well by both the Hayashi et al.'s model and Bauer-Schlunder model, by considering the particle thermal conductivity rise due to the steam adsorption.3. The adsorption rate in the bed fixed on the side surfaces of a fin can be evaluated by considering the effect of heat conduction within the fin segment.4. Numerical analyses were made on heat and mass transfer in packed beds adsorbing steam, based on a physical model taking account of elemental processes which take place in the bed. Calculations of the adsorption rate were in good agreement with measurements.