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Validation: src/janus/utils/cp_funcs.py

This page tracks the reference_pinned test that anchors the per-species molar heat capacity cpv in janus.utils.cp_funcs against the NIST-JANAF thermochemical tables.

Test id Reference Anchor type Scope
tests/utils/test_cp_funcs.py::test_water_heat_capacity_matches_nist_shomate_at_500K NIST-JANAF Thermochemical Tables1 Published benchmark Pins the temperature-dependent Shomate branch for gaseous water to 35.22 J/mol/K at 500 K and verifies the heat capacity rises with temperature as vibrational modes activate.

Re-derivation note

cpv(vol, tmp, cp_mode) dispatches between a flat constant heat capacity (cp_mode = "constant") and the NIST Shomate polynomial (cp_mode = "T-dependent"). The Shomate branch evaluates Cp = A + B t + C t^2 + D t^3 + E / t^2 with t = T / 1000 and the tabulated water-vapour coefficients. At 500 K the tabulated molar heat capacity of gaseous water is 35.22 J/mol/K; the implementation returns 35.218, pinned to rel=2e-3.

The value 35.22 J/mol/K distinguishes the Shomate branch from the flat constant branch, which does not rise with temperature. The scale guard 25 < cp < 55 J/mol/K rejects a per-gram versus per-mole unit slip (which would land near 3.5 J/g/K numerically) or a factor-of-ten error. An unknown species with no table entry returns 0.0 in both branches, the guard path exercised separately.

Anchor type

Published benchmark (NIST-JANAF Shomate water-vapour coefficients). Positivity of a known species' heat capacity and rough constant-versus-Shomate agreement for CO2 are asserted as the physics invariants.

Cross-references

  • src/janus/utils/cp_funcs.py: cpv.
  • The cp_mode string selects the branch; a caller that relies on the default without naming the mode it needs is a review red flag, since a default flip silently redirects every implicit caller.

References

  1. M. W. Chase, NIST-JANAF Thermochemical Tables, 4th edition, Journal of Physical and Chemical Reference Data, Monograph 9, 1998. Machine-readable Shomate coefficients for individual species are available through the NIST Chemistry WebBook. ↩