Joule-Thomson coefficient ($\mu =(\partial T/\partial p{)}_H$)

The temperature change per pressure change at fixed enthalpy is $\mu =(\partial T/\partial p{)}_H=[T(\partial V/\partial T{)}_p-V]/C_p$. A positive coefficient means cooling under an adiabatic throttle pressure drop.

For $p=k_{B}T[n+B_2(T)n^2]$, the coefficient is $\mu =N[T{B}_2^{\prime }-B_2]/[C_p(1+2B_{2}n)]$. On the stable dilute branch it is positive precisely when $d(B_2/T)/dT>0$.