  Heavy ion collisions have been widely used in the last decade to constraint
the parameterizations of the symmetry energy term of nuclear equation of state
(EOS) for asymmetric nuclear matter as a function of baryonic density. In the
Fermi energy domain one is faced with variations of the density within a narrow
range of values around the saturation density $\rho_0$=0.16 fm$^{-3}$ down
towards sub-saturation densities. The experimental observables which are
sensitive to the symmetry energy are constructed starting from the detected
light particles, clusters and heavy fragments that, in heavy ion collisions,
are generally produced by different emission mechanisms at different stages and
time scales of the reaction. In this review the effects of dynamics and
thermodynamics on the symmetry energy in nuclear reactions are discussed and
characterized using an overview of the data taken so far with the CHIMERA
multi-detector array.
