Heat Exchanger doesn't converge

Discusses use of CAPE-OPEN compliant Process Modelling Components

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Heat Exchanger doesn't converge

Postby Stephan » 10 March 2021, 08:46

I have a co-current heat exchanger configured via LMTD.
However, when setting a value different from 0 W/K it failes to solve
(line search didn't converge).
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test HEX.fsd
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Re: Heat Exchanger doesn't converge

Postby jasper » 11 March 2021, 09:12

This is because the LMTD for co-current operation at zero heat transfer asymptotically goes to infinity (1 divided by zero, see here for the definition: https://www.cocosimulator.org/index_hel ... hanger.htm)
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Re: Heat Exchanger doesn't converge

Postby Stephan » 16 March 2021, 08:25

It also doesn't converge for heat transfer values > 0W/K.
Error message is the same as for 0 W/K.
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Re: Heat Exchanger doesn't converge

Postby jasper » 16 March 2021, 16:29

There is a problem with the PH flashes - it is being investigated.
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Re: Heat Exchanger doesn't converge

Postby jasper » 18 March 2021, 12:16

Please edit the Prausnitz COPP property package, and change these solve options:

Tolerance = 1e-9
Iterations = 300

Please confirm that this resolves the issue - default settings for new property packages are under investigation.
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Re: Heat Exchanger doesn't converge

Postby Stephan » 22 March 2021, 09:10

Changing those settings doesn't resolve the issue.

Furthermore, at some flowsheets thoses settings can't be changed.
Whenever I change iteration and accuracy settings within Chemsep
and try to save the file, values are set back to the defaults.
Depending on the file sometimes changing the accuracy only works,
in another file changing the iterations number setting only works.
In some files I can't change any of the 2 settings.
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Re: Heat Exchanger doesn't converge

Postby jasper » 22 March 2021, 10:09

I tried changing the settings myself and it does appear to work for me.

I can also not reproduce settings not restoring properly. If I change the settings and save the file, the changed settings persist correctly.

Can you attach a file and let me know the steps to reproduce the issue of persistence?
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Re: Heat Exchanger doesn't converge

Postby Stephan » 22 March 2021, 15:11

Pressing the Solve Button produces the calculation error.

When klicking Settings->Property packages-> Prausnitz->Solve Options
and setting accuracy from 1E-6 to 1E-9 it reverts back when saving the Chemsep file.
Attachments
test HEX2.fsd
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Re: Heat Exchanger doesn't converge

Postby jasper » 24 March 2021, 10:21

Can you check that this is the right document? This one has 3 embedded flowsheets and an incomplete thermo configuration - I was expecting something with a heat exchanger.
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