Simultaneous Composition and Density Measurements of Two-Phase Methane + Propane Mixtures with a Composite Microwave Cavity

Abstract Vapour–liquid equilibrium measurements are essential for developing equations of state, tuning binary interaction parameters, and improving the thermodynamic description of fluid mixtures. Conventionally, multiple apparatus are needed to quantify equilibrium phase behaviour and fluid properties, including composition, density, and phase fractions (quality). Using several different instruments to acquire the desired data can be laborious and increase measurement uncertainty. Microwave cavities are a promising technology capable of measuring these properties simultaneously in binary mixtures. Here, we apply recent advances in cavity design and signal processing to demonstrate measurements of phase volume fractions, compositions, and densities in mixtures of methane and propane at vapour–liquid equilibrium. Furthermore, we present an uncertainty analysis for phase composition and density measurements made with a single apparatus consisting of several microwave cavities and demonstrate levels of accuracy comparable to those obtained with conventional analytical techniques.