Engineering Approximation of Saturated-Vapor P-v-T Behavior Using a Gas-Specific Temperature-Dependent Fitting Parameter: A Gas-Specific Empirical Correlation

Accurate prediction of thermodynamic properties of real gases is essential for the analysis and design of energy systems such as power plants, gas turbines, and energy conversion processes. Although many equations of state have been developed, they still have limitations in accurately predicting the behavior of real gases, especially near the critical point. Unlike previous studies that focused on refining parameters embedded in conventional equations of state, this study introduces a gas-specific, data-driven approach by adjusting the specific gas constant in the ideal gas law. The gas-specific fitting parameter Rcorr is evaluated directly from experimentally measured saturated-vapor P-v-T data and has the same units as the specific gas constant; however, it does not represent a modified or redefined physical gas constant. The proposed method should be interpreted as an empirical engineering correlation rather than as a predictive thermodynamic equation of state. Despite its simple formulation, the ideal gas law incorporating the corrected specific gas constant showed agreement with experimental data comparable to that of the Peng–Robinson–Stryjek–Vera equation of state over most of the saturation range, except near the critical point. For saturated steam, the proposed correlation reduced the pressure deviation to within approximately ±2.6% over most of the saturated-vapor region. Although the present assessment is limited to the dataset used to develop the correlation, the proposed correlation provides engineering-level accuracy while retaining a compact analytical form, making it suitable for repeated saturated-vapor P-v-T evaluations.