The purpose of fluid groups is to allow heat transfer calculations in different loops which have different fluids. When enabled, a new menu item called Fluids appears on the Edit menu Groups flyout menu. Here is how this feature is enabled and used:

1. On the Fluid panel, select a base fluid

2. On the Heat Transfer/Variable Fluids panel, select Heat Transfer With Energy Balance (Multiple Fluids)

3. Select each pipe in the fluid loop on the Workspace and go to the Edit menu, Groups option, then Create to give the group a name. At this point the pipes and junctions are standard AFT Fathom groups.

4. Go to the Heat Transfer/Variable Fluids panel

5. Check the Use As Fluid Group box for the desired fluid group

6. Specify what fluid is to be used in each fluid group.

7. Click OK

Now when you run the model, each of the pipes and junctions in each group will take on the fluid properties assigned to that fluid group.

Note: If you are using a custom fluid in your model and make changes to it in the fluid library, you will need to save and re-open the model for the changes to be applied to any fluid in a Fluid Group.

Here are some guidelines for use:

• A pipe or junction can belong to one and only one fluid group

• Every pipe and junction must belong to a fluid group

Use with Heat Exchangers

Fluid groups allow heat exchangers to be modeled with thermal links to other heat exchangers carrying different fluids.

Thermal Links

When modeling convective heat exchangers (such as parallel or counterflow) two heat exchanger junctions can be linked thermally. A thermal link is when two heat exchanger junctions, which are hydraulically isolated, can exchange heat with each other. Typical use is when the two heat exchangers represent two sides of the same physical heat exchanger. When thermal linking specified in a heat exchanger properties window, the user must specify the heat transfer area and overall convection coefficient. AFT Fathom will force the two heat exchanger junctions to use the same value.