Accurate Two-Parameter Equation of State for Hydrogen

This study developed and validated a new simple and improved two-parameter high-quality equation of state (EOS) for hydrogen that can be used with less computational burden for the accurate description of various processes regarding underground hydrogen storage. Variation in hydrogen gas density with pressure was described by the modified power-law equation by relating density variation to deviations of density from the low-end and high-end limit values of density. The high-end limit density dependence on temperature was described by an Arrhenius-type asymptotic exponential function. The parameters of this EOS were determined by requiring thermodynamic consistency. This simple two-parameter EOS is thermodynamically consistent because the molar density is equal to zero, and its derivative with respect to pressure is equal to 1/(RT), like an ideal gas EOS when pressure approaches zero (T is absolute temperature, and R is the universal gas constant). This new simple EOS correlates hydrogen density efficiently using experimental data over 0–100 MPa and 220–473 K and molecular simulation data over the 14.03–116.064 MPa and 310.9–470 K ranges of pressures and temperatures. The new EOS is very accurate, as indicated by the coefficients of correlation being almost equal to unity (R2 = 0.9999), the relative difference between the correlation and measured density values being very close to zero (RMSE = 0.0032), and the percentage average absolute value of the relative deviation of the EOS correlation density values ρEOS from the experimental density values ρData being (ρData/ρEOS − 1)100 = 0.15% average uncertainty.