AFT Blog
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...
A new feature in AFT Fathom 7.0, orthogonal pipe drawing automatically inserts an intermediate vertex into a pipe and adjusts the length of the pipe segments to create a right angle graphical bend between the pipe end points. Orthogonal drawing can be turned on either from Options, Workspace Preferences Display Options tab, or quickly toggled on and off with the F4 key. By toggling orthogonal drawing on and off you can easily mix pipe drawing modes and even have drawing modes compliment each other. For example, with orthogonal drawing toggled off, select a pipe and insert a segment using AFT Fathom's...
The zoom select tool is a quick way to zoom into an area of interest. If you click the zoom select tool and draw your selection box the selected area will expand to fit the selection box. The drawn selection box will expand to fit your Workspace so that the magnification will will vary according to the size of the selection box and the area of the model selected. Alternatively you can always have zoom select zoom to 100% by clicking the zoom select tool then holding the shift key down while you draw the selection box and release the mouse...
You probably already know that you can quickly view a summary of the input data for any object in your model with the Inspection Window. Simply place the cursor over a pipe or junction and 'right click' your mouse ('left click' for you lefties). Think how handy it would be if you could also see a summary of output information on the Workspace. You can and it's as easily done as viewing the Inspection Window by holding the 'ctl' key down as you right click. P.S. - In case you didn't already know, holding the 'shift' key down while right clicking...
Under sub-sonic gas flow conditions, loss models can use the familiar K, Cv or resistance curve methods. At choked flow, however, the dynamics of compressible flow require a different method to characterize the loss, which AFT Arrow users will see as the optional 'CdA' input value on the valve and other junctions specifications window. The product of coefficient of discharge and effective flow area under choked conditions, AFT Arrow can directly calculate the CdA for some cases, such as at the discharge from a pipe. For other components, such as valves, determining these values is most commonly done through flow testing....
If you are using multiple fluids in the same Excel Add-In worksheet, you display which fluid or fluid alias is used in an Excel cell by using the "Fluid" or "FluidAlias" function.
We're not talking about literally adjusting atmospheric pressure here, rather, the ambient reference pressure used in AFT software. The default value is 1 standard atmosphere, but can be changed as desired. Open System Properties either from the Analysis menu or by double clicking the System Properties check box in the status bar, and select the System Data tab. Enter the desired value in the 'Atmospheric Pressure' field and select the appropriate pressure unit in the adjacent unit drop down box. Gauge pressures, NPSHA and cavitation calculations will reflect this specified atmospheric pressure. Note that this does not change the value of...