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Erin Onat

Let the Heat Flow: Modeling Heat Transfer in Pipes in AFT Fathom and AFT Arrow

Among the many talents of AFT Fathom and AFT Arrow software is the ability to model heat transfer. While a major source of heat transfer is heat exchangers , this blog will address heat transfer that occurs in pipes. First, for the basics: Just what is heat transfer? Well, heat transfer occurs when there is a temperature difference between two objects at different temperatures. As all engineers know, the common theme of physics is that matter and energy alike travel spontaneously from higher, more chaotic surroundings to calmer, lower energy situations (not unlike the stereotypical engineer), and heat transfer is no...
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Abby Zimmerman

Bring the Heat: Modeling Heat Transfer in Heat Exchangers in AFT Fathom and AFT Arrow

Heat exchangers are some of the most expensive pieces of process equipment, so it is crucial that their pressure losses and heat transfer are well understood. AFT Fathom and AFT Arrow allow users to model heat exchangers within their piping systems. Pressure loss models include input K factors, resistance curves, or tube bundle information. When energy balances are being considered, users can choose between 11 heat transfer models in AFT Fathom and 12 heat transfer models in AFT Arrow to best meet their hydraulic modeling needs. While AFT Fathom and AFT Arrow can also model heat transfer in pipes , this...
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Erin Onat

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

Around this time of year with Thanksgiving just around the corner, I always 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...
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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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Abby Zimmerman

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...
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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...
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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 Inertia Startup With Inertia and No Back Flow or Reverse Speed Startup With Inertia -...
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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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