Calculation of vertical waterflow caused by air bubbles

Question

Calculation of vertical waterflow caused by air bubbles

magnusrm (Mechanical)

(OP)

6 Sep 17 13:32

Hi guys.
Im working on a project where we need to estimate vertical flow in a wide vertical tube caused by a stream of air bubbles released at the bottom. I have Solidworks Flow, but this is as far as i understand not suitable for this kind of calculation.
Do you have any tips to the easiest ways of calculating this? My goal would be a way to calculate vertical water current speed (distribution) based on:

Diameter of tube
Height of tube
Air bubble hole pattern (number and placement)
Air hole size
Air pressure

I have looked abit at OpenFOA`M, which might be an alternative?
Hopefully I could get out some sort of relation which could later be processed in Excel, so that I dont need to run a CFD 100 times.

Thanks!

hendersdc (Mechanical) · Answer 1 · 2017-09-06 16:37:05

In a sufficiently wide tube there will be no vertical flow of water, the water will just get out of the way of the air bubbles. I'm not really sure what you are going for with this but I am reminded of an ejector which uses high pressure flow of one fluid to induce flow in a secondary fluid. I don't know how well this would work with air and water but here is a link to a paper that describes ejector design in detail: http://www.academia.edu/9013956/EJECTORS_AND_JET_PUMPS_-DESIGN_AND_PERFORMANCE_FOR_INCOMPRESSIBLE_LIQUID_FLOW

IRstuff (Aerospace) · Answer 2 · 2017-09-06 16:53:47

From a 10 kft perspective, there can't be a net flow; if you left the top open, the only thing coming out is the air from the bubbles. There's possibly a circulation current around each bubble.

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3DDave (Aerospace) · Answer 3 · 2017-09-12 08:40:46

If I understand right, this is how air lift pumps work; they have a tube in the water with a bubbler at the bottom to entrain water and to lower the bulk density. The combination of entrainment and density loss causes the water/air mixture to flow up the tube.

To simulate this either you need a vast number of bubbles and a time-phase solution or a way to have a phase change that alters the density of the liquid in the bubble column.

Interesting video: https://www.youtube.com/watch?v=TOVZ4oklBFw In the video it is used to recirculate as a demo, but with enough density change it can lift water to a height equal to the depth. I think these are also used as under-water 'vacuum' cleaners.

broadtechengineering (Mechanical) · Answer 4 · 2018-01-09 13:13:32

In your case, I believe that the multiphase flow analysis is a big part of your CFD fluid simulation.
I highly recommend setting up a controlled experiment to better have a better physical understanding and as test cases for numerical and theoretical work.
In addition, to recreate some important simulation models and engineering modeling techniques, it is critical for you to measure the key parameters involved in the two-phase bubbly flow such as bubble shape, bubble motion, flow regime which play a considerable vital role in many engineering simulation applications.

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