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100% of the total discrete phase mass was not tracked HELP

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Old   March 31, 2020, 11:10
Default 100% of the total discrete phase mass was not tracked HELP
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I am investigating the bubble sizing produced on a microbubble generator using DPM to track the bubble particles and noticed the following message.

"WARNING: 100.0000% of the total discrete phase mass was not tracked for the expected residence time:
0.00862 s less on a mass-weighted average (which is 86.1631% of their total age or 86.1631% of the last time step).
You may be able to reduce this discrepancy by changing the tracking parameters, that is,
increasing the maximum number of time steps used to compute a single particle trajectory."

Please could someone explain exactly what this means and how I can overcome this problem.

I am fairly new to using CFD software so it could be something simple I am missing?
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Old   March 31, 2020, 13:24
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There are multiple settings that could have gone wrong. The very first one is, as suggested in the warning, to increase the number of steps for DPM. This is available under DPM Panel. For steady-state, it should be set to at least tens of thousand, default in new version is 50000. If the simulation is transient, it should be at least 500.

Second thing you need to check is the direction of injection with respect to the domain and gravity. Since these are bubbles, so, these are supposed to go against the gravity. However, if gravity is not correctly specified or its direction is wrong or if the operating density is wrong (available under Operating Conditions), then bubbles may go in wrong direction.
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