Lattice Boltzmann simulations of capillary filling: finite vapour   density effects
  Numerical simulations of two-dimensional capillary filling using the pseudo-potential lattice Boltzmann model for multiphase fluids are presented, with special emphasis on the role of finite-vapour density effects. It is shown that whenever the density of the light-phase exceeds about ten percent of the dense phase, the front motion proceeds through a combined effect of capillary advection and condensation. As a result, under these conditions, the front proceeds at a higher speed as compared to the Washburn prediction. It is suggested that such an acceleration effect might be observed in experiments performed sufficiently close to critical conditions 
F. Diotallevi, L.Biferale, S. Chibbaro, G. Pontrelli, F. Toschi, and   S. Succi