The Spray Discharge junction must have at least one connecting pipe, and it allows up to four. This junction offers a flexible way of modeling a flow exiting the system through a nozzle or spray device.
The Spray Discharge Properties window follows the second of the two basic Properties window formats. A table displays the connecting pipe information. The pipe table grows in size to accommodate up to four connecting pipes.
The exit pressure to which the Spray Discharge junction discharges must be entered, as well as the temperature in case of inflow.
Two geometries can be modeled. The first is a normal, one hole spray, where the discharge flow area of the hole is entered. The second is a sparger which, in principle, works in the same way as a spray. For the sparger, the flow area of a single hole and the number of holes are entered. This assumes that the holes are hydraulically close in proximity and are the same area.
For each connecting pipe, the pipe table on the Pipe Losses tab lists the reference flow direction and up to two loss factors. The first loss factor is for physical flow out of the pipe and into the junction, the second is for physical flow into the pipe and out of the junction. The loss factors can be specified independently or left as zero. To edit within the pipe table, click in the appropriate column and row.
The discharge coefficient for the junction is entered in the appropriate box. The physical area of the exit flow can also be entered. These two parameters are used to calculate the discharge flow rate, which depends on the difference between the internal pressure in the system and the specified exit pressure.
If you select a Resistance Curve, the Spray Discharge Properties window makes additional features available. Using these new features you can input the spray pressure drop that varies with flow. To enter these factors, you can specify polynomial constants, fit a curve to available data, or use interpolated x-y data.
When a variable loss is specified, AFT Arrow 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 Spray Discharge Properties window is the CdA. This parameter describes the effective area restriction in the spray for the purpose of calculating sonic choking.
Note: The CdA for sonic choking may be different from the subsonic CdA loss model option in Arrow. The discharge coefficient can vary at different pressure ratios due to the vena contracta moving closer to or farther from the orifice restriction. For the highest accuracy the CdA used for subsonic and sonic losses should be tested and entered separately. See the "Modeling Choked Flow Through an Orifice" white paper on AFT's website for more information.
The Special Condition for a spray discharge always closes it.