Henderson hard disk equation of state

Henderson hard disk equation of state (Eq. 5 ):

$Z=\frac{pV}{N{k}_{B}T}=\frac{1+y^2/8}{(1-y{)}^2}.$

where:

• $Z$ is the compressibility factor
• $p$ is the pressure
• $V$ is the volume
• $N$ is the number of particles
• $k_B$ is the Boltzmann constant
• $T$ is the absolute temperature
• $y=(\pi /2)\rho {\sigma }^2$