71 lines
2.0 KiB
Python
71 lines
2.0 KiB
Python
# tests/cryo_tank/test_properties.py
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"""Tests for CoolProp property wrappers."""
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import pytest
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import sys
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sys.path.insert(0, "src")
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from cryo_tank.properties import (
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ln2_rho, ln2_h, ln2_u, ln2_T_from_u,
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ln2_drho_dT_const_p, ln2_du_dT_const_p,
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he_u, he_h, he_cp, he_cv,
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)
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from cryo_tank.config import P_WORKING
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class TestLN2Properties:
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"""Liquid nitrogen properties at P = 0.17 MPa."""
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def test_ln2_density_at_78K(self):
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rho = ln2_rho(78.0, P_WORKING)
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assert 800 < rho < 810 # ~803 kg/m3
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def test_ln2_enthalpy_at_77K(self):
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h = ln2_h(77.0, P_WORKING)
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assert -130000 < h < -110000 # ~-122695 J/kg
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def test_ln2_internal_energy_at_78K(self):
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u = ln2_u(78.0, P_WORKING)
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assert -130000 < u < -110000 # ~-120865 J/kg
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def test_ln2_T_from_u_roundtrip(self):
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T_orig = 78.0
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u = ln2_u(T_orig, P_WORKING)
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T_recovered = ln2_T_from_u(u, P_WORKING)
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assert abs(T_recovered - T_orig) < 0.01
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def test_ln2_density_derivative_matches_finite_difference(self):
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T = 78.0
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step = 1e-3
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actual = ln2_drho_dT_const_p(T, P_WORKING)
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expected = (
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ln2_rho(T + step, P_WORKING)
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- ln2_rho(T - step, P_WORKING)
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) / (2.0 * step)
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assert actual < 0.0
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assert abs(actual - expected) / abs(expected) < 1e-5
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def test_ln2_internal_energy_derivative_is_positive(self):
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du_dT = ln2_du_dT_const_p(78.0, P_WORKING)
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assert du_dT > 0.0
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class TestHeliumProperties:
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"""Helium properties."""
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def test_he_cp_near_5196(self):
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cp = he_cp()
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assert abs(cp - 5196.2) < 10
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def test_he_cv_near_3117(self):
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cv = he_cv()
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assert abs(cv - 3117.1) < 10
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def test_he_enthalpy_at_100K(self):
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h = he_h(100.0)
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# CoolProp gives ~524762 J/kg at 100K
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assert 500000 < h < 550000
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def test_he_internal_energy_at_78K(self):
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u = he_u(78.0)
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assert 200000 < u < 280000 # ~247932 J/kg
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