Density Measurements for High-Temperature Helium–Xenon Mixtures

Helium–xenon mixtures have been widely recognized as promising working fluids for high-temperature gas-cooled reactors (HTGRs) and their integrated Brayton power cycles, owing to their favorable compressibility characteristics, excellent thermal stability under extreme conditions, and environmentally benign nature. The thermophysical properties of helium–xenon mixtures can be adjusted by varying the mixing ratio, which in turn influences cycle performance, heat transfer characteristics, and operational safety. Among these properties, density plays a pivotal role in thermal–hydraulic design, as it directly governs the determination of key operating parameters, including pressure, mass flow rate, and heat transfer coefficients. In this study, the density of helium–xenon mixtures was experimentally determined using a Burnett constant-volume apparatus. Measurements were conducted over a temperature range of 313–773 K and at pressures up to 6 MPa. The experimental data were correlated using a virial equation of state, yielding average absolute percentage deviations within 2.5%. Furthermore, the present results were systematically compared with available literature data, demonstrating satisfactory consistency and reliability.