Yue Shuang¹， Yu Wei¹， Zhang Ning²， Yuan Fangyang¹

1.School of Mechanical Engineering， Jiangnan University， Wuxi 214122， China； 2.Shanghai Institute of Applied Physics， Chinese Academy of Sciences， Shanghai 201800， China

Abstract

Objective This study investigates how the geometry of disturbance columns affects the contact-based agglomeration tendency of dry micron-sized particles in the off-gas treatment system of a molten salt reactor. Rather than relying solely on macroscopic quantities such as outlet concentration or mean particle size， particle-scale contact relationships extracted from discrete element method outputs are analyzed. The objectives are to quantify contact pairs （CP）， contact clusters （CC）， persistent contact pairs （PCP）， size-resolved contact participation， and the pressure-drop cost of contact enhancement， and to identify a cross-shaped column for subsequent low-resistance optimization. These contact-based indicators characterize particle contact opportunities and contact network development rather than irreversible physical agglomeration.

Methods A two-way coupled computational fluid dynamics-discrete element method （CFD-DEM） model was established using ANSYS Fluent and Rocky DEM to compare the performance of a circular cylinder， a wavy column， and a cross-shaped column under identical operating conditions. The computational domain was 25 mm × 15 mm×2 mm， the inlet velocity was 1.5 m/s， and the column center was located 5 mm downstream of the inlet. Particles with diameters of 2， 5， 10， and 20 μm and a density of 2 000 kg/m³ were injected at 2×10⁶ particles/s for each size. The gas-phase flow was resolved using the SST k-ω-based stress-blended eddy simulation （SBES） model， with the wall-adapting local eddy-viscosity （WALE） model applied in the scale-resolving region. Pressure-velocity coupling was performed using the PISO algorithm， and dry adhesive contacts were described by the Johnson-Kendall-Roberts （JKR） model with a particle-particle surface energy of 1 J/m². Mesh independence was assessed using three mesh densities for each geometry， and the medium-density meshes were selected to balance wake resolution and computational cost. The total simulation time was 0.10 s， with statistics calculated over 0.04-0.10 s after the initial filling stage. A CP was defined as a pair of particles in direct contact within an output frame； a CC was defined as a connected particle-contact network； and a PCP was defined as a unique particle pair that remained continuously in contact for at least 2， 3， or 5 consecutive frames. Additional indicators included particle-size-specific contact participation rates， particle-size-combination contributions， pressure-normalized contact-pair and contact-cluster indices， and a power-normalized contact-pair index. Five cross-shaped candidates， Cross-0—Cross-4， were further evaluated using the CRITIC-TOPSIS method.

Results and Discussion The three disturbance columns produced distinct wake structures and particle-contact responses. The circular cylinder generated a conventional bluff-body wake with a localized velocity deficit and alternating shear layers， whereas the wavy column extended the disturbed region downstream but provided limited transverse entrainment. The cross-shaped column introduced multiple separation points and interacting shear layers， creating a wider and more heterogeneous wake that increased particle migration， local residence time， and trajectory overlap. During the stable statistical window， the average numbers of contact pairs were 4 187.6， 3 937.4， and 7 849.2 for the circular cylinder， wavy column， and cross-shaped column， respectively. Therefore， the cross-shaped column increased the average CP number by 87.4% and 99.4% relative to the other two structures. It also promoted the formation of multi-particle contact networks， producing 460.6 three-particle clusters and 295.2 clusters with at least four particles per frame. Its average maximum cluster size was 23.2 particles， with an instantaneous maximum of 33 particles. Although most contacts were short-lived， the cross-shaped column maintained substantially more long-duration contacts. Under the criterion of at least five consecutive frames， 2 747 unique PCPs were identified， compared with 13 for the circular cylinder and 10 for the wavy column.Contact participation increased with particle diameter. For the cross-shaped column， the participation rates of 2， 5， 10， and 20 μm particles were 2.82%， 3.72%， 6.64%， and 19.04%， respectively. Different-size contacts dominated for all geometries， while the cross-shaped column increased the contribution of same-size contacts to 32.40%. The 10 μm-20 μm and 20 μm-20 μm pairs showed the strongest enhancement， reaching （2 488.6±175.3） and （2 161.0±191.2） CPs， respectively. This enhancement resulted in a higher hydraulic penalty， with pressure drops of 0.498， 1.970， and 2.437 Pa for the circular cylinder， wavy column， and cross-shaped column， respectively. Consequently， the circular cylinder achieved the highest contact-pair number per unit pressure drop， whereas the cross-shaped column provided the greatest absolute enhancement in CPs and CCs. These normalized indicators represent contact opportunities relative to flow resistance rather than the net particle-collection efficiency. Among the five cross-shaped candidates，Cross-2， with a longer streamwise arm，achieved the highest CRITIC-TOPSIS score of 1.000 and the best overall performance in pressure-normalized contact-pair enhancement，maximum cluster size，persistent contacts，and contacts involving 20 μm particles.

Conclusion The cross-shaped column most effectively strengthens the contact-based agglomeration tendency of dry micron-sized particles by widening the wake，increasing particle trajectory overlap，and sustaining larger contact networks.Its advantage is especially evident for contacts involving 20 μm particles and persistent contacts， but it is accompanied by a higher pressure drop. The circular cylinder is more economical when contact enhancement is evaluated per unit pressure drop. Under the present operating conditions and evaluation framework， Cross-2 provides the best overall balance among the screened cross-shaped columns and is recommended as the reference configuration for further low-resistance optimization while maintaining multiple shear layers and a broad wake.

Keywords： micron-sized particle； disturbance column； contact-based agglomeration； computational fluid dynamics-discrete element method； contact cluster

Get Citation:  Yue Shuang， Yu Wei， Zhang Ning， et al. Influence of disturbance columns on particle agglomeration in off-gas treatment system of a molten-salt reactor［J］. China Powder Science and Technology， 2027， 33（2）： 1-13.

Received :  2026-07-01， Revised： 2026-08-27，Online： 2026-09-29。

Funding： This research was supported by the National Natural Science Foundation of China (Grant No. 12172152).

DOI：10.13732/j.issn.1008-5548.2027.02.004

CLC No.:  O359； TB4

Type Code:  A

Serial No.:  1008-5548（2027）02-0001-13