In the picture you can see the subsystem that contains the Receiver Accumulator involved with this problem. The Accumulator is connected to a thermal network of course. At some point in the simulation, Liquid Helium is able to fill the container without evaporating. When the filling level reaches a little more than 50%, the simulation stops along with the error message "Specific internal energy of liquid volume must be greater than or equal to Minimum valid specific internal energy."
However, the set mininum specific internal energy is negative (-6.3 kJ/kg).
So what is the (general) reason for this error? How can the specific internal energy become negative? What modifications could I make to the Receiver Accumulator to fix the problem?
A few FYI's:
1) Shortly before the error occurs, the specific internal energy of the gaseous helium shows strong oscillations.
2) The higher the helium flow into the accumulator, the earlier this error occurs.
3) You can ignore all black parts