Progress toward new Reference Correlations for the Transport Properties of Carbon Dioxide | NIST

While the thermodynamic properties of CO2 are available with excellent accuracy from the referencequality equation of state of Span and Wagner, the current reference correlations for transport properties (thermal conductivity and viscosity) are relatively old and have significant room for improvement. We describe current work at NIST to improve the data situation for both transport properties. For the viscosity, new theoretical results for the dilute vapor and a semitheoretical scaling approach for the liquid allow us to produce an improved correlation. In the case of the thermal conductivity, we measured new data with a transient hot-wire instrument. These measurements cover temperatures from 219 K to 751 K at pressures up to 69 MPa, with uncertainties near 0.5 % for the liquid and compressed gas, increasing to 3 % for low-pressure gases and conditions very near the critical point. This improves the uncertainty at most conditions by more than a factor of two compared to previous measurements. These new data, in combination with literature data and theoretical results for the dilute gas, are being employed to produce a new standard correlation for the thermal conductivity as a function of temperature and density. The new correlation will employ state-of-the-art theory to incorporate the near-critical enhancement of the thermal conductivity that is significant in a sizable region around the critical point.