Dew points for hydrogen-rich (hydrogen + propane) and (hydrogen + n-butane) mixtures determined with a microwave re-entrant cavity resonator

• Dew points of hydrogen-rich binary mixtures were measured with low uncertainty. • Hydrogen can affect pressure measurement devices, thus increasing uncertainty. • Detailed comparisons with the GERG-2008 equation of state are presented. • New experimental results significantly improve the current data situation. • Data will help improve thermodynamic calculations for decarbonizing gas grids. Dew-point measurements were performed for hydrogen-rich binary mixtures with hydrocarbon mole fractions of 0.09995 C 3 H 8 , 0.1499 C 3 H 8 , 0.0513 n -C 4 H 10, and 0.09888 n -C 4 H 10 using a modified microwave re-entrant cavity apparatus. Isochoric measurements were conducted in the temperature range of (256 to 286) K with pressures up to 6.8 MPa and 2.0 MPa for mixtures containing propane and n -butane, respectively. The combined expanded uncertainties ( k = 2) in dew-point temperature and pressure were estimated to be between (0.35 and 2.0) K and (0.0011 and 0.030) MPa. The agreement with predictions of the GERG-2008 equation of state is within 5.5%. However, better agreement with predicted values was achieved using a cubic equation recently developed in-house. Moreover, experiments with short- and long-term exposure of pressure sensors to hydrogen have shown that pressure measurement, and thus the uncertainty, can be affected; further investigation on this matter is therefore inevitable to improve hydrogen thermophysical property data.