Tiny bubbles

Are you planning to bottle your own soda water? If so, it will be a lot easier for you to buy a commercially produced kit than to design and build your own from scratch. And if you're not, the commercially produced kits might still be suitable for whatever purpose you have in mind.

Try looking at a fish aquarium oxygen aerator.

They have been designed to be very efficient at producing the right size bubble to dissolve oxygen into the water.

John.

Check companies that sell air diffusers for sanitary waste treatment plants. They will usually provide technical data for product application.

The information you want is easily available. their was a lot of work done onthese problems between the two world wars. Have a look in hydraulics and chemistry textbooks of that period and later, particulaly English and German texts.

the swedish and german submarine companies both use co2/water diffusion in their submarines so they may have some papers too.

I played with it years ago. the major problem I had was obtaining even flow over the sparger surface. with anything other than a flat exchange surface the bubble size varied due to depth variations.

I did have some success by using a two stage process - first stage sparges gas into liguid at several atmospheres, gining pretty well complete dissolution; the second stage two releases/diffuses the high pressure liquid into the atmospheric tank. you can graduate the process by using a tall tower (32' per atmosphere). highly polished contact surfaces on the container with a LOWER temperature to the fluid helps retain the gas in solution.

hope this is helpful. Sorry i have forgotten my references, it was over 30 years ago.

You might also look at CO2 absorption processes (such as air rebreathers use) then dissolve the absorbant material in water???

Hi there Paddler

If you are not talking large quantities, it could help to keep things at low temperatures. Potential D.O concentration of cold water is higher than in warmer water and CO2 should react the same. Frost the sparger if need be. I suppose.

Good Luck. Ky.

Paddler, I may have a few leads for you. You have probably already found the disc diffusers at Stamford Scientific? Something to consider. However, since they work by stretching a membrane with slits, I suspect the bubbles are not going to be small enough for you, but have a look.

Second is the sintered metal filter media from GKN Sinter Metals. In particular, have a look at the Spargers page AND especially the SIKA-R ...AX media. They can produce thin sintered discs with pore ratings from .5 to 200 microns. I suggest that you download the first brochure listed at this page and have a look at page 5 of the brochure, which gives data for the various sintered media. Particularly useful is the bubble point data.

This GKN literature gives the bubble point pressure in isopropanol for the various sintered media. This is the threshold pressure for creating bubbles. This pressure P is related to surface tension and bubble size by the equation P = 2(γ)/r where γ is the surface tension of the liquid and r is the bubble radius.

The surface tension of isopropanol at 20 degC is 23 dyne/cm. So for example, for the 10 micron rated media, p = 23mbar = 23000 dyne/cm2. Thus the bubble size in isopropanol should be about 40 microns. Allowing for the difference in surface tension between i-PrOH and water, the bubble size in water should be no more than about 125 microns (~1/8 of a millimeter) for the 10 micron media. These would be quite small bubbles. The typical limit for human vision is about 40 - 50 microns BTW.

I believe that this use of the bubble point pressure to estimate bubble size is correct. I have asked GKN to confirm/comment via e-mail, but have not received a response back yet.

I hope this helps.

jhammond

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www.patent-innovations.com

Although the Biotech industry uses this process for a different purpose, there have been a lot of studies performed with varying types and sizes of spargers. I would try the ISPE or ASM and see if they can provide you with any data. Some of the studies I have been involved with are strictly propietary, an unfortunate result of a highly competitive industry.

What you saw in films etc., are probably the design for "tiny bubbles" that are required in DAF units.

Perhaps if I share my experience with Boyle's Law and the behavior of tiny bubbles within an area of liquid, we might get to a point of progress. I am not sure my advice will lead to THE solution. You may find it helpful.

I recall that it was less efficient to force air, gas, etc., into the liquid than to stir it into the liquid. The liquid in this case...(my past experience), was a wastewater lagoon. We needed to aerate it efficiently. Our desire was to use the least energy to inject tiny bubbles and keep them entrained within the confines of the lagoon.

A highly efficient Eaton Aerator was used to accomplish the task. We were pleased with the efficiency. The unique aerator has an air screw at the water surface. A 25 horsepower electric motor...(Baldor or Reliant), was used to drive a stainless steel down-shaft, which had angular blades from top, near the air intake, down to the impeller. The impeller is a uniquely designed part, installed at the lower end of the down-shaft. Influence of the aerator was at least 90 ft. diameter. The sheering action of the angular blades kept the bubbles small. The unique impeller sent the bubbles out to far sides of the lagoon. We benefited from gas converting microbes within the billions of tiny bubbles to accomplish conversion which was our goal.

My company, Trident Environmental Services & Technologies, often has a goal of converting characteristics of lagoons and biomass. We found that we were able to clarify the lagoons, bringing pH to about 7 and removing foul odor. This was accomplished within a few hours time.

We may be able to assist you with a system design improvement/change.

JOHN WEAR, Pres., Trident Environmental Services & Technologies www.tridentworld.org

Thank you for all the comments. I have started to get responses from sintered metal suppliers but no performance data.

The application is for (slight) pH control in water that started as rain and flowed over limestone, shells and concrete culverts. An existing discharge permit has very tight pH limits in an environmentally sensitive area. In certain dry and wet periods the pH can get very close to the permit limit.

CO2 is diffused into the water outlet to bring down the pH. The water is hot due to ambient conditions and sun heated ground (>100 deg F). I have looked at the solubility via Henrys law constants and both CO2's disassociation constants and remain convinced it will work.

My problem is that the "ditch" is shallow and large bubbles rise to the top without time or surface area to transfer mass of CO2 from the gas to the liquid. Hence the interest in tiny bubbles.