The small dynamical mass of dwarf spheroidals means that the
interstellar medium (ISM) binding energy is small compared to the
energy released by several supernovae, which leads the high
metallicity spread and relatively high metallicity derived for these
galaxies puzzling. I present preliminary results of 3-D hydro
simulations of the ISM evolution in dwarf spheroidal galaxies
undergoing star formation for the first time. The star formation is
assumed to occur in a sequence of instantaneus bursts separated by
quiescent periods. Different models are made changing the number and
the intensity of the bursts in such a way that the final mass of the
formed stars remains the same. We follow the enrichment of the ISM
taking into account the contribution of both type Ia and II
supernovae. The aim of our models is to find a star formation history
compatible with the observed spread of stellar age and metallicity in
such galaxies and to reproduce the observed mass-metallicity relation.
In general we are able to reproduce the metallicity distribution
function (MDF) of the stars, i.e. the mass fraction of the stars as a
function of [Fe/H] and the [O/Fe] vs. [Fe/H] plot. This last plot is
very useful because can discriminate the different contribution of
SNII and SNIa.