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How can I change the vapor pressure limit based on fluid properties, for fluids other than water? How does this affect the transient simulation results?
The default of -1 bar is for water at 20 C. If you're using a fluid other than water, the vapor pressure limit can be changed according to the values in the Liquid Engineering Library. To do this, click on the Vapor Pressure field in the properties of the Transient calculation options, then click the ellipsis button (...) next to it. Expand the liquid library, select the appropriate liquid, then click the Select button. You will notice that the Vapor Pressure field will change accordingly.As for how this affects the transient simulation: when the pressure at any given point in the network drops below the vapor pressure limit set in the calculation options, a vapor pocket will form. So, if subatmospheric pressures are occurring in your system, selecting the right vapor pressure limit may be important for an accurate simulation.
For example, if your pressure drops to -1.01 bar and your liquid has a vapor pressure limit of -1.1 bar, then you will see a vapor pocket form with the default vapor pressure (-1.0), but will not see one form with your liquid's vapor pressure limit. This can certainly affect the minimum and maximum transient pressures, because vapor pockets can cause severe upsurge pressures when they collapse.If you need to add a new liquid to the Liquid library, go to Components > Engineering Libraries, expand Liquid Libraries, right click LiquidLibrary.xml, choose "add item" and fill in the fields. This will now be available to choose from. You can also edit the vapor pressure values of existing liquid library entries if needed.Of course, you always have the option of simply manually entering the appropriate vapor pressure limit, but you should also select the liquid in the Steady State/EPS Solver calculation options, so that the Initial Conditions are calculated correctly according to that liquid.
Modeling fluids other than water