By Eric Parvin
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LMTD is a simple app to calculate the Log Mean Temperature Difference for heat exchangers (general heat exchangers, so shell & tube, fin fans, etc...). This app currently only works for 1-shell pass and tube passes of an even integer value (e.g., 2 tube pass, 4 tube pass, 6 tube pass, etc...). Since calculating LMTD with a calculator takes some time, and is prone to some simple errors, this app was developed where you just input the temperatures in and out, and it calculates it for you. You also input the number of shells you have in mind, and the number of passes per shell.
What's more, this app also calculates the shell and tube correction factor ("Ft"), and advises whether you need more shells. It then multiples the two numbers together to give you the corrected LMTD for an exchanger. This is especially handy when trying to troubleshoot exchanger performance, predict internal pinch (with Ft lower than 0.75 - 0.80), and determining whether you could gain significant performance gain by going from one shell to two, or 2 to 3, etc...
The program has built in messages to advise of bad user input values (like pinched out temperature conditions), whether the Ft factor is too low, or other common input errors. It also flags when there are some confounding conditions with the equations (e.g., when the temperature differences on the hot and cold side are exactly the same).
Simply input the Hot Temperatures (Th (in) and Th (out)), Cold Temperatures (Tc (in) and Tc (out)), and the number of shells, and hit "calculate", you got it.
You must hit the "calculate" button each time after entering new values. This was done intentionally to keep error messages from popping up all the time.
Heat exchanger sizing is not part of this app, just LMTD and corrected LMTD, or "ELMTD". Exchanger sizing will come from us in the not too distant future.
All values are estimates and should not be used for actual sizing, just for quick troubleshooting and estimations, please use validated software for this type of engineering work when designing equipment.
Visit the URL site for contact information to submit advice or any bugs found (none expected).
What's New in Version 2
Tabs for Celsius and Farenheit (although you will figure out the only difference is the letter F and C, all the math is exactly the same with the same inputs).
Added an entry field for you to enter the number of passes per shell for iPhone and iPad.
For iPad only: Made the iPad screens larger text for easier use. Added a message to iPad version only stating how much LMTD improvement you would get if you added a new shell.
- USD 0.99
- Category: Productivity
- Updated: 02 December 2011
- Version: 2
- Size: 0.1 MB
- Language: English
- Developer: Eric Parvin
- © 2011 ParV Enterprises
Compatibility: Requires iOS 4.3 or later. Compatible with iPhone, iPad, and iPod touch.