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AFT Product Tips

Welcome to the Applied Flow Technology Blog where you will find the latest news and training on how to use AFT Fathom, AFT Arrow, AFT IMpulse, AFT xStream and other AFT software products.
Erin Onat

Are you for real? Understanding and Troubleshooting Artificial Transients in AFT Impulse

I tend to reflect on the truly endless list of things I am so grateful for. While this list is by no means exhaustive, some of these things include my loved ones, my awesome job at AFT, the bounty of pumpkin-flavored treats that sweeten up my fall-time snacking options, and of course, AFT Impulse’s detection of artificial transients. While the dreaded Warning message that an artificial transient triggers can cause any engineer’s stomach to turn, I’ll explain why every AFT Impulse user should add this feature to his/her list of things to be thankful for as well. Let’s start with an...
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Recent Comments
alen
Thank you Erin for drawing our attention to this issue. One thing that I miss here is HOW to resolve the issue. How to specificall... Read More
Tuesday, 14 November 2017 09:52
Erin Onat
Thank you for taking the time to read my blog and to give me some feedback! The model discussed in this blog involves a somewhat... Read More
Friday, 01 December 2017 01:40
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Applied Flow Technology

Using Branch Junctions to Model Desuperheaters

Superheated steam is often used in mechanical power applications, such as driving turbines. For heating or industrial processes, however, saturated steam is more efficient. Desuperheaters are used to lower the temperature of superheated steam, so that it can be more effectively used in industrial processes. A desuperheater lowers the temperature of the steam by injecting water. Now, the question is, how can you model a desuperheater within AFT Arrow? AFT Arrow is a single-phase program for compressible flow, so it cannot model liquid water. Conveniently though, there is a feature built into the branch junction that can model a desuperheater. You may...
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Erin Onat

Closing the Loop on Modeling Closed Loop Systems in AFT software

For several users of AFT software, it goes pretty predictably: first you place a pressure junction, then maybe a pump, then some sources of pressure drop including valves and heat exchangers, and then the model is finished off with another pressure junction. Of course, this is greatly oversimplifying the process and the vast array of systems that are modeled with AFT software, but here’s my point: most users are more familiar with modeling open systems that include individual pressure junctions located both upstream and downstream of the system. But what about modeling closed systems? The truth is that modeling closed systems...
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Recent Comments
Kevin
Really nice article! This greatly simplifies the thought process around closed systems. I think it's worth noting that the absol... Read More
Monday, 18 September 2017 22:05
Erin Onat
Kevin, The clarification you pointed out is vital, and I have updated my post to be more explicit about this point. Thank you for... Read More
Tuesday, 19 September 2017 16:54
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Scott Lang

Start your engines! Modeling an Inertial Pump Startup

There are many (six!) ways to define a pump transient event in AFT Impulse. This gives you great flexibility in creating a model that behaves the way you want it to. One thing true for all pumps is that they must be started at least once. Pump startups often cause significant transient effects on the system so you may wish to model this with AFT Impulse. Even narrowing your pump transient down to a startup, there are still four models left to choose from: Without InertiaStartup With Inertia and No Back Flow or Reverse SpeedStartup With Inertia - Four Quadrant, Known...
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Scott Lang

When to Begin? Time and Events in Transient Studies

To define any transient event in AFT Impulse or AFT Fathom XTS the application must know when it begins. To do so, the user should know how time and event logic is approached in AFT’s transient solvers. In this article, we will discuss the three different time bases used in the applications, the selection of a single or repeating event, and the many possible triggering events that can start the user defined transient. The user defines these items in the Initiation of Transient section of the junction’s Transient tab. The requirements for each junction can vary, but the general approach applies...
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Erin Onat

Inherent vs. Installed Control Valve Curves and How They Relate to AFT Software

As tech support engineers, we sometimes receive questions from users confused about what control valve characteristic curve (inherent or installed) they are inputting into AFT Fathom, AFT Arrow, or AFT Impulse. The inherent control valve characteristic curve plots the valve open percent versus the percent of maximum Cv. This curve is true regardless of the system effects on the valve. The installed control valve characteristic curve plots the valve open percent versus the flow through the valve, and this plot is dependent on the conditions specific to the system. For example, if the control valve flow setpoint is fixed at 250...
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Dave Miller

Tolerable Convergence

Trying to design and analyze piping systems can be a complicated, and difficult task for engineers. This was especially true before the advent of easily accessible computer technology. Hand calculations required hundreds of hours of painstaking work, by entire teams of people. Great care had to be taken to ensure the reliability and accuracy of the results. Human beings do make mistakes, after all.

In today’s engineering world, there are a multitude of computer tools designed to make the design process simpler, faster, and more reliable, such as AFT’s family of analysis products. AFT products revolve around graphically based, drag and drop interfaces that makes creating a computer model of piping systems quick, and easy. Being able to create simulation models with little effort, however, can be a bit of a double-edged sword.

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