test_props_near_dome.py

Go to the documentation of this file.

"""The tables are not trusted near the saturation line (``backends.coolprop._Dome``).
 
CoolProp's bicubic tables interpolate across the saturation line wherever a
table cell straddles it. Measured against the equation of state (HEOS), on
CoolProp 7.2 and 8.0: nitrogen ten kelvin above its boiling point at 1.07 bar
read 83 kg/m^3 for 4.3; saturated oxygen vapour at 90 K read 0.47 bar for
0.99 -- the partial pressure a cold LOX ullage is built from. Near the line the
tables now decline and the chain's HEOS answers; away from it nothing changes.
These are checked against CoolProp's HEOS directly, not against feedtwin.
"""
 
from __future__ import annotations
 
import CoolProp.CoolProp as CP
import pytest
 
from feedtwin.props import Fluid
 
N2 = Fluid("nitrogen")
O2 = Fluid("oxygen")
 
 
@pytest.mark.parametrize("above_K", [0.5, 2.0, 5.0, 10.0])
def test_cold_nitrogen_near_an_atmosphere_is_a_gas(above_K: float) -> None:
    p = 107613.0
    T = CP.PropsSI("T", "P", p, "Q", 1, "Nitrogen") + above_K
    assert N2.get("rho", p=p, T=T) == pytest.approx(
        CP.PropsSI("D", "P", p, "T", T, "Nitrogen"), rel=1e-3
    )
 
 
@pytest.mark.parametrize("T", [90.0, 110.0, 140.0])
def test_saturated_oxygen_vapour_has_its_own_pressure(T: float) -> None:
    rho = CP.PropsSI("D", "T", T, "Q", 1, "Oxygen")
    assert O2.get("p", rho=rho, T=T) == pytest.approx(
        CP.PropsSI("P", "D", rho, "T", T, "Oxygen"), rel=1e-3
    )
 
 
def test_a_vent_gas_temperature_from_its_enthalpy() -> None:
    p = 2.2e5
    T = CP.PropsSI("T", "P", p, "Q", 1, "Nitrogen") + 1.0
    h = CP.PropsSI("H", "P", p, "T", T, "Nitrogen")
    assert N2.get("T", p=p, h=h) == pytest.approx(T, abs=0.02)
 
 
@pytest.mark.parametrize(
    "T,p",
    [(144.0, 5.0e6), (148.5, 5.0e6), (144.0, 6.0e6), (140.0, 6.0e6)],
)
def test_just_past_the_critical_band_the_tables_are_not_trusted(
    T: float, p: float
) -> None:
    """Nitrogen just outside the old band (0.75-1.5 p_c, below T_c + 16 K)
    read density 3.7 % off, cp 9.4 %, cp/cv 14 % and viscosity 15 % at these
    points. The band reaches 2.5 p_c and T_c + 30 K now; HEOS answers there."""
    for key, prop in (("rho", "D"), ("cp", "C"), ("mu", "V")):
        assert N2.get(key, p=p, T=T) == pytest.approx(
            CP.PropsSI(prop, "P", p, "T", T, "Nitrogen"), rel=1e-3
        ), key
    gamma = CP.PropsSI("C", "P", p, "T", T, "Nitrogen") / CP.PropsSI(
        "O", "P", p, "T", T, "Nitrogen"
    )
    assert N2.get("gamma", p=p, T=T) == pytest.approx(gamma, rel=1e-3)
 
 
def test_away_from_the_line_the_tables_still_answer() -> None:
    """The guard costs nothing where the tables are good: warm pressurant and
    subcooled LOX at tank pressure stay on the fast backend."""
    assert N2.state(p=3.0e7, T=293.15).backend == "bicubic"
    assert O2.state(p=3.7e6, T=90.0).backend == "bicubic"
    assert N2.state(p=107613.0, T=82.0).backend == "heos"