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Two-phase flow in vertical line

Two-phase flow in vertical line

Two-phase flow in vertical line

(OP)
A stream of carbon dioxide gas is injected into a vertical line (probably 10") where water is flow down. The idea is that the water flow will carry/dissolved the carbon dioxide gas with him. I am looking for a correlation that predict the vertical line size so all the gas will derived vertically down with the water and no gas bubbles will traveled up.

Thanks in advance,

Mike

RE: Two-phase flow in vertical line

Balance velocity in water drag on an assumed spherical bubble vs weight of water displaced by the bubble, you'll have a stationary bubble.  Any faster water velocity will drag the bubble down with it.  I doubt it will take too much water velocity to do it as long as your injection rate is reasonable in relation to the water flow passing.  Take a look at your gas to water flowrates and compare with 2 phase flow regimes to see what form of flow is predicted for your mixture.

But I think that will not guarantee the CO2 gets dissolved.  It will only get you bubbles moving down. The rest is contact time, pressure, temperatue, diffusion rate, solubility and resulting pct concentration.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Two-phase flow in vertical line

The classic reference for this problem is the article by Larry Simpson from Chemical Engineering, June 17, 1968. Basically you need to get the Froude number for the water correct. The more usual problem is to keep the flowrate sufficiently low so that the bubbles can escape upwards.

If the Froude number is less than 0.31 then bubbles will escape upwards. As you increase the flowrate (and therefore the Froude number) the smaller bubbles will be swept out until you reach a Froude number of 1.0, at which stage you basically have a syphon and all the bubbles are swept down with the water.

For a 10" pipe the water flowrate at this point (i.e. Fr=1.0) would be about 1250 USgpm, or a velocity of 5.1 ft/sec.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: Two-phase flow in vertical line

(OP)
Thank you all. The issue that puzzles me is how the Froude number is related to tow phase flow regime?  For example if the flow is bubble how this affect by the Froude number?   

RE: Two-phase flow in vertical line

The question is:  Is this a mechanical (ie Froudle number) problem or a mass transfer proble (ie solubility).

If you go with the mechanical, then you'll understimate the amount of CO2.  If you use just the solubility, you will over estimate because you can't get to equalibrium without mixing.

The solution would be a "column" with mixers or packing. Then do an absorber calculation.

PS, you'll see a rise in temperature.

RE: Two-phase flow in vertical line

The Froude number is a ratio of the liquid velocity to the density difference between the liquid and gas.  It seems reasonable to me that that ratio would affect the direction the bubbles move.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: Two-phase flow in vertical line

dcasto - Yes, the Froude number will only indicate whether the bubbles move up or down.  It gives no indication of the rate of solution of the gas into the liquid.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

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