AFT Blog
AFT Fathom 8 has a new and improved method for predicting system pressures that involve laminar flow or non-Newtonian fluids. The Adjusted Turbulent K Factor (ATKF) method is used to apply corrections to pipes and components involving these special flows. The ATKF method can be enabled on the System Data tab in the System Properties window. Clicking on the question mark next to the ATKF method will access the AFT Fathom 8 Help Content that discusses the ATKF method in detail. In September 2012, Applied Flow Technology and DuPont published a technical article for the International Pump Users Symposium that discusses...
AFT Fathom 8 can be used to quickly and easily model multiple pump configurations with different pump speeds and impeller sizes. First, determine a particular pump curve to use from either a manufacturer’s pump curve or pump curve verification test data. Next, determine new pump curves for head and flow using the affinity laws considering either a change in pump speed or impeller size. The multiple pump curve data sets will then be entered for each particular pump configuration. In Figure 1 (click on the image to see it larger), there are a few pump configurations that have already been defined. ...
Relief valves can be modeled in four different configurations with AFT products and they are shown in the figure below. The required inputs for modeling a relief valve are the valve type, cracking pressure, valve loss model, and the exit pressure in the case of relieving to the atmosphere. There are three types of relief models available: Internal (Cases 1 & 1a), Relief Valve at Exit (Case 2), and Inline Exit (Case 3). In cases 1 and 1a, the relief valve is relieving into vent piping downstream of the valve. Note that there is initially no flow in the pipe downstream...
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...
Using “Specified Heat Rate In Constants” for the thermal model of heat exchangers can often cause problems in system models. The reason why is because this thermal model type causes the heat exchanger to act like an “assigned heat input” junction as does an assigned flow junction does for providing constant flow rates. Another problem is that this thermal model can cause unrealistic temperature changes across a heat exchanger. When the heat rate is specified and the mass flow rate and heat capacity are calculated based on the system solution, the temperature change will be whatever is required to maintain the...