Thermodynamic Interfaces

Cantera

rgfrosh has native support for cantera.ThermoPhase instances. As of the Cantera 3.0 release, real gas equations of state are also supported.

CoolProp

The CPInterface wrapper is provided to enable straightforward use of CoolProp.AbstractState instances with rgfrosh:

from rgfrosh import FrozenShock
from rgfrosh.thermo import CPInterface
import CoolProp as CP

state = CP.AbstractState("PR", "Argon")  # Peng-Robinson
state.specify_phase(CP.iphase_supercritical_gas)  # (1)!

shock = FrozenShock(CPInterface(state), u1=763, T1=293, P1=(10 * 101325))

1. Specifying phase is necessary if the cubic has three roots

User-defined Interfaces

If you would like to use rgfrosh with thermodynamic routines other than Cantera or CoolProp, all you have to do is pass an object that matches the pattern defined by the ThermoInterface class.

Note

The ThermoInterface class utilizes structural subtyping (see PEP 544) through the built-in typing.Protocol base class. Thus, any class that implements the required methods is considered a subtype, even if it is not an explicit subclass of ThermoInterface; however, explicitly subclassing ThermoInterface is recommended for user-defined interfaces to ensure all required methods are defined.

Below is a simple example implementation of an interface for a calorically perfect gas:

from rgfrosh import ThermoInterface
from rgfrosh.constants import GAS_CONSTANT


class PerfectGas(ThermoInterface):
    """Thermo interface for a calorically perfect gas."""

    def __init__(self, gamma, MW):
        self._T = 300
        self._P = 101325
        self.gamma = gamma
        self.MW = MW

    @property
    def TP(self):
        return self._T, self._P

    @TP.setter
    def TP(self, value):
        self._T, self._P = value

    @property
    def mean_molecular_weight(self):
        return self.MW

    @property
    def density_mass(self):
        return self._P / (GAS_CONSTANT / self.MW * self._T)

    @property
    def cp_mass(self):
        return self.gamma / (self.gamma - 1) * GAS_CONSTANT / self.MW

    @property
    def enthalpy_mass(self):
        return self.cp_mass * self._T

    @property
    def isothermal_compressibility(self):
        return 1 / self._P

    @property
    def thermal_expansion_coeff(self):
        return 1 / self._T

The interface can then be used with FrozenShock:

from rgfrosh import FrozenShock

argon = PerfectGas(5/3, 40)
frozen_shock = FrozenShock(argon, u1=750, P1=101325)

print(f"T5 = {frozen_shock.T5:.1f} K, P5 = {frozen_shock.P5 / 101325:.2f} atm")

which yields the reflected shock conditions:

T5 = 1353.9 K, P5 = 23.60 atm

For the case of a calorically perfect gas, the frozen shock solution should simplify to the ideal shock solution. We can use the custom interface with the IdealShock.from_thermo classmethod to verify this:

from rgfrosh import IdealShock

ideal_shock = IdealShock.from_thermo(argon, u1=750, P1=101325)

print(f"T5 = {frozen_shock.T5:.1f} K, P5 = {frozen_shock.P5 / 101325:.2f} atm")

which yields approximately the same solution:

T5 = 1353.9 K, P5 = 23.60 atm