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Calculating Results in Pipes and Junctions Not in Service

Posted in AFT Fathom, AFT Arrow, AFT Impulse

AFT flow modeling software allows you to easily change system line-up by closing junctions and pipes. How you take a portion of a system out of service affects what calculated results are available in output. Let's take the case where we have a valve, pipe, heat exchanger, pipe and valve in sequence.

To close one of the valves we can either open its specifications window, select the Optional tab and check 'Special Condition / Closed' or simply click the valve junction to select it then click the Special Condition button on the toolbar. A red "X" will appear next to the junction label and pipes with flow turned off will be displayed as a dashed line on the Workspace.`

If we close one of the two valves in the valve-pipe-heat exchanger-pipe-valve sequence, results in the Output window will show zero flow but pressures and, if we're doing heat transfer, temperatures, in all the pipes and junctions. Just as in a real system, closing only one valve will block flow but will still allow pressure and temperature to communicate to the pipes and components on either side of the closed valve.

Next let's close both valves in our valve-pipe-heat exchanger-pipe-valve sequence. As before the Output results will show zero flow but now 'No Solution' will be displayed for pressures and temperatures in the pipes and junctions between the two closed valves. Isolated on both sides, the pipes and junctions between the two closed valves cannot communicate to the rest of the system and, indeed, there is no information with which to calculate pressures and temperatures, hence the 'No Solution' display.

Now let's take the example of closing one of the pipes in the valve-pipe-heat exchanger-pipe-valve sequence. As with closing one valve output will show zero flow but pressure and temperature solutions will be available in all pipes and junctions. In real piping systems one doesn't close a pipe, of course, but AFT software provides this option as a modeling convenience so as not to force the inclusion of a valve junction just for the purpose of closing off part of a system.

Finally let's close two pipes and now we will see zero flow and, for the closed pipes and junctions between the closed pipes, 'No Solution' for pressures and temperatures. Closing two pipes is thus equivalent to closing valves at the far ends of the closed pipes.

© 2021 Applied Flow Technology