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Vapor-Liquid Equilibrium

VLE calculations determine phase splits and compositions.

tip

The Raoult's Law VLE described below applies to Quick mode only. In Rigorous mode, VLE is handled by the selected equation of state (SRK, PR) using proper fugacity calculations, or by activity coefficient models (NRTL, UNIQUAC) for non-ideal liquid mixtures. Use rigorous mode for azeotropic, polar, or strongly non-ideal systems.

K-Value Calculation (Quick Mode)​

Using Raoult's Law:

Ki = Psat_i(T) / P

Vapor Pressure (Antoine)​

log₁₀(Psat) = A - B/(T + C)
export function getVaporPressure(componentId: string, T_K: number): number {
  const comp = componentData[componentId];
  if (!comp?.antoine) return 0;
  
  const [A, B, C] = comp.antoine;
  const T_C = T_K - 273.15;
  const P_mmHg = Math.pow(10, A - B / (T_C + C));
  return P_mmHg * 133.322; // Pa
}

Flash Calculation​

Rachford-Rice equation:

Σ zi(Ki - 1) / (1 + V(Ki - 1)) = 0

Limitations (Quick Mode)​

  • Ideal liquid solution (gamma = 1)
  • Ideal gas phase (phi = 1)
  • No azeotrope prediction

In rigorous mode, these limitations are removed. Cubic EOS models (SRK, PR) compute fugacity coefficients for both phases, and activity coefficient models (NRTL, UNIQUAC, eNRTL) capture liquid-phase non-ideality including azeotrope prediction.