IdealGasMixtureFluidProperties

This is a VaporMixtureFluidProperties where each of the components are assumed to be ideal gases, such as IdealGasFluidProperties or NASA7IdealGasFluidProperties. A fluid properties class can be a component if it implements IdealGasMixtureInterface, which tells the mixture whether its specific heats are constant and at which temperature Newton's method should start.

First note the following definitions and relations:

where

• is the mass of component ,

• is the mixture mass,

• is the number of moles of component ,

• is the mixture number of moles,

• is the molar mass of component , and

• is the mixture molar mass.

Due to Dalton's law of partial pressures,

where is the partial pressure of component and is the mixture pressure.

Mixture mass-specific properties, such as specific volume and specific internal energy are computed as mass-fraction-weighted sums of the component properties evaluated at the mixture temperature and pressure:

Mixture entropy is an exception to this rule, as the component entropies must be evaluated at their partial pressures, rather than the mixture pressure, in accordance with the Gibbs' theorem, which accounts for the entropy of mixing (Çengel and Boles, 2008):

The temperature is computed from the specific volume and the specific internal energy by solving

for ; the internal energy of an ideal gas does not depend on pressure. When all components have constant specific heats, the internal energy is linear in temperature and follows explicitly. Otherwise, is found with the 1D Newton solver of the fluid properties utilities, starting at the lowest of the start temperatures of the components whose specific heats are not constant. For NASA 7-coefficient components, these are the upper ends of the temperature ranges of their data, above the solution, for the reasons given in NASA7IdealGasFluidProperties. The equation is offset by a constant that makes both of its sides close to , where is the mixture isochoric specific heat, so that the convergence test of the solver bounds the relative error in temperature even where the internal energy is close to zero. The pressure then follows from the ideal gas law, , where is the universal gas constant.

Transport properties such as dynamic viscosity and thermal conductivity are computed as molar-fraction-weighted sums of the component properties evaluated at the mixture temperature and pressure:

NASA7IdealGasFluidProperties does not yet provide viscosity or thermal conductivity, so these properties are not yet available for mixtures with its components, and neither are flow models that need them, such as the gas-mixture flow channels of the thermal hydraulics module.