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State Determination Steam/Condensate

State Determination Steam/Condensate

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State Determination Component

The State Determination component is used for modeling energy systems with the material model MM_Steam. It serves to clearly determine the thermodynamic state of the medium water.

Component Template

The component template State_Determination.e-ctpl is located in the Component template library folder Steam Supply.

Integration Into a Scheme

The following figure shows the scheme from Tutorial 32 as an example.

You can also see how the component is connected in the article Special Features Steam.

Thermodynamic States

With the State Determination component, the medium water is modeled in three possible thermodynamic states with the material model MM_Steam: liquid, vaporous, and as a mixed form in the wet steam region.

For an unambiguous determination of a condition, the specification of two variables is always necessary.

For single-phase liquid or vaporous media, the state can be determined, for example, by specifying pressure and temperature. The Temperature can be expressed in Absolute terms or as a positive or negative deviation from the saturation temperature in the form of Superheating steam or Supercooling condensate. Of course, other specifications are theoretically possible, such as specific enthalpy and entropy. However, these are not directly measurable and are therefore not used in this model to characterize a state.

The wet steam region describes the state in which the water is neither purely liquid nor purely vaporous. In this range, the combination of pressure and temperature cannot be used to clearly determine a condition, since pressure and temperature are constant.

For example, if boiling hot water is evaporated at 1 atm and 100 °C, the pressure and temperature remain constant for a while. The energy supplied ensures that the steam content in the mixture increases. Only after the liquid has completely passed into the vapour phase does the temperature increase further.

From an energy point of view, the exact state can therefore only be determined by specifying the pressure and steam content or the temperature and steam content. Theoretically, the specification of specific enthalpy and entropy would also be possible, but both are not used for modeling in TOP-Energy.

Modeling in TOP-Energy

In TOP-Energy the specification of the absolute Pressure is necessary.

The second setting can be selected from the drop-down menu (see following figure).

The temperature difference to the saturation point (Superheating steam or Supercooling condensate), the Absolute temperature or the Steam mass fraction can be specified if a condition in the wet steam region is to be mapped.

  • Absolute temperature: State is calculated (wet steam, steam, condensate).
  • Supercooling condensate: Insert the temperature difference to saturation temperature (condensate).
  • Superheating steam: Insert the temperature difference to saturation temperature (steam).
  • Steam mass fraction: Insert the ratio of vaporous share to total mass (wet steam).

The remaining state variables are calculated and displayed in the Output data (see following figure).

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