In this study, two randomly packed beds with small tube-to-particle diameter (D/d) ratios of D/d = 4 (PB-4) and D/d = 5 (PB-5) are constructed using the discrete element method (DEM). The pore-scale heat transfer characteristics of hydrogen flow at low pore Reynolds numbers (Rep < 100) are investigated using a DEM-CFD simulation approach, with the temperature-dependent thermo-properties of hydrogen being considered. Distinct local channeling flow patterns are revealed by detailed analyses of the flow fields in PB-4 and PB-5. The overall friction factors for both beds are found to agree well with empirical correlations. Notably, a faster spatial temperature increase is exhibited by PB-5, with a larger D/d ratio, as evidenced by a shorter axial distance for fully-heated hydrogen flow compared to PB-4. For the pore-scale heat transfer in the packed beds, the radial temperature profiles are compared at various heights of the packed beds depending on the radial porosity oscillation, in which the wall effect should be especially considered in the near-wall region. Furthermore, the axial pore-scale Nusselt number (Nup,axial) exhibits an inverse fluctuation with the axial porosity oscillation. Finally, the global Nusselt numbers (Nu) in the packed beds are analyzed under different operating conditions, which are in good agreement with empirical correlations.

中文翻译：

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随机填充床内氢气流传热特性的数值研究


在本研究中，使用离散元构建了两个随机填充床，其管与颗粒直径 (D/d) 之比分别为 D/d = 4 (PB-4) 和 D/d = 5 (PB-5)方法（DEM）。使用 DEM-CFD 模拟方法研究了低孔隙雷诺数 (Rep < 100) 下氢气流的孔隙尺度传热特性，并考虑了氢气与温度相关的热性能。通过对 PB-4 和 PB-5 中流场的详细分析，揭示了独特的局部窜流模式。发现两个床的总体摩擦系数与经验相关性非常吻合。值得注意的是，PB-5 表现出更快的空间温度升高，具有更大的 D/d 比，这一点可以通过与 PB-4 相比全加热氢气流的轴向距离更短来证明。对于填充床中的孔隙尺度传热，根据径向孔隙率振荡，比较填充床不同高度处的径向温度分布，其中应特别考虑近壁区域的壁效应。此外，轴向孔隙尺度努塞尔数（Nup，轴向）表现出与轴向孔隙度振荡相反的波动。最后，对不同运行条件下填充床的全局努塞尔数（Nu）进行了分析，与经验相关性吻合较好。