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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 when the Ideal property method is selected. Quick mode also supports PR (fugacity / phi-phi) and NRTL (activity / gamma-phi) for non-ideal systems. In Rigorous mode (DWSIM), VLE is handled by the selected DWSIM property package — cubic EOS (PR, SRK), activity (NRTL, UNIQUAC, UNIFAC), IAPWS-IF97 steam, or DWSIM electrolytes.

K-value calculation (Quick mode, Ideal)​

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 package)​

  • Ideal liquid solution (γ = 1)
  • Ideal gas phase (φ = 1)
  • No azeotrope prediction

Switch Quick mode to PR or NRTL to remove these limitations within the browser. For DWSIM's broader package set (SRK, UNIQUAC, UNIFAC, IAPWS-IF97 steam, electrolytes), switch to Rigorous mode.