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Mass imbalance with fixed values (euler-euler)

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Old   April 6, 2018, 08:12
Default Mass imbalance with fixed values (euler-euler)
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Cees Haringa
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Hi all,

I'm modeling a bubble column with an external cooling loop. The external cooling loop is located such that no gas can enter.
To force a fixed flowrate through the loop, I set a fixed velocity in a small section of the pipe. When I run the simulation, air starts to be generated in this small section out of nowhere; the entire loop is filled solely with liquid, except for this small location with the fixed liquid velocity. This happens both in transient and steady state simulations. It happens both when I add a non-zero fixed velocity value for the liquid only, and when I do so for both liquid and gas. (When I only set a fixed velocity for liquid and not for gas, my liquid velocity soon exceeds light-speed. Which is not necessarily desirable either. It does appear to fix the mass imbalance however) It happens regardless of the discretization scheme for volume fraction

Does anybody have an idea on
A) where this issue is coming from
B) how to fix it?

Best regards,
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