rmgpy.thermo.NASA¶

class rmgpy.thermo.NASA(polynomials=None, Tmin=None, Tmax=None, E0=None, Cp0=None, CpInf=None, comment='')

A heat capacity model based on a set of one, two, or three NASAPolynomial objects. The attributes are:

Attribute Description
polynomials The list of NASA polynomials to use in this model
Tmin The minimum temperature in K at which the model is valid, or zero if unknown or undefined
Tmax The maximum temperature in K at which the model is valid, or zero if unknown or undefined
E0 The energy at zero Kelvin (including zero point energy)
comment Information about the model (e.g. its source)

The NASA polynomial is another representation of the heat capacity, enthalpy, and entropy using seven or nine coefficients $$\mathbf{a} = \left[a_{-2}\ a_{-1}\ a_0\ a_1\ a_2\ a_3\ a_4\ a_5\ a_6 \right]$$. The relevant thermodynamic parameters are evaluated via the expressions

$\frac{C_\mathrm{p}(T)}{R} = a_{-2} T^{-2} + a_{-1} T^{-1} + a_0 + a_1 T + a_2 T^2 + a_3 T^3 + a_4 T^4$
$\frac{H(T)}{RT} = - a_{-2} T^{-2} + a_{-1} T^{-1} \ln T + a_0 + \frac{1}{2} a_1 T + \frac{1}{3} a_2 T^2 + \frac{1}{4} a_3 T^3 + \frac{1}{5} a_4 T^4 + \frac{a_5}{T}$
$\frac{S(T)}{R} = -\frac{1}{2} a_{-2} T^{-2} - a_{-1} T^{-1} + a_0 \ln T + a_1 T + \frac{1}{2} a_2 T^2 + \frac{1}{3} a_3 T^3 + \frac{1}{4} a_4 T^4 + a_6$

In the seven-coefficient version, $$a_{-2} = a_{-1} = 0$$.

As simple polynomial expressions, the NASA polynomial is faster to evaluate when compared to the Wilhoit model; however, it does not have the nice physical behavior of the Wilhoit representation. Often multiple NASA polynomials are used to accurately represent the thermodynamics of a system over a wide temperature range.

Cp0

The heat capacity at zero temperature.

CpInf

The heat capacity at infinite temperature.

E0

The ground state energy (J/mol) at zero Kelvin, including zero point energy, or None if not yet specified.

Tmax

The maximum temperature at which the model is valid, or None if not defined.

Tmin

The minimum temperature at which the model is valid, or None if not defined.

changeBaseEnthalpy(self, double deltaH) → NASA

Add deltaH in J/mol to the base enthalpy of formation H298 and return the modified NASA object.

comment

comment: str

discrepancy(self, HeatCapacityModel other) → double

Return some measure of how dissimilar self is from other.

The measure is arbitrary, but hopefully useful for sorting purposes. Discrepancy of 0 means they are identical

getEnthalpy(self, double T) → double

Return the enthalpy $$H(T)$$ in J/mol at the specified temperature T in K.

getEntropy(self, double T) → double

Return the entropy $$S(T)$$ in J/mol*K at the specified temperature T in K.

getFreeEnergy(self, double T) → double

Return the Gibbs free energy $$G(T)$$ in J/mol at the specified temperature T in K.

getHeatCapacity(self, double T) → double

Return the constant-pressure heat capacity $$C_\mathrm{p}(T)$$ in J/mol*K at the specified temperature T in K.

isIdenticalTo(self, HeatCapacityModel other) → bool

Returns True if self and other report very similar thermo values for heat capacity, enthalpy, entropy, and free energy over a wide range of temperatures, or False otherwise.

isSimilarTo(self, HeatCapacityModel other) → bool

Returns True if self and other report similar thermo values for heat capacity, enthalpy, entropy, and free energy over a wide range of temperatures, or False otherwise.

isTemperatureValid(self, double T) → bool

Return True if the temperature T in K is within the valid temperature range of the thermodynamic data, or False if not. If the minimum and maximum temperature are not defined, True is returned.

poly1

poly1: rmgpy.thermo.nasa.NASAPolynomial

poly2

poly2: rmgpy.thermo.nasa.NASAPolynomial

poly3

poly3: rmgpy.thermo.nasa.NASAPolynomial

polynomials

The set of one, two, or three NASA polynomials.

selectPolynomial(self, double T) → NASAPolynomial
toCantera(self)

Return the cantera equivalent NasaPoly2 object from this NASA object.

toThermoData(self) → ThermoData

Convert the Wilhoit model to a ThermoData object.

toWilhoit(self) → Wilhoit

Convert a MultiNASA object multiNASA to a Wilhoit object. You must specify the linearity of the molecule linear, the number of vibrational modes Nfreq, and the number of hindered rotor modes Nrotors so the algorithm can determine the appropriate heat capacity limits at zero and infinite temperature.

Here is an example of a NASA entry:

    entry(
index = 2,
label = "octane",
molecule =
"""
1 C 0 {2,S}
2 C 0 {1,S} {3,S}
3 C 0 {2,S} {4,S}
4 C 0 {3,S} {5,S}
5 C 0 {4,S} {6,S}
6 C 0 {5,S} {7,S}
7 C 0 {6,S} {8,S}
8 C 0 {7,S}
""",
thermo = NASA(
polynomials = [
NASAPolynomial(coeffs=[1.25245480E+01,-1.01018826E-02,2.21992610E-04,-2.84863722E-07,1.12410138E-10,-2.98434398E+04,-1.97109989E+01], Tmin=(200,'K'), Tmax=(1000,'K')),
NASAPolynomial(coeffs=[2.09430708E+01,4.41691018E-02,-1.53261633E-05,2.30544803E-09,-1.29765727E-13,-3.55755088E+04,-8.10637726E+01], Tmin=(1000,'K'), Tmax=(6000,'K')),
],
Tmin = (200,'K'),
Tmax = (6000,'K'),
),
reference = Reference(authors=["check on burcat"], title='burcat', year="1999", url="http://www.me.berkeley.edu/gri-mech/version30/text30.html"),
referenceType = "review",
shortDesc = u"""""",
longDesc =
u"""

""",
)