Flash calculations

Moderator: jasper

Flash calculations

Postby Stephan » 20 July 2022, 15:23

I have a flash unit operation in a testfile.
When I run it, the liquid outlet has a higher water flow than the condensed portion of the water in the inlet stream.
How can that be?

See attached file.
Attachments
Test Flash.fsd
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Re: Flash calculations

Postby jasper » 20 July 2022, 16:35

The document you posted seems to only contain compressor units - can you check whether you attached the right document?
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Re: Flash calculations

Postby Stephan » 21 July 2022, 07:10

Indeed, I atached the wrong file. Here is the right one.
Attachments
Flash Test.fsd
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Re: Flash calculations

Postby jasper » 21 July 2022, 08:49

At 1.634999 bar and 78 C, water is liquid. The vapor pressure for water at 78 C is 0.43703103 bar.

However, mix it with enough air and enough water goes into the vapor phase. Your vapor molar flow rate is 16.5x higher than your liquid molar flow rate. Water mole fraction in the vapor phase is roughly 27%, which, from a quick google search (https://www.engineeringtoolbox.com/maxi ... _1403.html) is not unreasonable?
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Re: Flash calculations

Postby Stephan » 21 July 2022, 11:47

Indeed, I was wrong.
I just misinterpreted the stream informations.
The flash unit behaves as it should.
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Re: Flash calculations

Postby jasper » 21 July 2022, 14:46

Glad to hear your issue is resolved.
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