# AFT Blog

Welcome to the Applied Flow Technology Blog where you will find the latest news and training on how to use AFT Fathom, AFT Arrow, AFT Impulse, AFT xStream and other AFT software products.

## Modeling the Stack Effect in AFT Arrow

AFT Arrow solves all of the fundamental controlling equations governing gas dynamics. For more information about which fundamental thermodynamic equations are solved in AFT Arrow, here is an excellent article that discusses gas flow calculations in detail.   The "stack effect" is simply one aspect of these equations, and is accounted for by the user input and boundary conditions. Ultimately, flow is driven by pressure difference. The higher you raise a chimney, the lower the atmospheric density and pressure at the discharge. In order to accurately model the "stack effect", the system boundary conditions must be modeled accurately.  As the discharge...

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## What About Viscosity Corrections?

Previously, I wrote an article that discussed how to account for density differences between a pump manufacturer's test fluid and a system fluid for pumps as well as the importance, https://www.aft.com/blog/entry/2014/12/02/reference-densities-for-pump-operation.  Both AFT Fathom and AFT Impulse can take into account these density differences very easily, thus, reducing the efforts for the user. But what about viscosity corrections?  Is it important to take this into account as well?  How is this accomplished?  Does it really make a difference? If the system fluid you are modeling has a HIGHER VISCOSITY (more resistant to flow) than the fluid the pump was tested with,...

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## Reference Densities for Pump Operation

You have just received a pump curve from a manufacturer to use in modeling your piping system.  However, the pump manufacturer only tested their pump with water while your system fluid has a density that is different than water.  These differences need to be accounted for with your flow model as well.  This may sound like a bit of a daunting task up front. But there is good news!  In AFT Fathom 8 and AFT Impulse 5, there are two very helpful features that will allow you to easily account for these differences with no trouble at all! The pressure rise...

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## Viewing Output Across Multiple Scenarios

AFT Arrow 4.0 and AFT Fathom 7.0 offer the ability to view text output across multiple scenarios simultaneously, greatly facilitating seeing the differences in results between scenarios. To view multiple scenario output, open Output Control either from the Analysis menu or, when the Output window is active, by clicking the toolbar button, and then selecting the Multi-Scenario tab. Under Display Type select Selected Scenarios and click the Select Scenarios button to open the Select Scenarios window. Select the scenarios you want to see output for and click OK to return to Output Control where the selected scenarios will now appear in...

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## Using Groups

Groups of pipes and junction can be named for later recall. This is done using the Group Tools on the Edit menu. Groups may have subgroups, and pipes and junctions may be members of multiple groups. To create a group select the pipes and junctions you want in the group, then select Edit/Groups...Create. Specify a name for the group, click OK and the Group Manager will be displayed showing the pipes and junctions in the group. Group Manager can also be used to add or remove pipes and junctions from an existing group, rename a group or delete a group. After...

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## Making Use of the Quick Access Panel

With the release of AFT Fathom 8 and AFT Impulse 5, there is an incredibly useful new feature available on the Workspace called the "Quick Access Panel".  This feature allows you to quickly and easily work with several useful features of the software in one area such as the Scenario Manager, Pipe and Junction Inspection, Workspace Overview Map, the Checklist, and ability to activate the add-on modules. Scenario Manager Access to the full Scenario Manager capabilities exists in the Quick Access Panel.  Add new scenarios, clone scenarios, promote scenarios, re-order scenarios, add notes for scenarios, etc. Properties The Properties tab in...

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## Estimating Pump Inertia, Specific Speed, and Four Quadrant Data within AFT Impulse 5

An excellent new feature of AFT Impulse 5 is that it is possible to estimate the pump inertia, specific speed, and four quadrant data sets directly within AFT Impulse 5!  No more need to perform external spreadsheet calculations for these estimates. In addition to that, AFT Impulse 5 can use the entered pump and power/efficiency curve to perform these estimates which makes things much easier and efficient!! First step is to enter pump curve data and generate the curve fits as shown in Figure 1. Figure 1:  Pump Performance Curve from Entered Data   Next, click on the "Transient" tab of...

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