Area Change
The Area Change junction type requires two connecting pipes. This junction models the irrecoverable loss that occurs at the area transition between two pipes, whether expansion or contraction.
The Area Change Properties window follows the first of the two basic properties window formats and displays the connecting pipes in a fixed layout. The flow direction through the junction is determined from the defined directions of the two connecting pipes.
The Area Change Properties window provides two standard area-change loss types: Conical Transition and Abrupt Transition.
The key parameter that influences the magnitude of the area-change loss is the area ratio between upstream and downstream pipes. The standard Area Change junction loss factor is not calculated until the upstream and downstream pipe data required to determine flow area is defined. For conical transition geometries, the conical angle must also be specified. This angle ranges from 0 to 180 degrees, where 0 degrees represents a transition over an infinitely long length and 180 degrees represents an abrupt transition.
If the standard loss factors provided are inadequate for the application, a custom loss factor can be specified based on an area defined for the junction.
Note: A vena contracta can occur through a physical area change. At sufficiently high velocities, the Mach number may reach sonic conditions and the flow may choke. The optional CdA input parameter represents this vena contracta and corresponds to the minimum possible sonic-flow area. When this area is entered as CdA and sonic conditions are reached, xStream solves the system on a choked flow basis.
