Highly Accurate Equations of State for Pure Fluids

Accurate knowledge of thermodynamic properties is essential for the design and optimization of any process in energy and process engineering. They also play an essential role in academic research. Nowadays, these properties are mainly calculated with the help of equations of state, which are usually generated based on experimentally determined property data (e.g. pressure, density, heat capacity, sound velocity, etc.). If such equations are available, they can be implemented in property software packages such as TREND, REFPROP or CoolProp, allowing the user to calculate the required property data at any time and at (theoretically) arbitrary state points.

Equations of State for Mixtures

The development and simulation of energy technology processes requires the accurate calculation of thermophysical properties. In most applications, the working fluid is not a pure fluid but a mixture of several substances. These are often non-ideal and exhibit complex phase equilibria. Therefore, highly accurate equations of state for mixtures in the form of the Helmholtz energy are required. These fundamental equations allow the calculation of all thermophysical properties in gaseous, liquid, supercritical, and saturation states.

Equations of State Based on Hybrid Data Sets

In addition to conventionally measured property data, data sets from molecular simulations can be used to develop equations of state. This is particularly interesting for fluids and state regions that are difficult or impossible to address experimentally. At the same time, the molecular models can be further improved by comparison with equations of state of well-measured fluids.

Calculation of Complex Phase Equilibria Using Highly Accurate Equations of State

In the context of carbon dioxide capture and sequestration, the focus in the field of thermodynamic property data research has so far been on pipeline transport. However, due to the injection of the sequestered carbon dioxide in saline aquifers, an additional model is necessary, which enables a consistent description of the transport and storage section. The material properties of the brines in the aquifers differ significantly from those of pure water, which were used in the equation models developed up to now.

Phase Equilibria Including Hydrates

In addition to phase equilibria between liquid and gaseous phases, phase equilibria with solid phases also play a major role in many technical applications. In systems conaiting water, hydrate formation is important to condsider. In many areas of the natural gas and petroleum industries, hydrate formation is feared because it can lead to the clogging of pipelines and valves by ice-like structures even at temperatures well above 0 °C. Hydrate formation is also frequently used as a storage medium for liquids and gases. However, hydrates are often discussed as storage options for the transport of gases or as reservoirs for large quantities of methane. Methane hydrates play a major role in geology and atmospheric research; their melting can destabilize continental shelves and release dangerous amounts of methane into the atmosphere.