Note: The Volume Balance junction must be used with great caution. It is only intended to model specific situations and when used incorrectly will give incorrect results. When modeling mixing fluids with varying fluid properties, the Output will likely show a Caution message about the density change. This does not necessarily mean that a Volume Balance should be used at the mentioned location.

The Volume Balance junction type is internal to the system and requires two connecting pipes.

The Volume Balance Properties window follows the first of the two basic Properties window formats, displaying the connecting pipes in a fixed format. The flow direction through the junction is determined by the defined directions of the connecting pipes.

The Volume Balance junction is useful for modeling pipelines with a moving interface between fluids of different density. Such a scenario is in reality a transient application, because the mass in the system is not steady with time. Impulse is designed to balance mass at all branches, except for the Volume Balance junction. For the Volume Balance, the volume is balanced between the upstream and downstream pipes. This is consistent with the fact that an equal velocity exists at the interface, resulting in a volume balance at the interface. AFT Impulse assumes the interface does not move during the transient.

Volume Balance junctions should be used in conjunction with the variable fluid properties model (see Variable Fluids panel).

The usage of a Volume Balance junction is illustrated with the example below.  Figure 1 below provides a summary of the four snapshots in time that occur in the example. In reality, injecting slurry into a pipeline where there are two separate fluids with an interface between is a transient situation with a moving interface. In Impulse, this junction can be used to represent an interface which does not move rapidly in the transient. There is no option to define transient data for this junction.