Experimental Study of the Joule-Thomson Effect in Carbon Dioxide

Joule-Thomson effect in carbon dioxide.—(1) Experimental results for both vapor and liquid phases for 20 to 75 atm. and 0 to 120°C. Dried C${\mathrm{O}}_2$, after compression to a high pressure controlled by a special regulator, was brought to a definite temperature, then adiabatically expanded radially inward through the walls of a porous porcelain tubular plug, successively to each of several lower pressures controlled by a second regulator. Pressures were measured with a modified Amagat differential free-piston manometer; the temperatures before and after passage through the plug were measured by Pt resistance thermometers. Since the expansion was adiabatic, the enthalpy, $g=(u+pv)\mathrm{}$, was constant, and the observations secured, properly reduced, yielded isenthalpic throttling curves the slopes of which determine $\mu ={\left(\frac{\partial t}{\partial p}\right)}_g$, the Joule-Thomson coefficient. For both liquid and vapor phases $\mu$ is found to be a linear function of the isenthalpic temperatures and an exponential function of the isenthalpic pressures of such curves. In the liquid region $\mu$ becomes zero at -24°C for all pressures involved, and is negative at lower temperatures. The C${\mathrm{O}}_2$ used contained from 0.25 to 1.5 per cent air, but the author's results, obtained in 1910, are consistent with those of Jenkin and Pye (1914, 1915) which extended down to 10 atm. and to -55°C and were obtained with purer C${\mathrm{O}}_2$; also with those of Kester, and of Joule and Thomson, where comparable. (2) Empirical formulas. The entire experimental field for both phases, including the transition region in the vicinity of the critical point and along the saturation curve, has been represented by an empirical formulation, necessarily rather complicated. Isenthalps, isotherms and isobars of $t$, $p$, and $\mu$ computed from these formulas for the range 0 to 100 atm. from the solid-liquid phase-boundary at about -55°C through the liquid field into the super-heated vapor field as far as +150°C are presented in tabular and graphical form. More complete details will be given in a Bulletin of the University of Wisconsin.