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 densi
ty 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
