  We compare the lattice results on QCD phase diagram for two and three flavors
with the hadron resonance gas model (HRGM) calculations. Lines of constant
energy density $\epsilon$ have been determined at different baryo-chemical
potentials $\mu_B$. For the strangeness chemical potentials $\mu_S$, we use two
models. In one model, we explicitly set $\mu_S=0$ for all temperatures and
baryo-chemical potentials. This assignment is used in lattice calculations. In
the other model, $\mu_S$ is calculated in dependence on $T$ and $\mu_B$
according to the condition of vanishing strangeness. We also derive an
analytical expression for the dependence of $T_c$ on $\mu_B/T$ by applying
Taylor expansion of $\epsilon$. In both cases, we compare HRGM results on
$T_c-\mu_B$ diagram with the lattice calculations. The agreement is excellent,
especially when the trigonometric function of $\epsilon$ is truncated up to the
same order as done in lattice simulations. For studying the efficiency of the
truncated Taylor expansion, we calculate the radius of convergence. For zero-
and second-order radii, the agreement with lattice is convincing. Furthermore,
we make predictions for QCD phase diagram for non-truncated expressions and
physical masses. These predictions are to be confirmed by heavy-ion experiments
and future lattice calculations with very small lattice spacing and physical
quark masses.
