Sets and Points in the Dortmund Data Bank
How experimental data are organized
The Dortmund Data Bank mainly contains experimental data only, with few exceptions. Data sets and points are organized according to typical experiments. This means that normally all values measured or given in a single measurement are combined in a data point.
- VLE – Vapor-liquid equilibria: The temperature (T), pressure (P), and the compositions of the liquid (x) and vapor (y) phase typically form a data point. Several measurement methods do not deliver all these four readings and so some data point may only contain, e.g., P-x-T or T-x-y data.
- SLE – Solid-liquid equilibria: A SLE data point contains the melting temperature and at least the composition of the liquid phase (xl), sometimes also a pressure or the composition of the solid phase (xs) for non-eutectic systems.
- LLE – Liquid-liquid equilibria: These data describe miscibility gaps. A data point contains at least a temperature and the composition of a single phase (xl,1). If the data point represents a tie line a second composition of the other phase (xl,2) is also given. The data point may additionally contain a vapor composition (VLLE – vapor-liquid-liquid equilibrium).
Several such points form a data set. In most cases these points have been measured in one single experiment under the same conditions. This typically means:
- Always the same component or components – a data set always contains data for a single mixture or a single pure component.
- Often a constant property. For VLE it is a common procedure to measure several points at different compositions but at the same pressure (isobaric measurement) or temperature (isothermal measurement).
In the Dortmund Data Bank there are some exceptions to these basic rules:
- Activity coefficients at infinite dilution (ACT) are always stored as single points. It is the same for (a)zeotropic data (AZD). The latter are often derived from VLE data sets, either by the author or by DDBST staff, and describe therefore the azeotropic point obtained from a single VLE set.
- A few sets may be organized differently due to data bank format issues or historic reasons.