  We study the finite size effects on the thermal deconfinement phase
transition from the hadronic gas phase to the QGP phase, using a simple
thermodynamic model based on the coexistence of confined and deconfined phases
in a finite volume. We first consider the bag model partition function for the
QGP, then we include the necessary color singletness condition. By probing the
behavior of some physical quantities on the hole range of temperature, it turns
out that in a finite size system, all singularities occuring in these
quantities in the thermodynamic limit are smoothed out, and the phase
transition is then rounded over a broadened critical region, with an additional
shifting effect of the critical point induced by the exact color singletness
requirement. An analysis of the finite size scaling behavior at criticality of
some characteristic quantities allows us to determine the scaling critical
exponents characterizing the thermal deconfinement phase transition. The
obtained results are in good agreement with those predicted by other studies
for a first-order phase transition
