Thermal Properties

In This Topic

The drop-down list "Steam table" defines the steam table (IFC-67 or IAPWS-IF97) to be used for the calculation. The IAPWS-IF97 is used by default, and the IFC-67 is relevant only if the user wishes to reproduce the old results.

In addition, there is possible to calculate the properties of water/steam on the basis of splines. The LibSBTL also developed at the University Zittau/Görlitz is available for this. To use this library, “IAPWS-IF97 (SBTL)” has to be set as steam table in the Model Options under Simulation / Thermal Properties.

The two next entries ”Formulation gas table” and “Real gas correction“ affect the calculations on the line types Air, Flue gas, Gas, Crude gas, Coal, Oil, and User-defined fluid. In the ”Formulation gas table” you can choose between

• FDBR
• VDI4670
• LibHuGas (real Gas)
• NASA

When choosing VDI4670, the LibIdGas of Hochschule Zittau/Görlitz will be used for the substances N2, O2, Ne, Ar, CO, CO2, SO2, and H2O (see chapter Libraries of KCE ThermoFluidProperties.

If other substances are present on the line, these will be calculated according to FDBR.

When choosing LibHuGas (real gas), the LibHuGas will be used for the substances N2, O2, Ne, Ar, CO, CO2, SO2, and H2O, and the LibNH3 of Hochschule Zittau/Görlitz will be used for NH3. For CO2, the phase equilibrium will be calculated with the LibCO2. If liquid or solid CO2 is present, the CO2 fraction will be calculated with the LibCO2. All other substances in the line will be calculated according to FDBR.

FDBR, VDI4670 and NASA are methods based on an ideal gas approximation.

Here, the enthalpy of the gases depends only on the temperature. Only in the case of liquid water is there a slight dependence on pressure, because the calculation of the phase transition point is pressure-dependent.

Especially at higher pressures and lower temperatures, however, the ideal gas approximation is often too inaccurate. Therefore, it is possible to apply a real gas correction to the ideal gas calculation. Here you have the choice between:

no real gas correction (0)
real gas correction according to "Peng-Robinson, (PR)" (1)
real gas correction according to "Redlich-Kwong-Soave, (RKS)" (2)
real gas correction according to "Lee-Kessler-Ploecker, (LKP)" (3)
real gas correction according to "Redlich-Kwong, (RK)" (4)

In all settings, the following substances are treated specially:

Solids are always calculated according to FDBR, and there is no real gas correction for this.
However, there are certain options for setting the polynomial coefficients of the FDBR calculation:
- For “Ash“, a correction factor (specification value CPCORR in Component 1 and 33 respectively) can be specified, by which the calculated cp is multiplied. Depending on the line type, the setting of the flag FCOAL (in the case of Component 1 and 33 respectively), and the temperature, different polynomial coefficients are used here:
  - In the case of the line types “Oil (specifiable composition)“ and “User-defined fluid“ as well as in the case of all other line types if the flag FCOAL is set to “Old mode”:
    For T <= 1500°C:
    cp = (0.7133079 + 0.0019154204 * T – 3.494553e-6 * T² + 3.079276e-9 * T³ - 9.77527e-13 * T⁴) * CPCORR
    For T > 1500°C:
    cp = (1.104648 + 4.36052e-5 * T) * CPCORR
  - In all other cases:
    cp = (0.779413 + 0.002423974 * T + 4.676478e-8 * T² - 2.68897485e-9 * T³) * CPCORR

For the elementary analysis fraction (C,H,O,N,S,Cl), there are the following possible settings:
- In the case of the line type “User-defined fluid“, for T<=500°C the cp-coefficients a0, a1, a2, and a3 specified by the user are applied:
  cp = a0 + a1*T + a2*T² + a3*T³
  For T>500°C, cp is calculated with T=500°C.
- In the case of the line type “Oil“, the cp-coefficients are calculated as a function of the density (specification value RHOELEM) and multiplied by a correction factor (specification value ZFAC):
         a0 = (2.96 – 0.00133 * RHOELEM)*ZFAC
         a1 = (0.00615 – 0.0000023 * RHOELEM) *ZFAC
  For T<=500°C then applies:
         cp = a0 + a1*T
  For T>500°C:
         cp = a0 + a1 *500
- In the case of the other line types, the flag FCOAL serves to set different sets of polynomial coefficients. You can choose between
  - Old mode:
    For T <= 1500°C:
    cp = 0.6825314 + 0.003776748 * T – 4.278822e-6 * T² + 2.3451032e-9 * T³ - 5.21156e-13 * T⁴
    For T > 1500°C:
    cp = 1.515835 + 0.0003215344 * T
  - Hard coal:
    For T<=500°C:
    cp = (0.8137449 + 0.002530746639 * T + 4.882464e-8 * T² - 2.807419905e-9 * T³) * (1 + 0.95*VOLA),
    whereby VOLA is the fraction of the volatile substances specified in Component 1 and 33 respectively
    For T>500°C, cp is calculated with T=500°C.
  - Lignite
    For T<=500°C:
    cp = 1.577385 + 0.004905667 * T + 9.46431e-8 * T² - 5.44198e-9* T³
    For T>500°C, cp is calculated with T=500°C.

For water, the phase equilibrium is calculated at all times. As the calculation in ideal gas approximation is too inaccurate, the LibHuAirXiw (if the composition equals that of the air) or the LibHuGas is used for the phase equilibrium.
The gaseous fraction is calculated according to the selected ideal gas table, if applicable with real gas correction.
For the liquid and solid fraction respectively, a constant cp of 4.187 kJ/kgK (liquid) or 2.040 kJ/kgK (solid) is used.
When choosing “LibHuGas (real gas)“, a phase equilibrium is not only calculated for H2O but also for NH3 and CO2.

For more precise calculations, especially for considering phase equilibria for other substances as well, you can draw on other material properties libraries. This, however, does not happen model-wide but for individual lines by using the line type “2-Phase fluid” (liquid or gaseous), “Binary Mixture” or “Universal fluid”. The corresponding material properties libraries are then selected via Component 1 and 33 respectively (boundary or start value). See Chapter "Specification of Material Properties"

The combo box “Real gas correction“ is only active if one of the three ideal gas algorithms has been selected in the combo box ”Formulation gas table”. Then it allows either not to apply any real gas correction or one of the four mentioned above. This model specification then applies to all air, flue gas, gas, crude gas, coal, oil, and user-defined fluid lines of the model for which no special line-related settings have been made.

Line-related specification of the real gas correction:

Often there are only a few lines in the model for which the real gas correction is significant. The application to all lines (most of which probably have pressures in the range of the atmospheric pressure) is usually redundant and unnecessarily prolongs the computing time. For this reason, the real gas correction can also be defined in a line-specific way.

The individual specification of the real gas correction to be applied is effected in Component 1 and 33 respectively (boundary / start value) on the sheet “Material Fractions“. The definition is valid for the respective line and is then transferred along the main flow. On the line, you can see in the result value FREALGC which correction has been used. If two different real gas corrections meet in a mixer, a warning will be output.

Combo box ”Saltwater table”
Here you can choose between two versions of the sea water library LibSeaWa of Hochschule Zittau/Görlitz: the version from 2009 and the one from 2013. In addition, an older version of the salt water library is available for reasons of compatibility, which, however, should not be used for newer projects. This selection affects the lines of the type “Salt water“.

Combo box ”NCV calculation method”

This combo box serves to select the method for calculating the NCV of gases whose molecular composition is known.
You can choose between the following methods:

• 0: FDBR
• 1: ISO 6976
• 2: ASTM 3588

This flag corresponds to the model setting “ncvcalculationmethod“.
It is also possible to define the NCV calculation method line-specifically with Component 1 and 33 respectively.
This is done via the flag FNCVCALC.

For estimating the NCV for fuel fractions for which only the elementary analysis is known, other methods are relevant (see below, combo box ”NCV calculation method elementary").
See Chapter "Specification of Material Properties"

Input field ”NCV reference temperature”
Here the reference temperature for the NCV specification is defined. This reference temperature is uniformly taken as a basis for all NCV specifications in the model.

Please note: Component 46 (Measured value input): For specifying the NCV (FTYP=6), the user can select (FNCVREF) whether the reference temperature for the NCV is to be taken over from the model settings or if it is to be defined in the component itself in the reference value TNCVREF.

See Chapter "Specification of Material Properties"

Combo box ”NCV calculation method elementary”

This combo box serves to select the method for estimating the NCV of fuels for which only the elementary analysis is known.
You can choose between the following methods:

0: FDBR
1: Dulong
2: Boie
3: Grummel/Davis
4: Mott/Spooner
5: IGT
6: Seyler
7: Neavel
8: Given
9: Francis/Lloyd
10: Channiwala

Methods 1 to 10 all refer to the gross calorific value. This is then converted into the net calorific value by means of the evaporation enthalpy of the water.

This flag corresponds to the model setting “ncvcalculationmethodelementary“.
It is also possible to define the NCV calculation method line-specifically with Component 1 and 33 respectively.
This is done via the flag FNCVCALCELEM.

When specifying line-specific NCV calculation methods (both with FNCVCALC and with FNCVCALCELEM), this setting is then transferred in the direction of the flow and saved in the individual line for this purpose.
This applies accordingly to the reference temperature to which the NCV refers.
In mixers, the specifications of the main line (Inlet 1) are transferred to the outlet. If, in the modeling, lines with different specifications are to be joined, the line with the specifications that are to be retained therefore has to be connected to Pin 1.

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