Helium Transfer - ANS (Metric Units)

Summary

This example will show how to use the ANS module to size a system based on pipe weight to deliver a minimum flow of helium for variable inlet temperature.

Note: This example can only be run if you have a license for the ANS module.

Topics Covered

• Sizing using pipe weight

• Creating Common Size Groups

• Using dependent design cases to satisfy two different operating modes for a system

Required Knowledge

This example assumes the user has already worked through the Beginner: Air Heating System example, or has a level of knowledge consistent with that topic.  You can also watch the AFT Arrow Quick Start Video (English Units) on the AFT website, as it covers the majority of the topics discussed in the Beginner: Air Heating System example.

In addition, it is assumed that the user has worked through the Beginner: Three Tank Steam System - ANS example, and is familiar with the basics of ANS analysis.

Model Files

This example uses the following files, which are installed in the Examples folder as part of the AFT Arrow installation:

• US - Helium Transfer - ANS Initial.aro

• US - Helium Transfer - ANS Final.aro

Step 1. Start AFT Arrow

From the Start Menu choose the AFT Arrow 9 folder and select AFT Arrow 9.

To ensure that your results are the same as those presented in this documentation, this example should be run using all default AFT Arrow settings, unless you are specifically instructed to do otherwise.

Open the US - Helium Transfer - ANS Initial.aro example file listed above, which is located in the Examples folder in the AFT Arrow application folder. Save the file to a different folder. The Workspace should look like Figure 1 below.

In this system, Helium flows from one tank to two other delivery tanks. Throughout the year its inlet temperature varies from 32 to 100 deg. F. There is a minimum flowrate required to each tank of 2.5 lbm/sec. Since the supply temperature can vary we will analyze two different design cases, one for the maximum temperature (Hot Case), and one for the minimum temperature (Cold Case). We are using the Hot Case as our primary design, so the model inputs currently reflect the Hot Case. We will need to first define the sizing settings for the primary case, then set up the secondary case using the cold temperatures.

Step 2. Define the Modules Group

Navigate to the Modules panel in Analysis Setup. Check the box next to Activate ANS. The Network option should automatically be selected, making ANS enabled for use.

Step 3. Define the Automatic Sizing Group

To define the Automatic Sizing group, go to the Sizing window by clicking on the Sizing tab.

A. Sizing Objective

Go to the Sizing window by selecting the Sizing tab. The Sizing Objective window should be selected by default from the Sizing Navigation panel along the bottom. For this analysis, we are interested in sizing the system considering the monetary cost for the initial costs only.

1. Select Perform Sizing for this calculation.

2. For the Objective, choose Pipe Weight, and select the Minimize option from the drop-down list if it is not already selected.

The Sizing Objective window should now appear as shown in Figure 2.

B. Sizing Assignments

On the Sizing Navigation panel select the Sizing Assignments button.

For this system we will be sizing all of the pipes since it is a new system.

ØMove each of the pipes to Always Include in Weight.

The piping to each of the discharge tanks in the system will be identical, so a Common Size Group will need to be created to link the sizes in the two pipes.

Above the Pipe Grouping table select New, then give the group the name Discharge Pipes. Select the radio buttons to place pipes P2 and P3 in the Common Size Group.

The completed pipe Sizing Assignments can be seen in Figure 3.

C. Candidate Sets

Click on the Candidate Sets button to open the Candidate Sets panel.

For this system it is desired to use STD Steel - ANSI. To create a Candidate Set, do the following:

1. Under Define Candidate Sets, click New.

2. Give the set the name STD Pipes and click OK.

3. From the drop down list choose Steel - ANSI.

4. In the Available Material Sizes and Types on the left, expand the STD pipe sizes list.

5. Double-click each of the sizes from 1 to 10 inches to add them to the list on the right.

6. In the Select Pipe Sizes window, click OK.

We now need to define which pipes will use this Candidate Set during the sizing calculation. Select the radio buttons next to pipe P1 and the Common Size Group to assign the Candidate Set to each of the pipes, as shown in Figure 4.

D. Design Requirements

Select the Design Requirements button from the Navigation Panel.

For this system there is only one Design Requirement, which is the requirement to maintain a minimum flow of 2.5 lbm/sec into each of the discharge tanks. To define this requirement:

1. Click New under Define Pipe Design Requirements.

2. Enter the name Minimum Flow.

3. Select Mass Flow Rate as the Parameter.

4. Choose Minimum for Max/Min, and enter 2.5 lbm/sec.

Now we need to apply the defined Design Requirement to the discharge pipes.

ØCheck the box next to Discharge Pipes in the Assign Design Requirements to Pipes section. The Design Requirements panel should now appear as shown in Figure 5.

E. Assign Cost Libraries

When the Sizing Objective has been defined as monetary cost, it is necessary to create and assign cost libraries for the automated sizing, which can be done in the Assign Cost Libraries panel. Since we have defined the objective as Pipe Weight, we will not need to assign any cost libraries, and this button is disabled.

F. Sizing Method

Select the Sizing Method button to go to the Sizing Method panel.

Ø Choose Discrete Sizing, if not already selected since it is desired to select discrete sizes for each of the pipes in the model.

This model is relatively simple, so the default, Modified Method of Feasible Directions (MMFD), should be sufficient. Ensure that this method is selected from the list of Search Methods.

G. Dependent Design Cases

We have now set up the system to be sized for the primary design case, but we will also need to account for the cold case where the system is operating at the minimum inlet temperature. To do this we will create a dependent design case by completing the following steps:

1. Go to the Sizing Objective panel and select the Enable Dependent Design Cases option. A new button will now be available for the Dependent Design Cases panel in the Sizing Navigation panel.

2. Navigate to the Dependent Design Case panel. You should now see instructions displayed to create Dependent Design Cases, along with a summary table of dependent design settings. We will now need to use the Duplicate Special feature to create the dependent design cases.

3. Go to the Workspace and choose Select All from the Edit menu.

4. Open Duplicate Special (from the Edit menu), enter an increment of 10 and select Make Dependent Design Case (Figure 6). Click OK.

5. Move the duplicated pipes and junctions to distinguish them from the original ones from the Primary Design Case. The Workspace should now appear as shown in Figure 7.

6. In the Cold Case inlet tank J11, open the Tank Properties window and change the temperature to 32 deg. F.

Return to the Dependent Design Cases panel.

When Duplicate Special was performed with Dependent Design Case selected, each of the duplicated pipes was created with a special type of grouping. For example, pipe P11 is grouped with pipe P1 as a DDC pipe (see Figure 8). This type of assignment allows the dependent design pipes to be sized, but to not be counted in the cost so that the cost will not be duplicated.

It should also be noted that the dependent design grouping causes each of the dependent pipes to inherit their Common Size Groups, Candidate Sets, and Cost Library settings (if applicable) from the pipes in the primary case. The dependent design case pipes are therefore hidden on all sizing panels except for the Design Requirements and Dependent Design Cases panels.

Step 4. Run the Model

Click Run Model on the toolbar or from the Analysis menu. This will open the Solution Progress window. This window allows you to watch as the AFT Arrow solver converges on the answer. Once the solver has converged, view the results by clicking the Output button at the bottom of the Solution Progress window.

Step 5. Examine the Output

After the run finishes, examine the final pipe sizes calculated by the ANS module. The results for pipe size and overall cost are shown in Figure 9. It can be seen that the 5 inch and 3 inch pipe sizes were chosen for the header and discharge pipes, respectively. The overall weight of the system is 22,194 lbm.

Conclusion

By creating a dependent design case both the hot and cold temperature operating cases were able to be taken into account in the automated sizing for this simple system. In more complex systems additional dependent cases could be created to consider various system configurations as well as further operating conditions.