Thomas Kraska

Systematic investigation of the phase behavior in binary fluid mixtures. II. Calculations based on the Carnahan–Starling–Redlich–Kwong equation of state

Phase diagrams of binary fluid mixtures have been calculated from the Carnahan–Starling–Redlich–Kwong equation of state in connection with standard quadratic mixing rules. The phase diagrams were classified according to the system of van Konynenburg and Scott and then used to construct global phase diagrams showing the extent of the various phase diagram classes in the space of the parameters of the equation of state. For molecules of equal size, the global phase diagram is rather similar to that of the Redlich–Kwong or the van der Waals equation. For molecules of different sizes, however, a new tricritical line appears. Such a behavior is observed for cubic equations of state only if nonadditive covolumes are assumed. Along this new tricritical line, some unusual phase diagrams involving four‐phase states and high‐density instabilities can be found. The influence of molecular size ratios on the global phase diagrams and the relationship of the equation of state of this work to the ternary symmetric lattice gas and the van der Waals lattice gas are discussed.

An equation of state for pure fluids describing the critical region

Density fluctuations of a pure nuid are treated by a cell model, in which the fluid is divided into cells containing different numbers of particles. A probability function for the particle number is derived. This function, after convolution with a classical (mean field) equation of state, leads to an improved equation of state which is valid in the critical region. The equation of state is analytical, hence not exact in the immediate vicinity of the critical point. As an example, the convolution is applied to the Carnahan-Starling/van der Waals equation of state; the resulting equation of state is used to correlate thermodynamic properties of several simple fluids.

Anomalous fluid properties of carbon dioxide in the supercritical region – Application to geological CO 2 storage and related hazards

For supercritical fluids there is a wedge-shaped region called Widom region, where several physico-chemical quantities (e.g. compressibility, heat capacities, density, thermal expansivity, speed of sound) show anomalous behaviour. In this paper, several Widom lines of supercritical CO2 have been computed with the Wagner–Span reference equation of state. The locations of the Widom lines are compared with the P–T range of the Snøhvit, Sleipner, Nagaoka and Ketzin reservoirs, which are recently studied for their fitness for CO2 sequestration, and two natural CO2 storage analogues, Montmiral in France and Mihályi-Répcelak in Hungary. The potential consequences of leaking CO2 crossing any of the Widom lines are discussed.