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models.propulsion.feed_systems.tanks

machwave.models.propulsion.feed_systems.tanks

Tank

A generic two-phase tank model for any fluid recognized by CoolProp.

Assumptions
  • Constant temperature (isothermal).
  • Two-phase equilibrium if there's enough mass to form liquid + vapor.
  • If insufficient mass for liquid, treat it as an ideal gas.
  • Ignores temperature changes upon phase change (no thermal balance).
Source code in machwave/models/propulsion/feed_systems/tanks/base.py 
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class Tank:
    """
    A generic two-phase tank model for any fluid recognized by CoolProp.

    Assumptions:
      - Constant temperature (isothermal).
      - Two-phase equilibrium if there's enough mass to form liquid + vapor.
      - If insufficient mass for liquid, treat it as an ideal gas.
      - Ignores temperature changes upon phase change (no thermal balance).
    """

    def __init__(self, fluid_name, volume, temperature, initial_fluid_mass):
        """Initialize a two-phase tank model.

        Args:
            fluid_name: Name of the fluid in the CoolProp database
                (e.g. 'N2O', 'Oxygen', 'Hydrogen', 'Ethanol', etc.).
            volume: Internal volume of the tank [m^3].
            temperature: Absolute temperature [K], assumed constant.
            initial_fluid_mass: Initial total mass of fluid [kg].
        """
        self.fluid_name = fluid_name
        self.volume = volume
        self.temperature = temperature
        self.initial_fluid_mass = initial_fluid_mass
        self.fluid_mass = initial_fluid_mass

    def get_pressure(self) -> float:
        """Return the current tank pressure [Pa] using two-phase logic.

        1) Compute the saturation pressure at the given temperature.
        2) If fluid_mass > mass_if_all_vapor(p_sat), the tank is partially
           liquid and the pressure is pinned at saturation.
        3) Otherwise, the tank is all vapor (ideal gas), and we use
           P = (m / M) * R * T / V.

        Returns:
            Tank pressure [Pa].
        """
        # 1) Saturation pressure at the given T (if subcritical and property is defined).
        #    For cryogenics or other fluids, ensure T is within valid range for saturation data.
        p_sat = CP.PropsSI("P", "T", self.temperature, "Q", 0, self.fluid_name)

        # 2) Calculate how much mass we'd have if everything was vapor at p_sat.
        m_vap_max = self._mass_if_all_vapor(p_sat)

        if self.fluid_mass > m_vap_max:
            # We have enough mass that some fraction is liquid => saturation
            return p_sat
        else:
            # All vapor => ideal gas formula
            return self._pressure_if_ideal_gas(
                self.fluid_mass, self.volume, self.temperature
            )

    def get_density(self, pressure: float | None = None) -> float:
        """Return fluid density [kg/m^3] at tank pressure and temperature.

        Uses CoolProp. If pressure is provided, it is used as the tank
        pressure override (e.g., a piston-pressurized stacked-tank system).

        Returns:
            Fluid density [kg/m^3].
        """
        # Empty tank?
        if self.fluid_mass <= 0:
            return 0.0

        # 1) Current pressure (or override)
        p = self.get_pressure() if pressure is None else pressure

        try:
            # 2a) Single‐phase (or off‐saturation) density
            return CP.PropsSI("D", "T", self.temperature, "P", p, self.fluid_name)

        except ValueError:
            # 2b) Two‐phase: density at saturation is ambiguous, so compute mixture
            #    via quality:  x = m_vapor / m_total
            #    ρ_mix = 1 / ( x/ρ_v + (1−x)/ρ_l )

            # If we're exactly at saturation, infer quality by comparing against
            # max vapor mass at this pressure.
            m_vap_max = self._mass_if_all_vapor(p)

            if self.fluid_mass > m_vap_max:
                x = m_vap_max / self.fluid_mass
                rho_v = CP.PropsSI("D", "T", self.temperature, "Q", 1, self.fluid_name)
                rho_l = CP.PropsSI("D", "T", self.temperature, "Q", 0, self.fluid_name)
                return 1.0 / (x / rho_v + (1 - x) / rho_l)

            # Fallback: idealized bulk density
            return self.fluid_mass / self.volume

    def remove_propellant(self, mass: float) -> None:
        """
        Removes the specified mass of fluid [kg] from the tank.

        If the requested mass exceeds what's in the tank, sets total mass to 0.
        """
        if mass < 0:
            raise ValueError("Cannot remove a negative mass of propellant.")

        self.fluid_mass -= mass
        if self.fluid_mass < 0:
            self.fluid_mass = 0.0

    def _mass_if_all_vapor(self, p_vapor: float) -> float:
        """Return mass if tank were entirely vapor at given pressure.

        Uses ideal gas law at pressure p_vapor [Pa] and
        temperature self.temperature.

        Args:
            p_vapor: Pressure of the vapor [Pa].

        Returns:
            Mass of vapor [kg].
        """
        # Ideal gas:  m = (P * V * M) / (R_universal * T)
        molar_mass = CP.PropsSI("M", self.fluid_name)  # kg/mol
        R_universal = scipy.constants.R  # J/(mol*K)
        return (p_vapor * self.volume * molar_mass) / (R_universal * self.temperature)

    def _pressure_if_ideal_gas(
        self, mass: float, volume: float, temperature: float
    ) -> float:
        """
        Computes the pressure [Pa] if all the fluid is in the vapor phase,
        using the ideal gas law: P = (mass / M) * R * T / volume.
        """
        molar_mass = CP.PropsSI("M", self.fluid_name)  # kg/mol
        R_universal = scipy.constants.R  # J/(mol*K)
        n_moles = mass / molar_mass
        return (n_moles * R_universal * temperature) / volume

__init__(fluid_name, volume, temperature, initial_fluid_mass)

Initialize a two-phase tank model.

Parameters:

Name Type Description Default
fluid_name

Name of the fluid in the CoolProp database (e.g. 'N2O', 'Oxygen', 'Hydrogen', 'Ethanol', etc.).

 required
volume

Internal volume of the tank [m^3].

 required
temperature

Absolute temperature [K], assumed constant.

 required
initial_fluid_mass

Initial total mass of fluid [kg].

 required
Source code in machwave/models/propulsion/feed_systems/tanks/base.py 
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def __init__(self, fluid_name, volume, temperature, initial_fluid_mass):
    """Initialize a two-phase tank model.

    Args:
        fluid_name: Name of the fluid in the CoolProp database
            (e.g. 'N2O', 'Oxygen', 'Hydrogen', 'Ethanol', etc.).
        volume: Internal volume of the tank [m^3].
        temperature: Absolute temperature [K], assumed constant.
        initial_fluid_mass: Initial total mass of fluid [kg].
    """
    self.fluid_name = fluid_name
    self.volume = volume
    self.temperature = temperature
    self.initial_fluid_mass = initial_fluid_mass
    self.fluid_mass = initial_fluid_mass

get_density(pressure=None)

Return fluid density [kg/m^3] at tank pressure and temperature.

Uses CoolProp. If pressure is provided, it is used as the tank pressure override (e.g., a piston-pressurized stacked-tank system).

Returns:

Type Description
float

Fluid density [kg/m^3].
Source code in machwave/models/propulsion/feed_systems/tanks/base.py 
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def get_density(self, pressure: float | None = None) -> float:
    """Return fluid density [kg/m^3] at tank pressure and temperature.

    Uses CoolProp. If pressure is provided, it is used as the tank
    pressure override (e.g., a piston-pressurized stacked-tank system).

    Returns:
        Fluid density [kg/m^3].
    """
    # Empty tank?
    if self.fluid_mass <= 0:
        return 0.0

    # 1) Current pressure (or override)
    p = self.get_pressure() if pressure is None else pressure

    try:
        # 2a) Single‐phase (or off‐saturation) density
        return CP.PropsSI("D", "T", self.temperature, "P", p, self.fluid_name)

    except ValueError:
        # 2b) Two‐phase: density at saturation is ambiguous, so compute mixture
        #    via quality:  x = m_vapor / m_total
        #    ρ_mix = 1 / ( x/ρ_v + (1−x)/ρ_l )

        # If we're exactly at saturation, infer quality by comparing against
        # max vapor mass at this pressure.
        m_vap_max = self._mass_if_all_vapor(p)

        if self.fluid_mass > m_vap_max:
            x = m_vap_max / self.fluid_mass
            rho_v = CP.PropsSI("D", "T", self.temperature, "Q", 1, self.fluid_name)
            rho_l = CP.PropsSI("D", "T", self.temperature, "Q", 0, self.fluid_name)
            return 1.0 / (x / rho_v + (1 - x) / rho_l)

        # Fallback: idealized bulk density
        return self.fluid_mass / self.volume

get_pressure()

Return the current tank pressure [Pa] using two-phase logic.

1) Compute the saturation pressure at the given temperature. 2) If fluid_mass > mass_if_all_vapor(p_sat), the tank is partially liquid and the pressure is pinned at saturation. 3) Otherwise, the tank is all vapor (ideal gas), and we use P = (m / M) * R * T / V.

Returns:

Type Description
float

Tank pressure [Pa].
Source code in machwave/models/propulsion/feed_systems/tanks/base.py 
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def get_pressure(self) -> float:
    """Return the current tank pressure [Pa] using two-phase logic.

    1) Compute the saturation pressure at the given temperature.
    2) If fluid_mass > mass_if_all_vapor(p_sat), the tank is partially
       liquid and the pressure is pinned at saturation.
    3) Otherwise, the tank is all vapor (ideal gas), and we use
       P = (m / M) * R * T / V.

    Returns:
        Tank pressure [Pa].
    """
    # 1) Saturation pressure at the given T (if subcritical and property is defined).
    #    For cryogenics or other fluids, ensure T is within valid range for saturation data.
    p_sat = CP.PropsSI("P", "T", self.temperature, "Q", 0, self.fluid_name)

    # 2) Calculate how much mass we'd have if everything was vapor at p_sat.
    m_vap_max = self._mass_if_all_vapor(p_sat)

    if self.fluid_mass > m_vap_max:
        # We have enough mass that some fraction is liquid => saturation
        return p_sat
    else:
        # All vapor => ideal gas formula
        return self._pressure_if_ideal_gas(
            self.fluid_mass, self.volume, self.temperature
        )

remove_propellant(mass)

Removes the specified mass of fluid [kg] from the tank.

If the requested mass exceeds what's in the tank, sets total mass to 0.

Source code in machwave/models/propulsion/feed_systems/tanks/base.py 
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def remove_propellant(self, mass: float) -> None:
    """
    Removes the specified mass of fluid [kg] from the tank.

    If the requested mass exceeds what's in the tank, sets total mass to 0.
    """
    if mass < 0:
        raise ValueError("Cannot remove a negative mass of propellant.")

    self.fluid_mass -= mass
    if self.fluid_mass < 0:
        self.fluid_mass = 0.0