Henderson hard disk equation of state

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

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

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
• $y=(\pi /4)\rho \sigma ^{2}$