Calorimetry in the near-critical and supercritical regions. Nitrous oxide + hydrocarbon mixtures
The high pressure calorimeters developed in the last 20 years are briefly reviewed. Most of them have been used to obtain excess enthalpy data (H E) in the critical and supercritical regions. Data are available for many mixtures formed by carbon dioxide and for a few involving other supercritical fluids such as ethane, methane, nitrous oxide, etc. Data for several N2O ˛ hydrocarbon mixtures were recently measured from 308.15 to 323.15 K and from 7.64 to 15.00 MPa. Excess enthalpies for N2O ˛ hydrocarbon mixtures were calculated using several cubic equations of state (EOS). Two noncubic EOS which combine the Carnahan-Starling hard-sphere term with the van der Waals and Redlich-Kwong attractive terms, were also used. The classical van der Waals mixing rules and those proposed by Wong and Sandler were used. The ability of the cubic EOS to correlate the excess enthalpies of the N2O ˛ hydrocarbon mixtures seems to be related to the proximity of conditions of temperature and pressure to the N2O critical point.