Screen
The Screen junction type requires two connecting pipes. This junction type allows you to model the irrecoverable loss that occurs through a screen, mesh, or filter flow restriction. It also allows you to specify loss factors as a function of a flow parameter.
The Screen Properties window follows the first of the two basic Properties window formats, displaying the connecting pipes in a fixed format. The Screen junction does not have an explicit flow direction; it adopts a flow direction from the connecting pipes.
AFT xStream provides four standard screen types for your use: sharp-edged perforated plate, round-edged perforated plate, circular wire screen, and silk thread screen. The loss factors for these screens are taken from handbook values. In addition to the standard screens that AFT xStream provides, you may enter your own custom screen loss factor that is consistent with the application.
When you select Resistance Curve, the Screen Properties window makes additional features available. Using these new features you can input Screen loss factors or pressure drops that vary with flow. To enter these factors, you can fit a curve to available data, or use interpolated x-y data. You can choose any of the optional flow and pressure parameters provided; you can also specify the most convenient units.
When a variable loss is specified, AFT xStream modifies the loss factor in the Solver to agree with the solution. You can choose any of the optional flow and pressure parameters provided, and you can specify the most convenient units.
CdA for Sonic Choking
An optional input in the Screen Properties window is the CdA. This parameter describes the effective area restriction in the screen for the purpose of calculating sonic choking. In most cases, information on the CdA must be obtained from the vendor or test data.
