Bend

The Bend junction type must always have two connecting pipes. This junction type allows you to model the irrecoverable loss that occurs when the flow direction changes through a bend or elbow. The Bend Properties window follows the first of the two basic Properties Window formats, displaying the connecting pipes in a fixed format. A flow direction through the junction is adopted from the defined directions of the two connecting pipes.

Standard Loss Types

The Bend Properties window offers several standard types of bend losses: the Smooth Bend, the Standard Elbow (the standard short radius threaded elbow), the Mitre Bend, and the User Specified K-factor. The window shows a schematic of the selected geometry for these three standard loss types. Until you have input the information for the upstream pipe that allows flow area determination, the standard Bend junction loss factor is not calculated. For smooth radius bends, you also need to specify r/D, which is the radius of curvature divided by the pipe diameter. At r/D values less than one, the Reynolds number must be known to calculate the loss factor, and therefore cannot be displayed until output is available.

For bends that are not at a 90-degree angle, you can select the radio button for Non-90 Degrees, enter the angle (0-180 deg), and the standard loss factor will be calculated.

Special Loss Types

The Bend also offers specialized loss types: the 3-K (Darby) method and Equivalent Length.

Additional Options

Basis Area for Loss Model - By default, the loss will be referenced to the upstream pipe area. This can be changed using the Basis Area for Loss Model dropdown.

Note: In principle, the upstream and downstream pipe diameters should be the same. However, the Bend junction only uses the reference area specified under Basis Area for Loss Model, even if the physical flow is in the opposite direction. If you are working with a user-specified loss, your geometry may have different diameter pipes connecting to the elbow. In this case, you would purposely define different upstream and downstream pipe areas. However, you would still want to be careful that the custom loss factor you assign is referenced to the correct area that is specified in Basis Area for Loss Model.

Restricted Flow Area - Optional input that is used only for checking if cavitation exists in the Bend junction.