Phase separation of a driven granular gas in annular geometry

Area of Science:

• Soft Matter Physics
• Granular Materials
• Statistical Mechanics

Background:

• Investigates phase separation in a granular gas of hard disks within a 2D annulus.
• The inner boundary acts as a thermal wall, influencing particle behavior.

Purpose of the Study:

• To analyze the spontaneous symmetry breaking and phase separation in this confined granular system.
• To compare theoretical predictions from granular hydrodynamics with molecular dynamics simulations.

Main Methods:

• Utilized granular hydrodynamic equations to model the system's behavior.
• Performed event-driven molecular dynamics (MD) simulations to validate theoretical findings.
• Analyzed the azimuthal spectrum of particle density to identify phase transitions.

Main Results:

• Hydrodynamics predicts a stable, azimuthally symmetric state with higher density at the annulus exterior.
• Sufficiently large inelastic energy loss leads to spontaneous symmetry breaking and phase separation.
• Simulations confirm the predicted instability region and identify a broader phase separation region, including metastable states.

Conclusions:

• The study demonstrates a van der Waals-like phase separation in a 2D annular granular gas.
• The instability is influenced by heat conduction, which tends to suppress it.
• Phase separation is robust, persisting under variations of wall properties and driving mechanisms.