The Joule-Thomson effect is also known as the Joule-Kelvin effect. This effect is present in non ideal gasses, where a change in temperature occurs upon expansion. Introduction The Joule-Thomson coefficient is given by \[\mu_{\mathrm JT} = \left. \dfrac{\partial T}{\partial p} \right\vert_H\] where T is the temperature, p is the pressure and H is the enthalpy. In terms of heat capacities one has \[\mu_{\mathrm JT} C_V = -\left. \dfrac{\partial E}{\partial V} \right \vert_T \] and \[\mu_{\mathrm JT} C_p = -\left. \dfrac{\partial H}{\partial p} \right \vert_T \] In terms of the second virial coefficient at zero pressure one has \[\mu_{\mathrm JT}\vert_{p=0} = ^0\!\!\phi = B_2(T) -T \dfrac{dB_2(T)}{dT}\] References Jacques-Olivier Goussard and Bernard Roulet "Free expansion for real gases", American Journal of Physics 61 pp. 845-848 (1993) E. Albarran-Zavala, B. A. Espinoza-Elizarraraz, F. Angulo-Br ﻿ own "Joule Inversion Temperatures for Some Simple Real Gases", The Open Thermodynamics Journal 3 pp. 17-22 (2009) Thomas R. Rybolt "A virial treatment of the Joule and Joule-Thomson coefficients", Journal of Chemical Education 58 pp. 620-624 (1981)