Swedish DIY venturi

Should the CO2 be introduced at the throat, just before the throat, in the straight section before the throat, or does it matter? For that matter, I still don't see the theory behind why a venturi results in microbubbles of CO2. But, this is certainly a simple, elegant way to make a venturi, and a venturi that should not result in much of a head loss.

 

Venturi Design & Affect

A proper venturi is not as simple as a tapered pipe. There is a disproportionate difference in the angle of the taper IE: 90* input taper to 47* output to create a pressure differential to fascilitate the vacuum . This is merely an example as the taper is dependent on volume, and pressure.

Like wise there will also be a difference in the gas intake for Low pressure systems (Powerheads). IE: a quarter inch air intake might benefit from a .036" orifice on the leading edge of the air intake to compensate for lower static head pressure.

I'll provide a more specific example as time permits as I'm presently experimenting between proto-types designed specifically for use with powerheads, and Co2 induction. HTH. Prof M

For the record: The Mazzei Injectors are definitely worth the price, but are designed for high pressure sytems. Given their efficiency they still work splendidly for powerheads. Just not as well. A simple modification to the gas intake throat makes quite a difference, Though the machining is somewhat tedious.

 

Co2 venturi design

Yes the induction of Co2 as opposed to air is an entirely different matter as well. 1/4 " line is fine all the way up to the last orifice into the venturi. It allows you to offset the .036 opening to the leading edge. This increases the velocity of the gas flow when using power heads at a 150 to 180 gph flow rate. A very small augmentation to the gas flow produces a much finer mist, and allows you to maintain what precious little flow you have ( The flow rate is perfect for the reactor, but has a low static pressure as it relates to venturi performance).

I use this intake in a recombinant fashion to purge the reactor. Your original design was more than adequate for most systems. The short comings were always in the powerheads themselves. A longer reactor tube can handle the increased flow rate, but the escaping mist is actually a perk in my book. Now if you modify an internal duct within the reactor tube (Mixing Condenser) you can compress the stream for a more efficient exchange of gas, but it's really a mute point as the reactor is quite efficient already. Not many people push more than 180 bpm.

Venturi injection for Co2 is not really tricky, but it's considerably different than o2 or o3, and freshwater doesn't enjoy the same luxury of density as saltwater. Prof M

Your method of tapering the 3/16" pipette is much simpler I just have to figure out how to orient it within the venturi orifice ? A proud edge to the orifice would increase the vacumm energy !

 

From the Wikipedia reference: "A venturi can also be used to mix a fluid with air. If a pump forces the fluid through a tube connected to a system consisting of a venturi to increase the water speed (the diameter decreases), a short piece of tube with a small hole in it, and last a venturi that decreases speed (so the pipe gets wider again), air will be sucked in through the small hole because of changes in pressure. At the end of the system, a mixture of fluid and air will appear."
Or, to paraphrase: A venturi works to mix fluid with air by working to mix fluid with air. That isn't an answer. My question is why does a venturi produce microbubbles of CO2 which is introduced where in the venturi? I know very well how a venturi is designed and how it works as a venturi, having designed several many years ago to measure flow rates of both air and water, but I don' t know why it works to make microbubbles of CO2, and not knowing why it works, means I have no idea how to make it work better or best or well enough, etc. In principle, the lower pressure at the venturi throat should result in big bubbles at that point, which become smaller bubbles when the pressure goes back up in the downstream part of the venturi. But, that wouldn't by itself produce micro bubbles. In fact if you introduced milimeter size bubbles in the approach pipiing to the venturi, the bubble size in the outlet tube from the venturi should be almost exactly the same, because the static pressure will be almost the same.

 

If you are using a venturi to measure a flow rate, and callibration is very difficult, then and only then is it critical to optimize the inlet and outlet forms for the venturi. That lets you use theory to determine the flow rate versus the pressure change from inlet to throat of the venturi. But, for any other use, a simple smooth transitiion from the inlet diameter to the throat diameter is just fine, and the exit transition from the throat to the outlet diameter only needs to be gradual enough to avoid flow separation, which would result in a big pressure drop across the whole venturi. So, for our purposes - to produce CO2 mist - all we need is a simple venturi with a smooth transition at both ends to and from the throat to avoid pressure losses.

But, how that produces CO2 mist remains a mystery to me.

 

On the Contrary

The Transition of the tapers are in fact critical to the performance. (Compressing, Drafting, Swirling and Re-expanding ) Either will provide a venturi Affect, but one will provide better (Sustained) performance. Due to the difference in the density of Co2 a smaller gas orifice is desirable, and this smaller mist is swirled into the impeller where it in turn cavitates to corrupt even smaller bubbles.

I'd be happy to provide a working model, and you can study it, and reduce your impression to an intellectual prose that suits your own taste. Never the less it does work rather impressively. You designed flow models. I designed injectors. Did you want to calculate the flow or inject a gas ?

Here's a link to a splendid design.

Mazzei Injector Corp. - How a Mazzei Injector Works

The only augmentation necessary for our purposes is to decrease and offset the orifice to adapt it to Co2. Basically machining or fabicating a drop in port to increase the intake velocity of heavy gas.

Venturi injection is mainly attractive for maintenance purposes, increased flow, and faster saturation.

Mi Dos Centavos, Prof M

 

I'd like to focus on a venturi design that does not use a reactor tube at all.

Seriously ??? I was playing with a venturi design using a mixing condenser prior to the reactor, and it relegated the reactor to a fairly useless state (Pretty much eliminated it) There was a slight affluent of micro bubbles, but not nearly enough to justify the reactor tube. IMHO just enough to compliment the plants.

The design required significant pressure. So I'm back tracking to the gas injection port to better accomodate Co2 at a lower flow rate suitable for powerhead applications.

It was easy to build an industrial model. The trick will be in accomodating lower head pressure suitable for smaller aquariums. Every design I've seen no matter how efficient has a feeble venturi, and the port was designed for O2. Drafting the intake prior to the impeller is only half right. Your diagram (90* Shear to the intake, and description of the tapered tubing is well on the right track, but a few accomodations for a proper venturi, and swirl might add 30 or 40% increase in volume, and saturation. I'll be sure and post plenty of diagrams right away so someone can relable it for production ! LOL.

 

I think my brain is finally wrapping itself around this better! It is the high speed of the water through the venturi throat that make it work so well? The rapidly flowing water rips the little CO2 bubbles apart as they squeeze out thru the orifice? That makes a lot of sense. Then as the flow slows downstream, the pressure rises, which shrinks the bubbles even more? If I have it right, the best location to inject the CO2 would be the venturi throat, where the velocity of the water is the highest. And the smaller the inlet orifice for the CO2, the smaller the entering CO2 bubble , making the shredded bubble the smallest.

Thanks for stimulating my mind with this!! Now I can visualize ways to use this effectively.

 

RE: Orientation Of Pipette

Got It ! Using the tapered pipette the inlet doesn't have to be offset. I just have to decrease the diameter of the opposing pressure well to the same diameter of the pipette, and keep the inlett slightly proud of the throat.

The use of the needle wheel impeller is even better, producing a much finer cavitation, and the ceramic bearings are a huge perk !

For a 1/2" flow the mixing chamber should be appx. 4 " long. Maybe 5" tops.

If the swirling veins are in the venturi, and the affluent is compressed. The reactor is eliminated...

 

Change of plan !

For the time being I eliminated the tapered pipette, and am using capillary tubes to modify the gas intake. This allows me precise metering of the gas, and permits me to adjust the height of the leading edge within the throat to increase or decrease shear pressure across the intake.

 

Yer tellin me !

I had to cut these to length with a 400,000 rpm disc ! Tweren't EZ !!! LOL. But now they're "Custom Parts"

FTR they're sheethed by a 1/8" polypropylene bulkhead.

 

Any Pics of your project?

 

Not Yet !

None yet Peter, I'm working with multiple formats at the moment. It's unlikely I'd post pics to the web just yet, but I have a few friends in Sweden capable of the fabrication. Where are you at in Sweden ?

I can try to translate to Swedish if you like. It may not help with the description, but it's sure to provide some comedy relief !

If you can tell me the diameter of the tubing I can calculate the tapers for you. Grtz. Prof M

 

If you mean my tubes i did ?

well the diameter inside of tube
1. is 21mm and in the middel(thin part of the tube) it 8mm

2. is 17mm and in the middel(thin part of the tube) is 6mm

Or you better translate in to swedish

Im located in the south part of sweden close to Malmoe.