How does Fluent calculate the specific enthalpy for incomp. ideal gas?
 

Dear Users,

I am currently doing a CFD simulation in Ansys and was trying to grasp the energy equation that Fluent solves. In the Theory Guide 15.0, chapter 5.2.1.1., it is stated that for ideal gas, the specific enthalpy of a mixture is calculated through equation 5.3, whereas with an incompressible flow, it is calculated through equation 5.4.

What equation does Fluent use when the density of a mixture is calculated through incompressible ideal gas? I understand that if this density calculation option is checked, then the flow is treated as incompressible through pressure changes. Does this mean that equation 5.4 is used, as Fluent treats the flow as incompressible?

Also, if someone knows - why do the equations differ (5.3&5.4) in the way that they do? Is there some derivation which I can look up?

Thanks for the help and sorry if this has already been asked before, I genuinely tried looking this up to no avail.