  Particle methods are less computationally efficient than grid based numerical
solution of the Navier Stokes equation. However, they have important advantages
including rigorous mass conservation, momentum conservation and isotropy. In
addition, there is no need for explicit interface tracking/capturing and code
development effort is relatively low. We describe applications of three
particle methods: molecular dynamics, dissipative particle dynamics and
smoothed particle hydrodynamics. The mesoscale (between the molecular and
continuum scales) dissipative particle dynamics method can be used to simulate
systems that are too large to simulate using molecular dynamics but small
enough for thermal fluctuations to play an important role.
