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Microscopic model for a granular solid-liquid-like phase transition

julio 18 / 11:00 am - 12:00 pm

Dr. Nicolás Mujica

Departamento de Física
FCFM, Universidad de Chile
Forced granular matter in confined geometries present phase transitions and coexistence. Depending on system and forcing parameters, both liquid-vapor and liquid-solid coexisting states are possible. From a macroscopic point of view, phase separation occurs because the system becomes mechanically unstable, presenting an effective negative compressibility for certain parameters. Indeed, the equation of state has shown to be similar to the van der Waals law for molecular fluids. For the solid-liquid coexistence that is observed in quasi-two-dimensional vibrated systems, both first and second order transitions have been reported. Here, we present a model that explains the microscopic origin of this granular phase transition and coexistence. We consider the energy input and dissipation balance of non-cohesive, dissipative spheres confined in vibrated shallow box. Experiments show that particles in the solid cluster move collectively, synchronized with the cell’s vibration, in a similar way as the collect-and-collide regime that is observed in granular dampers. Imposing this condition, modeling the solid cluster as an effective particle of zero restitution coefficient, and mechanical equilibrium between the two phases, using a state equation that has been validated for hard disks, we obtain a power balance equation that relates the characteristic vertical and horizontal velocities to the microscopic relevant parameters (geometric and dissipation coefficients) as well as to the vibration amplitude and solid cluster’s size. Predictions of our model are compared with experimental results, as well as with experimental and dynamic simulation results from other groups, finding a good agreement.

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Detalles

Fecha:
julio 18
Hora:
11:00 am - 12:00 pm

Lugar

Sala Seminarios 3er piso, DFI
Av Blanco Encalada 2008
Santiago, Chile
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