Hi there

Wondering if anyone can help me with a problem using ExternalMedia with the RefProp air thermofluid data.

I have a RefProp 9.1 licence, FluidProp and the ExternalMedia library. I've defined an air medium package using the ExternalMedia.Media.FluidPropMedium package in the usual way. I'm using Dymola as a front-end UI. Whenever I use the air medium, I get the following error:

"FluidProp error in FluidPropSolver::setFluidConstants:
Cannot compute saturation conditions at p = p_crit*(1 - 0.020480)"

The access to FluidProp and RefProp seems to work fine - I've not had any problems when trying the exact same process using a nitrogen medium model. My first thought is that ExternalMedia and FluidProp are trying to look up the air mixture data rather than the pseudo-pure fluid (.ppf) data in RefProp. I can't see any way to define this myself and assume since ExternalMedia doesn't yet handle mixtures that it would look up the .ppf data by default.

Has anyone come across this issue and can suggest a way to help me rectify?

As background, I'm basically trying to model an air liquefier and first experienced this problem when trying to model a Joule-Thomson valve. This is a pretty simple model and takes the incoming fluid pressure and specific enthalpy through a pressure drop. The process is assume isenthalpic, so the outgoing fluid properties are determined using the inlet enthalpy and the outlet pressure. I don't thing the fact that I'm trying to subcool this stuff is the issue - the model works fine with nitrogen or even using the CoolProp air medium. Also, I get the same error message if I use the air medium package in a simple flow model at room temperature.