Cantera
3.1.0a1
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Class for calculating the equation of state of water. More...
#include <WaterPropsIAPWS.h>
Class for calculating the equation of state of water.
This is a helper class for WaterSSTP and PDSS_Water and does not constitute a complete implementation of a thermo phase by itself (see Thermodynamic Properties and classes WaterSSTP and PDSS_Water).
The reference is W. Wagner, A. Pruss, "The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.
This class provides a very complicated polynomial for the specific Helmholtz free energy of water, as a function of temperature and density.
\[ \frac{M\hat{f}(\rho,T)}{R T} = \phi(\delta, \tau) = \phi^o(\delta, \tau) + \phi^r(\delta, \tau) \]
where
\[ \delta = \rho / \rho_c \quad \mathrm{and} \quad \tau = T_c / T \]
The following constants are assumed
\[ T_c = 647.096\mathrm{\;K} \]
\[ \rho_c = 322 \mathrm{\;kg\,m^{-3}} \]
\[ R/M = 0.46151805 \mathrm{\;kJ\,kg^{-1}\,K^{-1}} \]
The free energy is a unique single-valued function of the temperature and density over its entire range.
Note, the base thermodynamic state for this class is the one used in the steam tables, such that the liquid at the triple point for water has the following properties:
Therefore, to use this class within Cantera, offsets to u() and s() must be used to put the water class onto the same basis as other thermodynamic quantities. For example, in the WaterSSTP class, these offsets are calculated in the following way. The thermodynamic base state for water is set to the NIST basis here by specifying constants EW_Offset and SW_Offset. These offsets are calculated on the fly so that the following properties hold:
The offsets are calculated by actually computing the above quantities and then calculating the correction factor.
This class provides an interface to the WaterPropsIAPWSphi class, which actually calculates the \( \phi^o(\delta, \tau) \) and the \( \phi^r(\delta, \tau) \) polynomials in dimensionless form.
All thermodynamic results from this class are returned in dimensional form. This is because the gas constant (and molecular weight) used within this class is allowed to be potentially different than that used elsewhere in Cantera. Therefore, everything has to be in dimensional units. Note, however, the thermodynamic basis is set to that used in the steam tables. (u = s = 0 for liquid water at the triple point).
This class is not a ThermoPhase. However, it does maintain an internal state of the object that is dependent on temperature and density. The internal state is characterized by an internally stored \( \tau \) and a \( \delta \) value, and an iState value, which indicates whether the point is a liquid, a gas, or a supercritical fluid. Along with that the \( \tau \) and a \( \delta \) values are polynomials of \( \tau \) and a \( \delta \) that are kept by the WaterPropsIAPWSphi class. Therefore, whenever \( \tau \) or \( \delta \) is changed, the function setState() must be called in order for the internal state to be kept up to date.
The class is pretty straightforward. However, one function deserves mention. The density() function calculates the density that is consistent with a particular value of the temperature and pressure. It may therefore be multivalued or potentially there may be no answer from this function. It therefore takes a phase guess and a density guess as optional parameters. If no guesses are supplied to density(), a gas phase guess is assumed. This may or may not be what is wanted. Therefore, density() should usually at least be supplied with a phase guess so that it may manufacture an appropriate density guess. density() manufactures the initial density guess, nondimensionalizes everything, and then calls WaterPropsIAPWSphi::dfind(), which does the iterative calculation to find the density condition that matches the desired input pressure.
The phase guess defines are located in the .h file. they are
There are only three functions which actually change the value of the internal state of this object after it's been instantiated
The setState_TD() is the main function that sets the temperature and rho value. The density() function serves as a setState_TP() function, in that it sets internal state to a temperature and pressure. However, note that this is potentially multivalued. Therefore, we need to supply in addition a phase guess and a rho guess to the input temperature and pressure. The psat() function sets the internal state to the saturated liquid or saturated gas state, depending on the waterState parameter.
Because the underlying object WaterPropsIAPWSphi is privately held, you can be sure that the underlying state of this object doesn't change except due to the three function calls listed above.
Definition at line 161 of file WaterPropsIAPWS.h.
Public Member Functions | |
WaterPropsIAPWS ()=default | |
Base constructor. More... | |
WaterPropsIAPWS (const WaterPropsIAPWS &right)=delete | |
WaterPropsIAPWS & | operator= (const WaterPropsIAPWS &right)=delete |
void | setState_TD (double temperature, double rho) |
Set the internal state of the object wrt temperature and density. More... | |
double | gibbs_mass () const |
Get the Gibbs free energy (J/kg) at the current temperature and density. More... | |
double | enthalpy_mass () const |
Get the enthalpy (J/kg) at the current temperature and density. More... | |
double | intEnergy_mass () const |
Get the internal energy (J/kg) at the current temperature and density. More... | |
double | entropy_mass () const |
Get the entropy (J/kg/K) at the current temperature and density. More... | |
double | cv_mass () const |
Get the constant volume heat capacity (J/kg/K) at the current temperature and density. More... | |
double | cp_mass () const |
Get the constant pressure heat capacity (J/kg/K) at the current temperature and density. More... | |
double | pressure () const |
Calculates the pressure (Pascals), given the current value of the temperature and density. More... | |
double | density (double temperature, double pressure, int phase=-1, double rhoguess=-1.0) |
Calculates the density given the temperature and the pressure, and a guess at the density. More... | |
double | density_const (double pressure, int phase=-1, double rhoguess=-1.0) const |
Calculates the density given the temperature and the pressure, and a guess at the density, while not changing the internal state. More... | |
double | density () const |
Returns the density (kg m-3) More... | |
double | temperature () const |
Returns the temperature (Kelvin) More... | |
double | coeffThermExp () const |
Returns the coefficient of thermal expansion. More... | |
double | coeffPresExp () const |
Returns the isochoric pressure derivative wrt temperature. More... | |
double | isothermalCompressibility () const |
Returns the coefficient of isothermal compressibility for the state of the object. More... | |
double | dpdrho () const |
Returns the value of dp / drho at constant T for the state of the object. More... | |
double | psat_est (double temperature) const |
This function returns an estimated value for the saturation pressure. More... | |
double | psat (double temperature, int waterState=WATER_LIQUID) |
This function returns the saturation pressure given the temperature as an input parameter, and sets the internal state to the saturated conditions. More... | |
double | densSpinodalWater () const |
Return the value of the density at the water spinodal point (on the liquid side) for the current temperature. More... | |
double | densSpinodalSteam () const |
Return the value of the density at the water spinodal point (on the gas side) for the current temperature. More... | |
int | phaseState (bool checkState=false) const |
Returns the Phase State flag for the current state of the object. More... | |
double | Tcrit () const |
Returns the critical temperature of water (Kelvin) More... | |
double | Pcrit () const |
Returns the critical pressure of water (22.064E6 Pa) More... | |
double | Rhocrit () const |
Return the critical density of water (kg m-3) More... | |
Private Member Functions | |
void | calcDim (double temperature, double rho) |
Calculate the dimensionless temp and rho and store internally. More... | |
void | corr (double temperature, double pressure, double &densLiq, double &densGas, double &delGRT) |
Utility routine in the calculation of the saturation pressure. More... | |
void | corr1 (double temperature, double pressure, double &densLiq, double &densGas, double &pcorr) |
Utility routine in the calculation of the saturation pressure. More... | |
Private Attributes | |
WaterPropsIAPWSphi | m_phi |
pointer to the underlying object that does the calculations. More... | |
double | tau = -1.0 |
Dimensionless temperature, tau = T_C / T. More... | |
double | delta = -1.0 |
Dimensionless density, delta = rho / rho_c. More... | |
int | iState = -30000 |
Current state of the system. More... | |
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default |
Base constructor.
void setState_TD | ( | double | temperature, |
double | rho | ||
) |
Set the internal state of the object wrt temperature and density.
temperature | temperature (kelvin) |
rho | density (kg m-3) |
Definition at line 548 of file WaterPropsIAPWS.cpp.
double gibbs_mass | ( | ) | const |
Get the Gibbs free energy (J/kg) at the current temperature and density.
Definition at line 554 of file WaterPropsIAPWS.cpp.
double enthalpy_mass | ( | ) | const |
Get the enthalpy (J/kg) at the current temperature and density.
Definition at line 559 of file WaterPropsIAPWS.cpp.
double intEnergy_mass | ( | ) | const |
Get the internal energy (J/kg) at the current temperature and density.
Definition at line 564 of file WaterPropsIAPWS.cpp.
double entropy_mass | ( | ) | const |
Get the entropy (J/kg/K) at the current temperature and density.
Definition at line 569 of file WaterPropsIAPWS.cpp.
double cv_mass | ( | ) | const |
Get the constant volume heat capacity (J/kg/K) at the current temperature and density.
Definition at line 574 of file WaterPropsIAPWS.cpp.
double cp_mass | ( | ) | const |
Get the constant pressure heat capacity (J/kg/K) at the current temperature and density.
Definition at line 579 of file WaterPropsIAPWS.cpp.
double pressure | ( | ) | const |
Calculates the pressure (Pascals), given the current value of the temperature and density.
The density is an independent variable in the underlying equation of state
Definition at line 46 of file WaterPropsIAPWS.cpp.
double density | ( | double | temperature, |
double | pressure, | ||
int | phase = -1 , |
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double | rhoguess = -1.0 |
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) |
Calculates the density given the temperature and the pressure, and a guess at the density.
Sets the internal state.
Note, below T_c, this is a multivalued function.
The density() function calculates the density that is consistent with a particular value of the temperature and pressure. It may therefore be multivalued or potentially there may be no answer from this function. It therefore takes a phase guess and a density guess as optional parameters. If no guesses are supplied to density(), a gas phase guess is assumed. This may or may not be what is wanted. Therefore, density() should usually at least be supplied with a phase guess so that it may manufacture an appropriate density guess. density() manufactures the initial density guess, nondimensionalizes everything, and then calls WaterPropsIAPWSphi::dfind(), which does the iterative calculation to find the density condition that matches the desired input pressure.
temperature | Kelvin |
pressure | Pressure in Pascals (Newton/m**2) |
phase | guessed phase of water; -1: no guessed phase |
rhoguess | guessed density of the water; -1.0 no guessed density |
Definition at line 54 of file WaterPropsIAPWS.cpp.
double density_const | ( | double | pressure, |
int | phase = -1 , |
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double | rhoguess = -1.0 |
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) | const |
Calculates the density given the temperature and the pressure, and a guess at the density, while not changing the internal state.
Note, below T_c, this is a multivalued function.
The density() function calculates the density that is consistent with a particular value of the temperature and pressure. It may therefore be multivalued or potentially there may be no answer from this function. It therefore takes a phase guess and a density guess as optional parameters. If no guesses are supplied to density(), a gas phase guess is assumed. This may or may not be what is wanted. Therefore, density() should usually at least be supplied with a phase guess so that it may manufacture an appropriate density guess. density() manufactures the initial density guess, nondimensionalizes everything, and then calls WaterPropsIAPWSphi::dfind(), which does the iterative calculation to find the density condition that matches the desired input pressure.
pressure | Pressure in Pascals (Newton/m**2) |
phase | guessed phase of water; -1: no guessed phase |
rhoguess | guessed density of the water; -1.0: no guessed density |
Definition at line 114 of file WaterPropsIAPWS.cpp.
double density | ( | ) | const |
Returns the density (kg m-3)
The density is an independent variable in the underlying equation of state
Definition at line 167 of file WaterPropsIAPWS.cpp.
double temperature | ( | ) | const |
Returns the temperature (Kelvin)
Definition at line 172 of file WaterPropsIAPWS.cpp.
double coeffThermExp | ( | ) | const |
Returns the coefficient of thermal expansion.
alpha = d (ln V) / dT at constant P.
Definition at line 234 of file WaterPropsIAPWS.cpp.
double coeffPresExp | ( | ) | const |
Returns the isochoric pressure derivative wrt temperature.
beta = M / (rho * Rgas) (d (pressure) / dT) at constant rho
Note for ideal gases this is equal to one.
beta = delta (phi0_d() + phiR_d()) - tau delta (phi0_dt() + phiR_dt())
Definition at line 229 of file WaterPropsIAPWS.cpp.
double isothermalCompressibility | ( | ) | const |
Returns the coefficient of isothermal compressibility for the state of the object.
kappa = - d (ln V) / dP at constant T.
units - 1/Pascal
Definition at line 215 of file WaterPropsIAPWS.cpp.
double dpdrho | ( | ) | const |
Returns the value of dp / drho at constant T for the state of the object.
units - Joules / kg
Definition at line 222 of file WaterPropsIAPWS.cpp.
double psat_est | ( | double | temperature | ) | const |
This function returns an estimated value for the saturation pressure.
It does this via a polynomial fit of the vapor pressure curve. units = (Pascals)
temperature | Input temperature (Kelvin) |
Definition at line 177 of file WaterPropsIAPWS.cpp.
double psat | ( | double | temperature, |
int | waterState = WATER_LIQUID |
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) |
This function returns the saturation pressure given the temperature as an input parameter, and sets the internal state to the saturated conditions.
Note this function will return the saturation pressure, given the temperature. It will then set the state of the system to the saturation condition. The input parameter waterState is used to either specify the liquid state or the gas state at the desired temperature and saturated pressure.
If the input temperature, T, is above T_c, this routine will set the internal state to T and the pressure to P_c. Then, return P_c.
temperature | input temperature (kelvin) |
waterState | integer specifying the water state |
Definition at line 291 of file WaterPropsIAPWS.cpp.
double densSpinodalWater | ( | ) | const |
Return the value of the density at the water spinodal point (on the liquid side) for the current temperature.
Definition at line 373 of file WaterPropsIAPWS.cpp.
double densSpinodalSteam | ( | ) | const |
Return the value of the density at the water spinodal point (on the gas side) for the current temperature.
Definition at line 461 of file WaterPropsIAPWS.cpp.
int phaseState | ( | bool | checkState = false | ) | const |
Returns the Phase State flag for the current state of the object.
checkState | If true, this function does a complete check to see where in parameters space we are |
There are three values:
Definition at line 333 of file WaterPropsIAPWS.cpp.
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inline |
Returns the critical temperature of water (Kelvin)
This is hard coded to the value 647.096 Kelvin
Definition at line 370 of file WaterPropsIAPWS.h.
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inline |
Returns the critical pressure of water (22.064E6 Pa)
This is hard coded to the value of 22.064E6 pascals
Definition at line 378 of file WaterPropsIAPWS.h.
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inline |
Return the critical density of water (kg m-3)
This is equal to 322 kg m-3.
Definition at line 386 of file WaterPropsIAPWS.h.
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private |
Calculate the dimensionless temp and rho and store internally.
temperature | input temperature (kelvin) |
rho | density in kg m-3 |
Definition at line 29 of file WaterPropsIAPWS.cpp.
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private |
Utility routine in the calculation of the saturation pressure.
Calculate the Gibbs free energy in mks units of J kmol-1 K-1.
temperature | temperature (kelvin) |
pressure | pressure (Pascal) |
densLiq | Output density of liquid |
densGas | output Density of gas |
delGRT | output delGRT |
Definition at line 242 of file WaterPropsIAPWS.cpp.
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private |
Utility routine in the calculation of the saturation pressure.
temperature | temperature (kelvin) |
pressure | pressure (Pascal) |
densLiq | Output density of liquid |
densGas | output Density of gas |
pcorr | output corrected pressure |
Definition at line 266 of file WaterPropsIAPWS.cpp.
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mutableprivate |
pointer to the underlying object that does the calculations.
Definition at line 423 of file WaterPropsIAPWS.h.
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private |
Dimensionless temperature, tau = T_C / T.
Definition at line 426 of file WaterPropsIAPWS.h.
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mutableprivate |
Dimensionless density, delta = rho / rho_c.
Definition at line 429 of file WaterPropsIAPWS.h.
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mutableprivate |
Current state of the system.
Definition at line 432 of file WaterPropsIAPWS.h.