Molecular dynamics study on coalescence interface evolution of collided dry ice particles

L Teng and W Lin and X Huang and ZC Li and HR Li and PB Yin and SH Rao, PROCESS SAFETY AND ENVIRONMENTAL PROTECTION, 202, 107709 (2025).

DOI: 10.1016/j.psep.2025.107709

CO2 pipeline leaks associated with intense throttling effects generate flows of dry ice particles that tend to coalesce and deposit on pipe walls, leading to blockages. Adopting molecular dynamics simulations, the collisions of nanoscale dry ice particles were studied to reveal the coalescence mechanism at the molecular level. Through systematic analysis of morphological evolution during dry ice particle collisions at varying velocities, two coalescence mechanisms were identified: intermolecular force-induced adhesion under low-velocity condition (vp=100 m/s) and interfacial melting-recrystallization-driven coalescence at mid-velocities (200 m/ s <= vp <= 600 m/s). High-velocity collisions (vp >= 700 m/s) were observed to trigger complete particle melting, accompanied by significant molecular dissipation, which suppressed recrystallization and led to the formation of unstable disordered aggregates. Quantitative investigation reveals that under low-to-mid velocity conditions, the coalescence degree dominated by phase transitions strengthens with increasing velocity. At lower velocities, larger particles exhibit weaker coalescence due to stronger interfacial molecular confinement by potential fields, while at higher velocities, increased particle size amplifies momentum transfer, thereby enhancing coalescence. This study elucidated the collision-coalescence mechanisms of dry ice particles at the molecular level, providing a theoretical foundation for enhancing the safety of CO2 pipeline engineering.

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