  The mixed morphology class of supernova remnants (MMSNRs) comprises a
substantial fraction of observed remnants and yet there is as yet no consensus
on their origin. A clue to their nature is the presence of regions that show
X-ray evidence of recombining plasmas. Recent calculations of remnant evolution
in a cloudy interstellar medium (ISM) that included thermal conduction but not
non-equilibrium ionization (NEI) showed promise in explaining observed surface
brightness distributions but could not determine if recombining plasmas were
present. In this paper, we present numerical hydrodynamical models of MMSNRs in
2D and 3D including explicit calculation of NEI effects. Both the spatial
ionization distribution and temperature-density diagrams show that
recombination occurs inside the simulated MMSNR, and that both adiabatic
expansion and thermal conduction cause recombination, albeit in different
regions. Features created by the adiabatic expansion stand out in the spatial
and temperature-density diagrams, but thermal conduction also plays a role.
Thus thermal conduction and adiabatic expansion both contribute significantly
to the cooling of high-temperature gas. Realistic observational data are
simulated with both spatial and spectral input from various regions. We also
discuss the possibility of analyzing the sources of recombination and dominant
hydrodynamical processes in observations using temperature-density diagrams and
spatial maps.
