Class 3 Error
SYMPTOM:
A case using the Redlich Kwong equation of state may have inaccuracies in phase change predictions, and give differents results to Release 10.0.
PROBLEM:
Various liquid phase saturation properties are being set to values predicted by the raw Redlich Kwong equation of state instead using the more accurate equations or correlations listed in the documentation. The list of inaccurate properties is:
- density (should use the Rackett equation)
- enthalpy (should be offset from the gas value by the latent heat correlation mentioned in the documentation)
- specific heat capacity at constant pressure (should use the the Cp correlation presented in the documentation)
- specific heat capacity at constant volume (should use the Cp correlation presented in the documentation)
- entropy (should be offset from the gas value by -(latent heat)/Tsat(p))
The inaccurate predictions of the raw Redlich Kwong equation of state for liquid phase properties will mainly lead to inaccuracies in phase change predictions when running the equilibrium wetness model (equilibrium phase change) or the thermal phase change model (non-equilibrium
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WORKAROUND: For steam calculations, a workaround is to use the IAPWS equation of state instead. There is no workaroundcurrently available for other materials. FIXED IN: ANSYS CFX Release 11.0 Update 1. |
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