  Thermodynamic and transport properties of nuclear fireball created in the
central region of heavy-ion collisions below 400 MeV/nucleon are investigated
within the isospin-dependent quantum molecular dynamic (IQMD) model. These
properties including the density, temperature, chemical potential, entropy
density ($s$) and shear viscosity ($\eta$), are calculated by a generalized hot
Thomas Fermi formulism and a parameterized function, which was developed by
Danielewicz. As the collision goes on, a transient minimal
$\eta/s=5/4\pi-10/4\pi$ occurs in the largest compression stage. Besides, the
relationship of $\eta/s$ to temperature ($T$) in the freeze-out stage displays
a local minimum which is about 9-20 times $1/4\pi$ around $T$ = 8-12 MeV, which
can be argued as indicative of a liquid gas phase transition. In addition, the
influences of nucleon-nucleon (NN) cross section ($\sigma_{NN}$) and symmetry
energy coefficient ($C_{s}$) are also discussed, and it is found that the
results are sensitive to $\sigma_{NN}$ but not to $C_{s}$.
