sandbox/ecipriano/src/thermodynamics.h

Thermodynamics functions

Collection of thermodynamics functions, useful for the evaporation models.

Physical Constants

#define R_GAS 8.3144621 // Ideal gas constant [J/mol/K]

Clausius-Clapeyron

The function clapeyron() returns the thermodynamic equilibrium constant: P_{vap}(T)/P for a single chemical species.

clapeyron()

• Tint: interface temperature [K]
• Tboil: boiling temperature [K]
• dhev: Enthalpy of evaporation [J/kg]
• MWi: Molecular weight [kg/kmol]

double clapeyron (double Tint, double Tboil, double dhev, double MWi) {
  return exp (-dhev/R_GAS*MWi/1000. * (1./Tint - 1./Tboil));
}

Antoine

We define a function pointer for a generic antoine function. The pointer must be set by the user, to a specific antoine function depending on the chemical species under investigation.

#ifdef USE_ANTOINE

attribute {
  double (* antoine) (double, double);
}

#endif

For consistency, the temperature and pressure values provided to the antoine functions should be in SI units: K, Pa. Conversions necessary for the specific Antoine equation are manages inside each specific function. Each of the following functions return the thermodynamic equilibrium constant P_{vap}(T)/P using the Antoine equation, whose parameters were taken from the NIST database.

antoine_heptane(T,P): Antoine equation for n-heptane.

double antoine_heptane (double T, double P) {
  double A, B, C;
  if (T > 295)
    A = 4.02832, B = 1268.636, C = -56.199;
  else
    A = 4.81803, B = 1635.409, C = -27.338;
  return pow (10., A - B/(T + C)) / (P*1.e-5);
}

antoine_decane(T,P): Antoine equation for decane.

double antoine_decane (double T, double P) {
  double A, B, C;
  if (T > 367)
    A = 4.07857, B = 1501.268, C = -78.67;
  else
    A = 0.21021, B = 440.616, C = -156.896;
  return pow (10., A - B/(T + C)) / (P*1.e-5);
}

antoine_hexadecane(T,P): Antoine equation for dodecane.

double antoine_dodecane (double T, double P) {
  double A = 4.10549, B = 1625.928, C = -92.839;
  return pow (10., A - B/(T + C)) / (P*1.e-5);
}

antoine_hexadecane(T,P): Antoine equation for hexadecane.

double antoine_hexadecane (double T, double P) {
  double A = 4.17312, B = 1845.672, C = -117.054;
  return pow (10., A - B/(T + C)) / (P*1.e-5);
}