van der Waals-like transition in fluidized granular matter: hydrodynamic description

A phase separation of fluidized granular matter is presented. Molecular dynamics simulations of grain system, in two spatial dimensions, with a vibrating wall and without gravity exhibit appearance, coagulation, and evaporation of bubbles. The instability is produced by the existence of a negative compresibility region, that is caused by the energy dissipation at collisions. The phenomenon is analogous to the spinodal decomposition of the gas-liquid transition of the van der Waals model. A hydrodynamic model gives account for,the negative compresibility and predicts a critical point that is in qualitative agreement with the results of the simulations. In the onset of phase separation, we have deduced a macroscopic model that agrees quite well with molecular dynamics simulations.