I am trying to model combustion gas flow through a heat exchanger. The working fluid I am using is a mix of combustion products at ~2200K, one of which is water (superheated steam).
The pre-defined steam fluid is only defined up to 1250K, so using it limits my gas temperature to 1250K during the simulation. I have tried creating a user defined fluid, but I'm running into problems defining the coefficients of the ideal gas heat capacity polynomial - for some reason negative coefficients are not allowed. I have been trying to input coefficients based on a thermodynamics text on hand and the "NASA polynomials", but both contain negative coefficients.
Does anybody have any experience modeling high temperature water vapour or combustion products? If so, how did you successfully define the fluid?