Learning Forum

[Shamkhal Mammadov]

I am trying to simulate CO2 flow through a pipe with a diameter decrease (valve). I have Pressure inlet(1000 psi) and pressure outlet (200 psi) boundary conditions.  Co2 density given via real-ga peng Robinson. 

Energy is on;

Single phase;

viscous model - k-epsilon, enhanced wall treatment.

However, when I lower the input pressure my model works fine:

 

(on the figure I have a scenario when my inlet set to 300 psi and my Outlet set to 200). It works fine and I can see the temperature change.

 

[Shamkhal Mammadov]

I am trying to study Joule–Thomson effect.

[Rob]

Is the model diverging? Are you wanting to see the jet evolve or the steady result? 1000psi is about 70bar, so you're likely to see shocks. Are you anywhere near the conditions for liquid CO2?  100psi is around 7bar so you may not be supersonic: I've not done the maths to check. 

[Shamkhal Mammadov]

Hello there, thank you for the reply.  I usually set the inlet and outlet to 200 psi. then I set the total gauge pressure to 1000 psi, I set up animations for velocity, pressure, and temperature. then I observe results through animations.

it works fine with pressures up to 350. when I increase the pressure more, it crashes (residuals blow up.).

what could be the problem? the whole purpose is to watch how the temperature in an area with a small diameter change as inlet pressure increases.

[Rob]

Is the inlet pressure increasing with time, or you're comparing several steady runs with different inlet conditions? 

Have a look at the flow field in the nozzle, post a zoomed in plot of Mach Number. As you move from 200psi to 350psi would you expect the flow to become supersonic?