Helium relief line - 'clip pressure for properties'
I'm modelling the flow of cryogenic helium across a heat exchanger (a coil inside an annulus). The assumed boundary conditions are approx sonic flow in and 1 bar out; this represents a volume of liquid helium abruptly vapourising and flowing through a relief valve to atmosphere. I'm looking for a max pressure.
I have the helium set as an ideal gas which is probably not entirely correct but it's closer than having it as incompressible like I had before... I'm only really looking for a ballpark figure in any case. I got an error saying that the absolute pressure is out of range, or something along those lines. A bit of reading suggested that my reference pressure was incorrect and resulting in a negative absolute pressure, so I turned on the 'clip pressure for properties' in solver control. It appeared to work, although the solution converged after a worryingly short period of time (only 10 or so iterations). Even though the results in post seem to be reasonable, I don't really understand what I've just done, why it's worked and what the original problem was...so I don't trust the results at all!
Any advice/help much appreciated.
If you are getting negative absolute pressures it is more likely than not that your setup is wrong and fudges like clipping the pressure is just covering up a major flaw.
Check your material model and boundary conditions. They are almost certainly not physically possible.
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