  We present a modified TREESPH code to model galaxies in 3d. The model
includes a multi-phase description of the interstellar medium which combines
two numerical techniques. A diffuse warm/hot gas phase is modelled by SPH while
a sticky particle scheme is used to represent a cloudy medium. Interaction
processes, such as star formation and feedback, cooling and mixing by
condensation and evaporation, are taken into account. Here we apply our model
to the evolution of a Milky Way type galaxy. After an initial stage, a
quasi-equilibrium state is reached. It is characterised by a star formation
rate of ~1 M_sun/year. Condensation and evaporation rates are in balance at
0.1-1 M_sun/year.
