High-Speed Particles Rebound with Unexpected Energy on Liquid-Coated Surfaces

Key Findings

Researchers have discovered that high-speed particles impacting liquid-coated surfaces rebound with greater energy than previously expected. The study, published in the International Journal of Multiphase Flow, combined experiments and numerical simulations to explain the mechanism.

• At increasing impact speeds, the liquid film between the particle and the wall changes from a "bridge" to a "dome" shape.
• This transition is driven by cavitation: the pressure in the gap drops below saturated vapor pressure, forming a vapor cavity.
• The vapor cavity weakens the attractive force of the liquid on the rebounding particle, reducing energy loss and resulting in a higher coefficient of restitution (COR).

"At increasing impact speeds, the liquid film between the particle and the wall changes from a 'bridge' to a 'dome' shape."

Background

The coefficient of restitution (COR) measures the fraction of kinetic energy retained after a collision. Understanding COR is critical for industries such as:

• Pharmaceuticals
• Food coating
• Heavy machinery

In these sectors, particle impacts occur regularly. The push for carbon neutrality has led to faster motors in aviation and automotive sectors, increasing the risk of damage from high-speed debris. Liquid films are used as a cushion, but their behavior at high speeds—tens of meters per second—was not well understood until now.

Statement

"Although particle collisions on wet walls have been extensively studied, this research focused on high-speed collisions and identified phenomena that differ from those reported in previous literature."

— Hironori Hashimoto, lead author of the study

Hashimoto added that the dynamics are complex and that further research will aim to improve industrial equipment performance and safety.