Backyard Aquaponics
A place to discuss aquaponics

Now to address some actual points regarding Franks "High gain passive oxygenator"...

I'm uncertain as to the actual "scale".... the size of the proposed passive oxygenator... but have some thoughts...

From what I gather ... the water flows over the top corrugated panel and "sucks" air as it passes over the inbuilt "flutes"....

Because Frank says... "it slows" the water.... this may be true... but given the design drawing the amount the water may be slowed, would seem minimal, given the short "height" of the fall...

Subsequent corrugated "layers" seem superfulous in terms of the length as drawn... if the water is merely cascading from each layer above... as it's only the "length" of the corrugated section that receives any flow from that above it...

And because... each layer can only achieve the same amount of "aeration" through the "slowing" of the water and venturi affect anyway... due to the same height involved..

Indeed... I wonder as to whether the corrugations actually acheive any real benefit... wouldn't the water flow primarily down the downward corrugation... meaning that the upward facing corrugations are essentially redundant...??

My other concern Frank, is that you have based your design upon discussions of Low heaqd Oxygenators (LHO), found within the paper http://aquanic.org/publicat/state/il-in ... pure.htm... that you reference in one of your spreadsheets...

IMO, if this is the case, then you have missed the funamental point of the paper... and your design is flawed... and inefficeint to the tune of approx <80%...

The paper is a disucssion of of such designs... in a totally sealed oxygen injection system.... using pure oxygen.... not normal air, that only contains 20% oxygen...


I can only assume this to be the case Frank.. as you have not indicated otherwise in your drawing.... and describe the device as "a passive" oxygenator....

So your design will only produce 1/5 of the oxygenation in comparison to the desin mentioned in the paper...

And ... because the volume of air being sucked throught the venturi "displaces the volume of water..." ... it is in fact designed with the various "inefficiencies" you yourself have highlighted in regard to "venturis"....

I'm at a loss to understand just what you're trying to acheive Frank....

The goals of an AP system are to ...

acheive filtration/conversion of ammonia waste...
acheive "mineralisation" and uptake of trace elements from solids materials
reduce BOD from suspended solids material
filter "fine" pariticulate matter from suspension
aerate water returning to the fish tank to a satisfactory level...

All of which can be acheived in an AP system very simply.... with two pieces of "low cost" equipment..... a "flood & drain" growbed..... and a venturi or passive means of aeration incorporated into the water flow reutrning to the fish tank/sump...

There is no need for a "solids" skimmer/remover.... foam fractionator.... external fluidised filtration device... settling tank... direct oxygen injection system... etc etc...

All of which are necessary components of RAS aquaculture systems.... because they need to deal with the processes and materials.... which an AP growbed deals with as a matter of design.....in a single unit....

Aint AP grand... in it's simplicity.....

[quote][I have doubts on how much water volume is lost in a venturi.
/quote] My experience has been that flow is significantly reduced. It wil depend on the venturi design, but the more effective the venturi, the more loss of flow there will be. Just put your finger over the air hole and you will notice the flow increase substantialy.

Having said this - I stand by my original view that venturis are great and do have a place in AP.

On a more positive note Frank... I would do several things to improve the efficiency of your "passive oxygenator"....

Turn the "corrugations" 90 degrees... to maximise the disturbance of the "laminar" flow...

Expose the corrugated panels to the same surface area of flow...

Drill holes through the downward corrugations to allow more water to be exposed and aerated, than that which might occur through the venturi affect when it falls from one panel to the next...

Seperate the corrugated panels by a greater distance.... speeding up the water as it falls from one panel to the next, providing greater exposure to both air as it falls and to any venturi affect... and any supplemntary gains that may occur as the water "splashes" from one panel to the next...

Why.... well here's some data for you Frank.... from Ahmed-Boyd (I'll find the exact paper if required)



And heres some examples of an aeration system employed by Koi keepers... that employs all of the above gravity aeration methods....

And works as an extremely efficient bio-filter as well .... known as a "Bakki Shower" ...

Basically they're a "trickle" filter incorporating baffles "splash boards, or corrugations, bars", lattice (drilled holes) and weirs (laminar flow)..... combined with media for filtration... essentially "fluidised" bead filter.... ....

They can also have a "cooling" affect... they do suffer some evaporative and wind blown dispersal losses...

No, Sleepe, I have not
and I admit this to be a possible weak point, so I should have mentioned it
I will in the future, as I like to point out both the pros and the cons of a system.

To me, where I live, water loss (by evaporation) is not important: we have enough rain
Still I wish I had a way of calculating it. Who can help me here?

Temperature losses are probably easier to calculate, and they are important to me
so I might decide to paint the sunny side black and insulate bottom and back side
and to cover up the holes where I have no plants (if any).

I can agree with that, Dufflight, at least partially:
As long as there is no pressure build up in your piping, the Venturi at the outflow into the fish tank is not going to cause energy loss.
So that would also be a passive way to aerate the water, and in that case it will be both effective and efficient.
I will add it to my list.
but that doesn't seem the case where you describe your system, Dufflight:

means you will have pressure buildup.
TMHO in these circumstances a Venturi will more lessen than enhance aeration.
I would consider that a bad and unproductive investment.
Not only for aeration:
recirculating more water will also reduce relative fish density, will enhance fast solids removal, will make for happier fish.

as for cost effectiveness, that would have to be calculated setup by setup.
All factors should be taken into account here: cost of materials, complexity of construction (which are one offs),... but also temperature and water loss (thanks, Sleepe) on the negative side (which come back yearly) and energy needs reduction (i.e. solar panels and batteries, one offs), reduced energy consumption and extra space for plants (which come back yearly) on the positive side.

what I write is not a belief, Rupe, but a well thought of and amply argumented conclusion, that stays open for corrections.
I never assume things and stay critical to myself. I have been wrong in the past on lots of subjects and am always eager to learn.

wrong, Rupe: I have never suggested "by sheer flow rate and turnover", on the contrary always stated that good design was a necessity

thanks, Rupert, so you accept my reasoning.
but you reject the conclusion without argumentation why you do so.

why always the manipulation of the word "effective"?
effective means it has effect
I don't deny inefficient systems to have effect.
Especially not if only one effect is aimed at.
but that only shows that the word effective should always be accompanied by a description: i.e. effective at aeration
effective at aeration is not the same as efficient at aeration.
Yet that is constantly suggested.
isn't efficiency more important?

wherever have I written that water should be lifted to higher levels, Mylesau?
Head should be kept as low as possible. I have always emphasized that.

my statements are no more blanket than yours, Joel
quite the contrary, they are always represented as my proper conclusions and always supported by argumentation.
my motivation to post my ideas is to continue learning.
and to combat assumptions and rusted beliefs.
Both Sleepe and Dufflight have added to my knowledge in this discussion: temperature and evaporation should be considered and a Venturi can be a passive way of aeration.
You have now too: you bring up the argument of noise.
I agree that has to be considered too.
it is up to the final owner to outweigh all these arguments, not to you nor to me.
if energy efficiency is important and takes preference, I invite anybody to follow my threads as that is my main concern.
If anybody does not think that important, fine with me.
I have no problem with agreeing to disagree.
You don't mind wasting energy, I do.
I have argumented why I think pressurized Venturi's do not add any oxygen
yet you "blanket" state that they all do.
no counter argumentation at all

neither am I saying that nobody is allowed to use them, Joel
everybody does as he wishes.
I am merely posting my findings.
Just like you I have the right to defend them.
Just like you I have the right to express my priorities.
Let it be clear that effect is not good enough for me, but efficiency, at effect.
Just like you and anybody else I have the right to express my thoughts wherever any subject comes up.
I try to do so in a friendly way.
sometimes I fail. That is never intended.
like in the sentence:

I should have inserted TMHO.
but as this is just one sentence lifted out of a post where I clearly stated this to be my opinion, I thought this to be unnecessary
I was wrong. I apologize if that was not clear enough.
I am human.

apologies also for the length of this post
but I am beginning to feel like David against Goliath.

frank

please everybody, let's keep this discussion simple:

I have explained why I am convinced Venturi's are not efficient at aeration, even detrimental to it
I have also explained that to me efficiency is more important than effect
TMHO the effect is purely visual and our eyes might fool us
I am convinced they do

please explain to me why you think that Venturi's could be efficient (not only visually effective)

Rupert, I appreciate your remarks on my design of the passive aerator, even agree with some of them
but this thread is about Venturi's, don't you think?

frank

Sorry Frank... but the way I've read other (numerous) posts, it appeared that you were firmly of the belief that aeration could be acheived merely by pumping water at high flow rates....



Again, sorry Frank... while I agree, and seems self evident that any air injected by a "venturi" effect will displace an actual "volume of water".....

You haven't actually provided any factual evidence or measurement to support this at all... it is your belief, possibly well thought out... and probably correct (self evident)...

But not actually supported by reference or data... just commonsense perhaps...



I concur with what you postulate Frank... in regard to the air replacing a "volume" of water... but yes ... do reject your conclusion that venturis have not place because of that...

And then did advance "argumentation" as to why.... part of which was to say that "in the end"... levels of oxygenation were acheivable... even if it required a certain level of water volume turnover each day... possible even fractionably more because of the "venturi" displacement...

But, that in a recirculating system such as AP... either constantly pumped, or interval pump.... that this wasn't a problem... that sufficient capcity was available....even if at some level of efficiency....

Therefore the means employed (venturi) was "effective" in acheiving the aims and goals (clearly stated).... even if not totally "efficient" by nature of a components design...

There was no intended or inferred "manipulation" of the word "effective".... it was purposably chosen to differentitate from "efficient"...

Given your dislike of venturi induction of aeration and inefficiencies and ...



Why have you designed your "passive" oxygenator to not only incorporate such an "inefficient" methology.... but to rely totally on it Frank?????

And have done so .... IMHO.... in the most inefficent way....

Google is our "friend".... but references and papers should always be read in their entirity, cross referenced and corrolated.... not "cherry-picked" to substantiate an already held position or "belief"...

And I will post later concerning your "low head" design... which I believe has flaws... none the least of which, as Steem points out, is heat loss/gain...

Yes it is.... but you have populated many threads with your theories regarding "venturis" and "aeration"...

Thus I suggested that the thread be renamed and discussion be directed to a single thread...

Not only to discuss the "issue" directly, but to discuss your proposed designs as well as your theories...

Either that, or that you should start a thread of your own ... for these very purposes...

I believe you responded by saying.... you were to busy.... or that you weren't prepared to do so, because you hadn't/haven't actually completed construction/testing your beleifs and theories...

It has been suggested by members that we would like to see you do so Frank... and report the results... successes and failures....

Almost unanimously, everyone else is saying that the simplicity of aeration by growbeds, venturi and other gravity aeration devices as they employ them.... works just fine...

Most have even agreed that .... they may not be totally "efficient" as such.... but... they work....

Build it, test it, document it Frank.... I have doubts as to some of your design proposals... for reasons discussed by many over the last few years...

But seriously would welcome, and am open to any improvements that can be made/acheived...

But sorry mate... until you can show me (and others) what can be done differently... and works....

Then they are your "beliefs", "theories" and opinions.... perfectly valid.... but not necessarily "facts"...

Look at you diagram Frank...Is there not a head difference between the inlet and outlet of your so called "passive" oxygenator...how did the water get there - perhaps the purple frog carried it there?

Can you please show all of us how it is better than a Venturi - you state that you have done that, but as usual you haven't - it is your perception, which you so love accusing everyone else of having - how about showing how you calculated this - maths, engineering, fluid dynamics, real data... - you just make statements and want everyone else to accept them - it ain't never going to happen.

One of the reasons I asked for scale Myles.... there is an obvious head requirement to be pumped... from where ever....??



Actually Myles.... he appears to be, as much as he claims it is inefficeint... to be using a "venturi" affect... the whole design is based upon it!!

I already have pressure in the pipes. Letting some out is helping so I don't think letting a little less would be that much of a problem. Or just put in 2 Venturi's instead.
This is only until I have more GB's online.

Ohhh this looks like fun. So many points to make but I'll restict myself to a two.

In Australia water loss from a system is in most cases going to be a bigger issue than electricity effciency. We have just had the driest begining to spring on record (since 1914) so it looks like we are heading into another year of drought. Those trickle towers look like they would create a relatively large water loss due to evaporation. Any design which had a similar loss would be completely unacceptable for systems in areas where water is scarce.

Having said that air bubbles moving through water would be likely to collect waper vapour within them and when they burst at the surface this vapour would be lost to the system. Whether that would be as bad as a trickle system that was shielded from breezes or not I don't know. If it wasn't sheilded from a cross draught (as depicted above) then the evaporation would significant.

Second point. Are you aware Frank of the gradle to grave comparison between older style 4WD vehicles and modern hybrid cars. I heard about it on the ABC (equivilent to the BBC) and the conlcusion reached by the author was that the big, heavy, petrol guzzling 4WD vehicles were the more environmentally friendly. What it came down to was that any saving made by something such as a Prius were completely blown out of the water by all the energy that was involved in making the hybrid vehicle. The fact that is that projected life span of a mostly plastic hybrid vs. a mostly steel 4WD is so short and the energy required to make the hybrid so large vs that of the simple 4WD.

So your design of aerator or pump had better be massively more efficient than the simple to construct, operate, maintain airlift pump or venturi. Every extra cm3 of plastic or steel involved in the construction is going to horible things for its energy effciency if you consider energy effciency from the position of cradle to grave rather than just that of operation.

Frank

You keep us from becoming complacent; that is a good thing

I think that some of this nearly heated argument is due to lack of clear premises being stated.

Frank is primarily interested in energy efficiency. I know that venturis can greatly decrease the flow of water - for several reasons - 1- they create back pressure in the constriction, 2 - they mix air into the flow, 3- nearly all have to push the air under the water, 4- I had an aquarium power head that lost about 25% of its water flow when the venturi was enabled.

Frank's cascading oxygenator would be scalable, but would have different efficiencies, depending on head, pump speed, things to disturb the laminar flow of the water, buildup of deposits on the tiles, relative humidity, etc.

There are other factors in other people's designs. From my view, minmal moving parts, single pump, and simplicity are bigger factors than energy efficiency. I have a swimming pool that pumps 4200 gallons per hour, (16,000 lph). The small 300gph pond pump I''m planning on using for my AP is not going to be noticeable on my power bill. It would be much more noticeable if I had to take more area for my AP system.

Another issue is the type of pump available. If you have an extremely efficient pump well pump, then your design would be very different than an impeller pump. Another issue is the materials availability and cost. If I have to fly a turn-key system from Joel's shop to the US, it's going to take decades to recoup the energy spent on Jet fuel versus the difference in a 20 watt versus 40 watt pump.

Another issue is the aesthetic issues. May not be the same issue for all people. If I have my system on a 500-acre farm, I'm not too worried with how it sounds or looks. If, on the other hand, I have neighbors who would complain about looks, sounds, smells, or whatever - and a neighborhood association or municipality that would jump at any chance to shut anything down that is out of the norm, then that becomes a larger issue.

There are areas where one resource or another is plentiful or scarce. In Australia, water efficiency is very high on the list, electricity is more plentiful. In Paris, they have plentiful electricity, but aesthetics would be paramount. Frank has power consumption as a prime consideration.

Another factor is based on economies of scale. I have a family of 8. Others have only themselves. Others are working on commercial operations.

There's also a difference in what people are wanting to get out of the system. There was someone who was vegan, and had the fish only to feed the plants. There are those who are interested in veggies, only as condiments for their fish.

There's an old saying that "All generalities are false - including this one." Almost every time we try painting with a broad brush, we're going to miss the mark in one way or other.

Is my AP design going to have a venturi in it? Possibly. Will I lose water flow? Definitely. I had a power head that lost 25% of its water flow volume when you turned on the venturi. Is this thread useful? Absolutely. I will likely use this venturi design in my swimming pool ozoneator design. Should this design be used for all AP designs? No. Each person in BYAP is working towards a specific goal.

People need to take the information here, and see how it compares to what they're doing, and if it has a place in their system. I have redesigned my system multiple times, and each time, there are tradeoffs. After running it for a couple years, would I do it differently? Probably.

I don't think many of us disagree with all of Franks points, indeed he has some good ones. It is more the generalisations and the all encompassing statements like "venturis have no place in AP" that are raising hackles.