Database

The SQLite database stores NASA polynomial coefficients for each species in a normalised three-table schema.

Database Schema

The database contains three linked tables:

species — chemical species metadata

  • id — primary key (auto-increment)

  • name — species name (e.g., 'CH4', 'CO2')

  • formula — chemical formula

  • phase — 'gas' or 'condensed'

  • molecular_weight — in g/mol

  • heat_of_formation_298K — ΔH°f at 298.15 K in J/mol

  • num_intervals — number of temperature intervals

  • comments — free-text notes

temperature_intervals — one row per temperature range per species

  • id — primary key

  • species_id — foreign key → species.id

  • interval_number — 1, 2, 3, …

  • temp_min — minimum valid temperature [K]

  • temp_max — maximum valid temperature [K]

  • h_298_to_0 — H°(298.15) − H°(0) in J/mol

coefficients — NASA-7 polynomial coefficients (one row per interval)

  • id — primary key

  • interval_id — foreign key → temperature_intervals.id

  • a1 … a7 — polynomial coefficients

  • b1, b2 — integration constants

metadata — additive dataset metadata

  • key — metadata key

  • value — metadata value

Newly built NASA Glenn/CEA databases store gas_constant_ref = 8.314510 and its provenance in this table. Legacy databases without this table remain readable and use the universal fallback constant.

NASA Polynomial Format

pyglenn uses the alternate NASA-7 form (also known as the “old” or “Gordon–McBride” form). The dimensionless properties are:

\[\frac{C_p^\circ}{R} = \frac{a_1}{T^2} + \frac{a_2}{T} + a_3 + a_4 T + a_5 T^2 + a_6 T^3 + a_7 T^4\]
\[\frac{H^\circ}{RT} = -\frac{a_1}{T^2} + a_2\frac{\ln T}{T} + a_3 + a_4\frac{T}{2} + a_5\frac{T^2}{3} + a_6\frac{T^3}{4} + a_7\frac{T^4}{5} + \frac{b_1}{T}\]
\[\frac{S^\circ}{R} = -\frac{a_1}{2T^2} - \frac{a_2}{T} + a_3 \ln T + a_4 T + a_5\frac{T^2}{2} + a_6\frac{T^3}{3} + a_7\frac{T^4}{4} + b_2\]

These match the implementation in pyglenn.database (calculate_cp(), calculate_h(), calculate_s()).

Querying the Database

You can query the database directly using ThermoDBQuery:

from pyglenn import ThermoDBQuery

query = ThermoDBQuery('thermo.db')
query.connect()

# Search species by name
species = query.find_species('CH4', exact_match=True)
print(species[0].name, species[0].phase)

# Get complete data (metadata + all intervals + coefficients)
data = query.get_species_data(species[0].id)
for interval in data.intervals:
    print(f"  {interval.temp_min}–{interval.temp_max} K")
    coeffs = interval.coefficients
    print(f"  a1={coeffs.a1}, …, a7={coeffs.a7}")

query.close()

Gas Constants

The universal CODATA gas constant and the NASA Glenn/CEA dataset reference constant are available as pyglenn.R_UNIVERSAL and pyglenn.R_GLENN. pyglenn.R remains a compatibility alias for the universal value.

from pyglenn import R_GLENN, R_UNIVERSAL

print(f"R (universal) = {R_UNIVERSAL} J/(mol·K)")
print(f"R (NASA Glenn) = {R_GLENN} J/(mol·K)")