Effects of cylindrical particle structure modification on the flow and heat transfer characteristics in packed beds

doi:10.11949/0438-1157.20241343

Abstract

Abstract:

To investigate the effects of different modified cylindrical particle shapes on the wall effect and flow-heat transfer characteristics in packed beds, computational fluid dynamics (CFD) methods were employed to perform numerical simulations on six types of packed beds filled with particles: unmodified cylindrical particles and modified single-hole cylindrical, 3-hole cylindrical, trilobe, 3-hole trilobe, and 9-hole trilobe particles. The radial and axial porosity distributions, flow characteristics, and flow-heat transfer performance were analyzed. The results show that the cylindrical particles can improve the uniformity of fluid flow by either internal openings or external slots. Internal perforation reduces the proportion of flow near the wall, and the number of perforations has no significant effect on the flow near the wall. However, increasing the number of perforations weakens the uniformity of radial flow distribution while enhancing the uniformity of axial flow distribution. External grooving of cylindrical particles into a Trilobe shape improves the heat transfer coefficient but significantly increases the unit pressure drop. In contrast, internal perforation reduces both the heat transfer coefficient and unit pressure drop. Increasing the number of perforations enhances heat transfer performance but also results in a higher pressure drop. Considering both heat transfer performance and flow resistance, the mixed-modified 9-hole trilobe particles exhibit the highest overall heat transfer efficiency and demonstrate the best comprehensive heat transfer performance.

Key words: packed bed, numerical simulation, flow, heat transfer, cylindrical particle

摘要：

为研究不同修饰形状的圆柱颗粒对填充床壁面效应及流动换热特性的影响，采用计算流体力学（CFD）方法，对未修饰的圆柱颗粒及修饰后的单孔圆柱、3孔圆柱、三叶草、3孔三叶草和9孔三叶草6种颗粒填充床进行了数值模拟。分析了径向与轴向空隙率分布、流动特性及流动换热性能。结果表明，圆柱颗粒通过内部开孔或外部开槽修饰均能够改善流体流动均匀性；颗粒内部开孔可以减小壁面附近流量占比，且孔洞数量对近壁面流量的影响不显著，但增加孔洞数量会削弱流体径向流动均匀性，同时提升轴向流动均匀性；圆柱颗粒通过外部开槽为三叶草状后可提升传热系数，但显著增加单位压降，通过内部开孔后传热系数和单位压降均降低；增加孔洞数量能够提升换热性能，但同时会导致压降增加；综合考虑传热效果和流动阻力，混合修饰的9孔三叶草颗粒具备最高的总换热效率，表现出最佳的综合换热性能。

关键词: 填充床, 数值模拟, 流动, 换热, 圆柱颗粒

CLC Number:

TQ 021.1

Xing BAO, Xueyan GUO. Effects of cylindrical particle structure modification on the flow and heat transfer characteristics in packed beds[J]. CIESC Journal, 2025, 76(6): 2603-2615.

包兴, 郭雪岩. 圆柱颗粒结构修饰对填充床内流动和换热特性的影响[J]. 化工学报, 2025, 76(6): 2603-2615.

Figures/Tables 17

Fig.1 Physical model of packed beds with different particle shapes

Table 1 Geometrical parameters of randomly packed bed

颗粒形状	颗粒体积 $V p$ /mm³	孔洞体积 $V h o l e$ /mm³	孔洞比表面积 $S T V h o l e$ /m^-1	颗粒个数 $N$	堆积高度 $L$ /mm
圆柱	21.2	—	—	173	40.5
单孔圆柱	14.4	6.8	2352	173	40.8
3孔圆柱	14.4	6.8	4068	173	40.7
三叶草	14.3	—	—	243	40.6
3孔三叶草	7.5	6.8	4068	244	40.1
9孔三叶草	7.5	6.8	7049	244	40.1

Table 1 Geometrical parameters of randomly packed bed

颗粒形状	颗粒体积 $V p$ /mm³	孔洞体积 $V h o l e$ /mm³	孔洞比表面积 $S T V h o l e$ /m^-1	颗粒个数 $N$	堆积高度 $L$ /mm
圆柱	21.2	—	—	173	40.5
单孔圆柱	14.4	6.8	2352	173	40.8
3孔圆柱	14.4	6.8	4068	173	40.7
三叶草	14.3	—	—	243	40.6
3孔三叶草	7.5	6.8	4068	244	40.1
9孔三叶草	7.5	6.8	7049	244	40.1

Table 2 Property parameter

物质

密度/(kg·m^-3)

比热容/

(J·kg^-1·K^-1)

动力黏度/

(kg·m^-1·s^-1)

Table 3 Control parameters for grid generation

参数	数值
基准尺寸/mm	2.50、2.75、3.00
面网格尺寸/mm	基准尺寸×8%
增长率	1.2
边界层数	2
边界层厚度/mm	基准尺寸×2%

Fig.2 Grid independence verification

Fig.3 Longitudinal section view of the mesh

Fig.4 Validation of particle packing model

Fig.5 Comparison of axial pressure drop in cylindrical particle packed bed of CFD simulation results and correlation-based calculations

Fig.6 Radial distribution of porosity and average velocity in packed beds with different particle shapes

Fig.7 Axial distribution of porosity and average velocity in packed beds with different particle shapes

Fig.8 Mass flow rate distribution in cross-sectional annular regions

Fig.9 Velocity distribution on Z-direction profile of packed beds with different particle shapes

Fig.10 Variation of unit pressure drop with inlet velocity in packed beds with different particle shapes

Fig.11 Variation of turbulence dissipation rate with inlet velocity in packed beds with different particle shapes

Fig.12 Variation of heat transfer coefficient with inlet velocity in packed beds with different particle shapes

Fig.13 Temperature distribution on Z-direction profile of packed beds with different particle shapes

Fig.14 Variation of overall heat transfer efficiency with inlet velocity in packed beds with different particle shapes

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