AFT Blog

Many times when modeling heat transfer using heat exchangers in AFT Fathom, significant temperature differences across the heat exchanger can have a major impact on the accuracy of the heat transfer results.  This can especially become a problem with non-linear heat capacity relationships.  The heat transfer across the heat exchanger in the model below is calculated from the temperature difference across the heat exchanger and the arithmetic average heat capacity. One way to enhance the accuracy of the heat transfer results is to model the single heat exchanger junction, J2, as multiple heat exchangers as shown in the below model. The...

AFT Arrow can be used to model various types of choking such as restriction choking, endpoint choking, and expansion choking. A useful parameter in AFT Arrow’s output is the “Sonic Flow Area” and this is the flow area in which sonic choking will occur. Comparing the sonic flow area to the actual flow area can help determine the margin between not choking and choking. The figure below provides a conceptual understanding of comparing various sonic areas to the actual flow area of a compressible system. If one defines their system such that the sonic area (ASonic,1) is less than the flow...

AFT Arrow can be used to model various types of choking such as restriction choking, endpoint choking, and expansion choking.  A useful parameter in AFT Arrow’s output is the “Sonic Flow Area” and this is the flow area in which sonic choking will occur.  Comparing the sonic flow area to the actual flow area can help determine the margin between not choking and choking. The figure below provides a conceptual understanding of comparing various sonic areas to the actual flow area of a compressible system.  If one defines their system such that the sonic area (ASonic,1) is less than the flow...

All of the pipe numbers in Fathom must be unique. When adding a pipe to a model, the new pipe number will be incremented based on the highest pipe number currently in the model. For example, you may only have 25 pipes on the workspace, but if the highest pipe number is 100, a new pipe will automatically be assigned number 101. After several iterations of deleting and adding new pipes, the numbering scheme may be reduced to chaos. AFT Fathom provides three tools to quickly and easily renumber pipes. They can be found in the Edit menu.   The Renumbering...

Viewing the output from multiple scenarios in the same window can be a valuable and time saving tool! You must have output available for each of the scenarios you would like review. One way to do this is by executing a batch run: Select “Start Batch Run…” from the file menu.Click “Add Scenarios” and select which scenarios you would like to include in your multi-scenario output.Click “Start Run” and sit back while each of the scenarios is run. In order to view output from multiple scenarios in the same window, follow these steps: Browse to the Output window of one of...

Filters and screens impose a pressure drop that varies with flow rate. The variation is non-linear, but manufacturers will often provide only one data point for pressure loss at the design flow rate. Using a single point, or constant pressure drop, can produce significant inaccuracies in your model. With this in mind, AFT offers the “Fill As Quadratic” option for entering loss data. Using only a single point, “Fill As Quadratic” will create two additional points for you. This first is simply 0,0; zero flow produces zero pressure drop. The second point is 2 x Flow and 4 x Pressure Drop....

You can jump from junction to junction or from pipe to pipe by pressing F5 while in a specifications window.