Hybrid venturi/vortex aeration system for RDWC

[Northern_Loki]

It certainly seems to do well on the DO, at least what I’ve measured so far. I have yet to evaluate the DO using the venturi + needlewheel during a grow cycle to validate the applied performance to the DO but I’m fairly confident that it’ll do well comparatively.

I think I read about the vortex technique being using in some scientific journals where the main end-application is for the aeration of large bodies of water. From what I recall, it has been shown to be an efficient technique.

The majority of the DO experiments that I’ve seen in the various forums, using the various techniques such as waterfall, air stone, etc, have run the experiments stand-alone. But, they have not measured the DO while the plants are in the system. The rate at which DO is depleted and the rate that the DO is replenished in actual application, I think, could be illustrative.

[slain]

Yep vortex aeration seems what they use in water treatment plants and large fish farms (along with large venturi aerators) where sparging with air stones is not practical. The studies I have read it is just as or more efficient in comparison to any other method and I like the simplicity. And what’s not to like about a stable whirlpool?
For Mk. 2 I was thinking I make a taller and narrower vertical tube so the vortex is both higher and faster, this obviously increases turbulence and water/air contact time so it ‘should’ be much more efficient. For this experiment I just wanted to see if it was straight forward to get it circulating with a stable vortex. Turns out to be easier than expected. I have a 2 bucket system I have to setup for a friend on the cheap. I am thinking he might be the perfect crash test dummy

For even distribution of water/air to the buckets I have previously set up a system as your diagram indicates, however the I fed the circulation pump output into a central 6 inch ‘manifold’ pipe ( just regular 6 foot long PVC drain pipe) that was capped on each end and had an 1 inch outlet plumbed in for each bucket. The pump outlet connects to a inlet fitting on one end of the capped pipe. Then a 1 inch tube connects the manifold to the bottom of the bucket, so you get the nice upwelling effect I see in your video. The manifold works exceptionally well at balancing pressure so the buckets all fill and drain at the same rate.
I put an overflow at the top of each bucket that is plumbed so that it gravity feeds back into the rez. This setup still uses an air pump but I think If I used one of these skimmer pumps I could potentially get rid if the air pump altogether.
I would be very interested to see how fast the oxygen is consumed by plants, I can’t see it being any more rapid than fish would deplete it I would have thought?

[slain]

Looking at those pin wheel pumps, it occurs to me the pinwheel idea could just as easily be passive and do the same job of breaking up the bubbles. As in the water upstream of the pump could simply be forced through a pinwheel impeller. Then the pumping could be done with a more efficient impeller design, you would be able to push more water around and therefore suck in more air. I just disassembled one of my submersible pumps to have a look and it woudl be reasonably easy to modify it to perform is a similar way. Am thinking I might have to fire up the 3d printer.

[Northern_Loki]

Your experiment deserves it’s own topic…

@slain

therefore suck in more air

Yes, the higher the velocity past the venturi, the higher the vacuum potentially generated.

@slain

could just as easily be passive and do the same job of breaking up the bubbles

I’d agree, the smaller the bubble size, the better.

I don’t think a passive technique of breaking up the bubbles would be able to create as “small” of a bubble size, though.

For some aquarium pumps, you can purchase the different impellers (including pinwheel) and swap them out. FWIW.

[ATM]

I just use 2 power heads in a 20 gallon res. No need for airstones and I don’t use the air feed. The circulation is all that is needed.

[Northern_Loki]

For reference, here are a couple of plots from some tests I did last year on DO (no plants) under different operating conditions:

For these, there were four modes of operation:

1. pump speed set to low with the venturi off.
2. pump speed set to high with the venturi off.
3. pump speed set to high with the venturi injecting air.
4. pump speed set to low with the venturi injecting air.

The initial “high” DO is from the municipal source supply, which, as can be seen, eventually out-gases. Just having the solution moving and fluming does not necessarily saturate the DO by itself. Oh, take the plots with a grain of salt since getting accurate/repeatable readings of DO takes a bit of detail. During some of this collection I was still getting acquainted with what to do/not do. Just thought you might be interested in seeing those.

The data collection and testing that I was working on (with help from @anon32470837) was put on pause “temporarily” as I had more pressing items to work on. But, now that I see you’re looking at venturi injection, my interest has been peaked again. I’ll probably look to get back to experimenting with this in the near future and to compare notes.

Side note, I was also doing some experimentation with the addition of surfactants to the solution along with the aeration. That has some potentially interesting results, as well.

[slain]

That is so freaking cool. So in your plot ‘air’ indicates the active venturi? Interesting you got slightly divergent results at the end of the plot with the pump on low, I wonder what that’s all about? It’s obvious this is fully saturating the water, and given it’s going to hold the same amount of oxygen regardless of the aeration method it’s hard to see how this won’t function every bit as well as any air pump. It’s not like there is much of a lag in oxygen uptake even. It woudl be really interesting to see this next to a airpump aerator.

Having now spent a good few hours looking at venturi design and pinwheel pumps, I am thinking I might have a crack at making some in Inventor and 3d printing them out. I have a 10000Lph pump with busted impeller that would make a great bubble thrasher.

II found a reasonably good technical paper on the “analysis on the effect of venturi tube structural parameters on fluid flow” which runs a number or test on the elements that influence both velocity of fluid flow and probably more importantly vacuum.

https://aip.scitation.org/doi/pdf/10.1063/1.4991441

It’s fairly maths heavy if you want to really get inside the actual fluid dynamics of it all, but you don’t have to in order to glean a lot of useful information. I sure wish I had paid more attention to fluid dynamics when I did engineering!

[SuperiorBuds]

I was staring at all of my different airstones and diffusers the other day and I thought – I really should do a comparison of these to see which one works the best at aerating the reservoir. Unfortunately I don’t have a DO meter right now so I started looking around to find one.

Any suggestions, @Northern_Loki? Cheaper is better but I would take accuracy over cost.

I also have my venturi from my E&F setup so I could do a good side by side by side comparison. I’d love to see time to total saturation for each of these so we could truly compare. I know the venturi worked well for me last time, but there’s more data to consider here and I’d love to see it all.

[beacher]

A friend has used a similar but more basic system for years. A water pump circulating the res. The intake line for the water pump sits on the bottom and has a small tube branching off that goes above the surface to get air.

I wouldn’t say it makes a vortex, but a ton of air gets in there very simply and cheaply.

Interesting design!

[ATM]

Um. Wow. Just to take the effort to do this. Now just do a run in each of these scenarios and see how it affects yield. Haha. Just kidding…good work.

[Northern_Loki]

@slain

So in your plot ‘air’ indicates the active venturi?

Yes, correct. The venturi, in this case, is nothing more than some polypropylene tubing jammed into the pump feed line with a value to meter the air inlet. I need to construct something better than just a tube.

@slain

given it’s going to hold the same amount of oxygen regardless of the aeration method

Part of what I was trying to evaluate was whether we could super-saturate the DO. From the trials, I did see positive signs of super-saturation on the order of several percent. But this needs to be re-evaluated carefully as I also saw some conflicting/confounding measurements (as can bee seen in the graph trends).
Yes, it is possible to achieve >100% saturation using active methods. Which techniques to use, and within our grasp, to achieve that is the question. The extreme end is nano-bubbles that collapse in solution under pressure achieving a DO that is much much greater than 100%.

@slain

it’s not like there is much of a lag in oxygen uptake even

@slain

it’s hard to see how this won’t function every bit as well as any air pump

I agree, I think other mechanisms will easily compete with airstones. And, could end-up being less costly along with other benefits.

So, for those graphs, they have a fairly long time scale. When the venturi is allowing gas into the system, I was seeing about 30 minutes to fully saturate 40 gallons of solution. It is fast relative to fluming (air off). We need some other experiments to see if there is actually any merit here versus vortex, airstones/air pump, waterfall, etc, etc…

@slain

I am thinking I might have a crack at making some in Inventor and 3d printing them out.

Very interesting. Looking forward to seeing how this works.

@slain

II found a reasonably good technical paper on the "analysis on the effect of venturi tube structural parameters

That is awesome, I need to study this. Thank you.

[Northern_Loki]

Data geeks unite!

So for DO probes, there are two primary types. Polarmetric and luminescent(LDO). The preferable type is luminescent. Polarmetric is touchy, sensitive to solution velocity, and drifts. But, it also the least expensive.

What I have is a Hatch LDO probe along with a Hach meter. Their stuff is very expensive although, by being patient, these can be had via Ebay. I ebay’ed a used LDO probe and simply purchased a new LDO “cap”. From what I recall, I was able to get the probe for ~$100, the replacement cap ~$100, and the meter for ~$200. So, yeah, even used it is pricey. If you are willing to spend some sweat equity, industrial meters/probes can sometimes be had on the cheap.

A polarmetric Milwaukee DO probe + meter are available for under $200. There are downsides to the polarmetric method but may be perfectly suitable depending on how it’s going to be used.

For on-line process, the newest generation of LDO require no calibration ($$$), Hach LDO® Model 2. But, money to burn?

For what I’m doing, the probe needs to stay stable for long periods of time while submersed. LDO is better for that. And, I can say that DO probes in general are a bit tricky to use/understand in practice.

@SuperiorBuds

I’d love to see time to total saturation for each of these so we could truly compare.

That would be excellent. If we can get folk with various set-ups measuring the DO %, rates, plants in-situ / ex-situ, we’ll have data that well exceeds what is currently available on the interwebs.

Understanding, measuring this is fairly difficult and expensive. It requires a certain amount of data geeky-ness to get sensible results. Right now, viewing the past experiments available from other sources, I feel their results may be a bit “misleading” as they avoid looking at things like saturation rate, etc. A comparison using an improved experimental methodology would be valuable.

[Indiva710]

If someone wants to let me borrow a meter I would have zero problems getting some data for the interwebs…and considering I have several different setups and I would like to know how they run vs each other…as I have a superponics cloner which is a dwc with top feed…I’m building a new cloner which will be done in 2 days when all the parts get here which it will be low pressure aero and fogponics too…so I can of course do one or the other and both…my veg setup is current culture rdwc but it’s upgraded and im running a alita60 with 2 large air stones per bucket for a 4 site 8gal…and my bloom setup is 4 site rdwc 27gal totes 3in pvc waterfalls I have x2 350gph pumps and my return pump is a 700gph 3in pvc I also have a drain kit I built which leaves 200ml in ea tote only…same setup for veg for the drain kit which they help with circulation to…so if anyone has a d.o meter that would let me borrow I wouldn’t mind getting data for everyone

[anon32470837]

@beacher

A friend has used a similar but more basic system for years. A water pump circulating the res. The intake line for the water pump sits on the bottom and has a small tube branching off that goes above the surface to get air.

I wouldn’t say it makes a vortex, but a ton of air gets in there very simply and cheaply.

Excellent idea!

I have been trying to keep my rez cool, so I am using an ice chest and adding frozen water bottles. But, with the ice chest lid closed up tight, the rez wasnt getting enough fresh air, and the water got nasty. Ive been playing with different ways to allow more air in while keeping the light out and keeping things cool, but none of them worked perfectly.

I have a 300 GPH aquarium pump fluming the rez. After reading this thread, I just stuck a section of air line tubing in the intake of the water pump, and ran it out side the ice chest through a small hole. Now it sucks in fresh air through that small tubing and the impeller in the pump breaks it up into small bubbles every time the pump runs. Extra freash air with no light contamination and I can keep the ice chest sealed tightly for less heat. The bubbles are not as small as you would get with a needle wheel impeller, but good enough for what Im doing. About the same size you get from a regular air stone.

[GrapeApe]

Add a pvc drain pipe that drain from the top. Like a over flow on an ebb n flo table. Then insert venturi valve at the bottom. It creates a wicked venturi effect.

[Tappy]

This whole conversation is super cool…I’ve heard of the venturi effect before, but never looked into it.

What types of degrees do you guys have?..lol

[slain]

Haha well I’m a systems engineer so I basically mess about with experimental stuff for a living. I have a mate who is setting up a 8 pot dwc, so I am going to attempt to build one of these vortex venturi’s that hopefully works in a real world setting,
note… it’s not MY setup I am game to experiment on this with I’ll post some pics of it when I do.

[cannabissequoia]

@Tappy

I’ve heard of the venturi effect before, but never looked into it.

Just stare at a bong!

[SquirtleSquad]

I wanna experiment with this in a RDWC setup.

I’m worried about burning the pump out with so much restriction on the discharge.

I plan on using a 1000GPH that takes water from control bucket and dumps the water into the totes from a waterfall. This is where I was thinking of install a Venturi. So water would go from the control to a manifold which has branch run-outs to each plant site tote. On the branch run outs would be a Venturi to an elbow down through the tote lid and waterfalling on the water surface.

Water returns to the control via 1" barbed bulkheads and 1" poly.

The branches are 1/2" so not sure how much more I can reduce that for a Venturi effect.

This is the easiest way I see it working with my existing setup.

I first thought of using the barbed bulkheads as the discharge and doing away with the waterfalls and drilling holes mid way on the totes and returning to control bucket via that.

[anon32470837]

You dont really need a restriction in the water line to have the venturi work as far as sucking air. The restriction is there to force the water to flow faster, which will create more suction than withoout a restriction, but you can get suction just fine with no restriction to the water flow.

Just stick the air line in at a slight angle towards the direction the water is flowing. It also helps quite a bit if you can position the venturi up as hi as possible so there is no static pressure from the water colume that has to be over come.

If you have the venturi on the floor for example, then when you fill the buckets, there will be several inches of water above the level where the air needs to enter the system. That creates pressure and forces the water up into the sir line until its at the same height as the water in the bucket. Then when the venturi starts to work, it has to over come that pressure before any air can start to enter the system.

Instead, position the venturi as hi as possible relative to the ‘full’ or maximum water height in the buckets. That will let the venturi work at max efficiency.

Or here is another option that works just fine - cut the air line end at a steep angle and position it as in the drawing.