Summary: Internal Energy Relaxation Models in
For a gas in thermal equilibrium, individual
molecules are constantly gaining and losing
energy through collisions, but the total change in
energy is zero.
Establishment of equilibrium takes some time.
We've looked at the DSMC modeling of
approach to equilibrium for a system of hard
sphere molecules initially all having the same
speed. The time it took the distribution function
to approach Maxwellian was several mean
Diatomic and polyatomic molecules possess internal
energy and this energy can also be exchanged in
collision in addition to translational energy.
In equilibrium, the total thermal energy is equipartioned:
each energy mode of a molecule on average has
energy proportional to the number of degrees of
freedom times temperature: