Abstract: The distribution of particle packing in fixed beds, influenced by wall effects, has been extensively researched, however, the impact of this distribution on heat transfer characteristics has been less studied. This study aims to investigate the specific effects of wall effects on heat transfer properties by utilizing discrete element method simulation to analyze the radial voidage distribution, particle coordination number, and the contact conditions between particles and the wall within the fixed bed. These data are then applied to Eulerian simulations to investigate their impact on the bed's heat transfer performance. The discrete element method simulation results reveal that wall effects significantly influence the radial voidage distribution and particle coordination number within the fixed bed. Notably, only about 10% of the particles in the layer adjacent to the wall are in direct contact with it, a finding that is crucial for understanding the heat transfer mechanism. The Eulerian simulation study indicates that wall effects have a significant impact on the rate of temperature rise within a range of one particle diameter from the wall. However, under the current parameter settings, the radial voidage distribution and particle coordination number have a relatively minor impact on the bed's temperature increase rate. By accounting for the thermal resistance in the near-wall region or by adjusting the model to reflect the particle-wall contact ratio, a more accurate prediction of the bed's temperature increase can be made, thereby improving the understanding of the heat transfer process in fixed beds subject to wall effects. Compared to the thermal resistance model, incorporating the contact ratio between the wall and adjacent particles not only maintains calculation accuracy but also improves computational efficiency. This approach is crucial for the heat transfer simulation of industrial-scale fixed beds and can provide important guidance and assistance for the design and optimization of industrial-scale reactors.

Key words: near-wall effect, effective thermal conductivity, particle-wall contact condition, Eulerian simulation, discrete element method

摘要： 固定床中颗粒堆积分布受壁面效应的影响已有广泛研究，但关于其对传热特性的影响则研究较少。本研究旨在深入探讨壁面效应对传热特性的具体作用，通过离散单元法模拟固定床内部的径向空隙率分布、颗粒配位数以及颗粒与壁面间的接触状况，并将这些数据应用于欧拉模拟中，以考察它们对床层传热性能的影响。离散单元法模拟结果表明，壁面效应对固定床内部的径向空隙率分布和颗粒配位数有显著影响。紧邻壁面的颗粒层中，仅有约10%的颗粒与壁面直接接触，这一发现对理解热传递机制极为关键。欧拉模拟研究表明，壁面效应对距离壁面1个颗粒直径范围内的温度上升速率有显著影响。尽管如此，在目前的参数配置下，径向空隙率分布和颗粒配位数对床层升温速率的影响相对较小。通过考虑近壁区域热阻或者调整模型以反映颗粒与壁面的接触比例，可以更准确地预测床层升温情况，从而提高对受壁面效应影响的固定床热传递过程的理解。与热阻模型相比，引入壁面与相邻颗粒之间的接触比不仅保持了计算的精确性，而且还提高了计算效率。这种方法对于工业规模固定床的传热模拟至关重要，可为工业规模反应器的设计和优化提供重要指导。

关键词: 近壁效应, 有效导热系数, 颗粒-壁面接触情况, 欧拉模拟, 离散单元法