I am trying to simulate carbon dioxide discharging from the pipe using ansys fluent and want pressure variation with time inside the pipe. The geometry consists 144m long pipe and 146.36mm inner diameter. I created axisymmetric geometry with environment at the exit of pipe. The wall of the pipe defined as adiabatic while the environment external to pipe defined as pressure outlet with 1am and 290.5K and inside condition to pipe is patched to 38.1 barg and 278.1K.

Axisymmetric, transient, Pressure based solver

Laminar, Energy eqn. ON

BC: same as described above

Pipe fluid material: co2 (Not co2-) [ PR EOS for density, (cp, viscosity, thermal conductivity)=default constant] (Kept things constant because of simplicity)

Environment fluid material: Air [PR EOS for Density , other things const]

SIMPLE algorithm, (density, energy, temperature)=first order scheme, Pressure=standard

Time step=0.001 second, iteration per time step=200 (resiuduals are not converging...continuity goes up to 100 and stays constant)

Paper I am referring is: "PREDICTING THE DECOMPRESSION CHARACTERISTICS OF CARBON DIOXIDE USING COMPUTATIONAL FLUID DYNAMICS" in which it is mentioned as test no 3. The similar setup I created for 258m long pipe but the results are same over there as well.

I tried with NIST real gas model but the temperature and pressure goes outside the range of the table so it shows error.