See the Verification section where results have been compared to analytical solutions.

xStream accurately models sonic choking at all three possible geometric conditions. See Sonic Choking for more information.

xStream’s solution methodology is based on the ideal gas equation modified with a compressibility factor. This compressibility factor can be obtained from an equation of state model or property library. The effect of the compressibility factor is carried through the fundamental equation derivations, and thus accounted for directly.

A junction has several advantages. First, solutions are given at all junctions, so the user can check the results at the junction. In contrast, Fittings & Losses are lumped into the pipe and it is not possible to give results at the loss. Second, many junctions (such as valves) have the ability to specify a CdA for sonic choking calculations. No such ability exists for Fittings & Losses; thus, sonic choking is always ignored for Fittings & Losses. Third, when using a junction the location in the pipe system of the pressure loss is specified. In other words, the upstream and downstream pipe lengths are specified. Since the location of the junction loss along a pipe can affect how much pressure is lost, the junction loss calculation is more accurate than the pipe fitting loss. A short explanation of this is that the pressure loss due to a K factor depends on the velocity squared. Typically, the velocity of the gas will change along the pipe, so the pressure drop of the K factor loss will depend on the local velocity. In the case of pipe fitting loss, it assumed to act like a friction factor and be evenly distributed along the pipe.

The pipe fitting approach has the advantage of being able to specify multiple losses quickly and easily, and not cluttering up the model Workspace with numerous junctions.

There is an overlap in capability between the Tank junction and an Assigned Pressure junction and frequently they are interchangeable. Here are the differences. The Tank junction input pressure and temperature always corresponds to stagnation properties. In the Assigned Pressure junction, they can correspond to either static (with one connecting pipe) or stagnation properties (with one or more pipes). The ability to represent static conditions is the reason the Assigned Pressure can connect only to one pipe when using the static option. Static conditions have a flow velocity associated with them and multiple pipes would have multiple velocities. If the stagnation option is used in the Assigned Pressure junction, it will behave identically to a Tank junction. Finally, the Tank junction can act as the reference pressure for a closed system, while the Assigned Pressure cannot.

Use the Resistance Curve Loss Model.

xStream supports the ANSI/ISA-75.01.01-2012 definition of valve Cv for gas flow. This can be modeled in valve junctions, relief valves, check valves, or control valves.

You must specify the "CdA for Choking" on the junction loss model tab. xStream uses this as the base area for sonic calculations. If modeling the subsonic loss as Cv, you can account for choking by specifying xT.