  In what follows, we investigate the relation between the Friedmann and
thermodynamic pressure equations, through solving the Friedmann and
thermodynamic pressure equations simultaneously. Our investigation shows that a
perfect fluid, as a suitable solution for the Friedmann equations leading to
the standard modelling of the universe expansion history, cannot simultaneously
satisfy the thermodynamic pressure equation and those of Friedmann. Moreover,
we consider various energy definitions, such as the Komar mass, and solve the
Friedmann and thermodynamic pressure equations simultaneously to get some
models for dark energy. The cosmological consequences of obtained solutions are
also addressed. Our results indicate that some of obtained solutions may unify
the dominated fluid in both the primary inflationary and current accelerating
eras into one model. In addition, by taking into account a cosmic fluid of a
known equation of state, and combining it with the Friedmann and thermodynamic
pressure equations, we obtain the corresponding energy of these cosmic fluids
and face their limitations. Finally, we point out the cosmological features of
this cosmic fluid and also study its observational constraints.
