Air dispersion in viscous liquid 2

[sasha121]

Hi, I want to foam up a polymer solution in an inexpensive manner, in a continuous process. I am thinking of intimately mixing air with the polymer at high pressure (10 bar) such that when the air/polymer mix exits the high pressure conditions the air expansion will cause the foaming effect. The viscosity of the polymer (before mixing it with air) could vary between 100 and 1000 cP. I am thinking of running about 10 volumes of air (measured at atmospheric pressure) and 1 volume of polymer though a 6 to 12" pipe fitted with a mixing shaft connected to a motor, the mixing shaft having several impellers similar in design to these

http://mixingimpellers.com/pricelists/rotofoil_weldedbl.html

The questions are:
1. Can this be done easier?
2. Is there a model that I can use to calculate the number of impellers /RPM needed to obtain good dispersion /small bubbles of air? (I’d prefer I didn’t have multiple passes through the mixer).
3. How do I estimate the required HP of the motor and torque on shaft and impellers?
4. Are there other issues I should take into consideration?

Any comments/suggestions would be much appreciated. Thanks!

 

[BigInch]

If you release it too fast you'll have an explosion. Ghost Busters comes to mind. Control the release well.

It sounds like too much air, as if you release it to atmospheric pressure you'll have air bubbles 10 x as large as when it was mixed with the polymer at volume ratios of 50/50.

Whether it will foam when mixing and flowing you'll have to check the 2 phase flow regime. What could happen in the pipe is that you could get something like polymer flow down the wall and air flow in the center of the pipe and they'll both flow at different velocities, or other strange effects you don't want. So, I've got no idea if it will foam or "extrude" in the pipe.

Power required for air injection? Just refer to the compression equations.





**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[sasha121]

Thanks BigInch, 10:1 does sound like a high ratio, and I'm certain I'll have to tweak around with it once I have a setup going. I don't expect to have all the air dispersed in the polymer (I'd be happy with half of that air to be entrapped in the solution).

 

[btrueblood]

BigInch's comment on air entrainment does ring a bell. A rotating mixer is likely to create the conditions he describes. A better option may be to use a (series of )static mixers (google the term), you may be familiar with small versions of the devices packaged with two-part epoxy glue dispenser syringes.

 

[stanier]

Perhaps you could look at the technology used in a dissolved air flotation p (DAF) plant for the waste water industry.

A book that may add some light Bubbles, Drops, and Particles in Non-Newtonian Fluids, Second Edition
R. Chhabra

 

[HEC]

for the gas dispersion why not use a sintered filter/silencer to create the dispersion and bubble size required. This will eliminate the need for rotating components and they can be manifolded to get the correct distribution/surface area required.

Mark Hutton

 

[IRstuff]

Seems to me that any mechanical process will be extremely difficult to control and potentially will result in gross nonuniformity in dispersion.

Have you considered a chemical means, similar to how styrofoam is made?

TTFN

FAQ731-376

 

[unclesyd]

Take a look at systems by Komax for gas/liquid contacting. This system works well in any pressure environment, especially pressure. We had one working at 450 psig with essentially a non-newtonian fluid.

You might give them a call with your exact requirements.

http://www.komax.com/Gas-Liquid-Contacting.html

 

[sasha121]

Lots of insightful suggestions, many thanks to all.

A sintered filter would work marvels in this case; my concern would be that the medium I would need to use it in would likely clog the filter after the first use. But it's definitely worth giving it a shot. Thanks!

The DAF technology looks a lot like what I had in mind. It will be on my soon-to-have-a-better-look-at list.

Perhaps this detail would be more revealing: I am not trying to obtain a stable foam, a 3 to 5 minutes life would probably be sufficient. The purpose would be to lower the viscosity of the polymer in order to obtain good coverage of some solid particles when mixed together. For various reasons I cannot increase the temperature or use a solvent/thinner.