  Generalized mean-field approach for thermodynamic description of relativistic
single- and multi-component gas in the grand canonical ensemble is formulated.
In the framework of the proposed approach different phenomenological
excluded-volume procedures are presented and compared to the existing ones. The
mean-field approach is then used to effectively include hard-core repulsion in
hadron-resonance gas model for description of chemical freeze-out in heavy-ion
collisions. We calculate the collision energy dependence of several quantities
for different values of hard-core hadron radius and for different
excluded-volume procedures such as van der Waals and Carnahan-Starling models.
It is shown that a choice of the excluded-volume model becomes important for
large particle densities. For large enough values of hadron radii
($r\gtrsim0.9$ fm) there can be a sizable difference between different
excluded-volume procedures used to describe the chemical freeze-out in
heavy-ion collisions. At the same time, for the smaller and more commonly used
values of hard-core hadron radii ($r\lesssim0.5$ fm), the precision of the van
der Waals excluded-volume procedure is shown to be sufficient.
