Backyard Aquaponics
A place to discuss aquaponics

Does anyone know how to calculate how high an air pump can lift water in an air pump lift system?

heres a few links that have useful airlift info

http://aquanic.org/publicat/state/il-in ... irlift.htm
http://home.netcom.com/~larry_l/air_lifts.htm

airlift pumps are very inefficient, both at pumping to any head as at aeration.

I have studied all possible papers on this subject for months now.
here are my conclusions in a nutshell:

on pumping:
very few papers mention flow rates
even less mention at what head these flow rates occur
most of them never ever talk about the power input for the blower,
of those that do mention head, flow and power input, I have calculated that pumping efficiency is rarely above 10 %, more often 5 % or even much less.

for aeration:
while bubble aeration seems to be efficient as such,
it is only efficient when the highest possible air surface is exposed to the water for the longest time possible.
This means very small bubbles: many small bubbles expose exponentially much more surface than their volume equivalent big bubble.
As they are small, they will rise very slowly (which is good for aeration but by definition makes them unsuitable for pumping: they will not raise the water) compared to a volume equivalent big bubble that surges upwards (which is good for pumping as this bubble acts as a piston).
To create such small bubbles, you need special high tech diffusers (expensive).
AND you need big surface, so more or bigger diffusers (expensive).
The smaller the bubbles, the more the diffusers are prone to clogging (less self cleaning potential), so LOTS of maintenance.

To my opinion, airlifts have only two interesting applications:
1. protein removal
2. transport of fragile or vulnerable organisms like larvae, small fry, and live foods like daphnia or artemia (but this can also -and better- be achieved by a siphon)

please someone contradict me. I am eager to learn.

greetings

frank

Some ramblings for you to consider:

I use an airlift pump to 'lift' water from the bottom of my pool to the top. Used this way, the airlift pump is efficient for pumping water (zero head). The air pump I use to drive the airlift pump, in this situation draws 35 Watts. It pumps in excess of 3,000 lph. My water pump also draws 35 Watts, and can pump a maximum of 3,000 lph (zero head). Comparing my water pump to other water pumps I consider it to be quite efficient. In this case the airlift pump is more efficient than the water pump.

Significant aeration occurs by 'turning over' the water, i.e. top to bottom/bottom to top, as air is absorbed at the surface. By 'lifting' the low DO water from the bottom of the pool to the top is effectively providing significant aeration to the total body of the water.

took my time to do some "considering" :

how do you know? you can't measure (nor calculate) the volume at zero head.

Are you sitting down?
following calculation might give you a shock

Let's, for arguments and calculations sake suppose your airlift pump pumps 3000 l/hr at a head of 1 cm.
putting these data in my little excel sheet gives these results:

mylesau airlift
A per hour B per minute C head in m D head in bar C pump effect D input E efficiency
3000 l/hr 50 l/min 0.01 m 0.001 bar 0.00008 kW 0.035 kW 0.2%
B=A/60 (l/min) D=C/10 (bar) C=B*D/600 (kW) E=C/D

let's keep this quiet, shall we?


Of course the above calculation is also valid for your centrifugal pump.
But here the result doesn't shock me: no centrifugal pump is designed for such small head.
It will probably perform much better at 1 or 2 m head or more.
propeller pumps are slowly getting introduced in seawater aquariums (for imitating waves).
To my opinion hey would be a better choice.

Frank

Myles
How do you measure the water being moved by the airlift pump?
Pushing volume of air is dependant on water depth, not like a submersible pump in which pressure, to start with, is equal on both inlet and outlet (for practical situations in AP).

Nothing more scientific than using a large bucket and a timer - this was done fairly roughly at the time, and I will do a better job when it's warm enough to get into the pool - the head was slightly above zero, but the flow was better than 3,000 lph. I measured/compared it with the water pump pumping submersed in the pool at the same head (near zero). It was obvious to me at the time that the airlift pump was outperforming the water pump.


Not sure what your suggesting with this comment? Perhaps its just a statement - I agree...

From my earlier readings on Airlift pumps there can be more going on then most realise - depending on how they are setup they can have Annular Flow, Bubble Flow, Churn Flow or Slug Flow - or any combination of these.

Power usage of my pumps was measured to be 35 Watts, this I know to be correct for both (+/- 1 Watt). The flow was a roughly measured value that closely matched the water pumps specifications and had more value as a comparative test i.e. the airlift pump pumped the same amount of water as the water pump in a shorter time period.

I don't know the air flow of my air pump, I suspect it is somewhere between 50 and 70 lpm at atmospheric pressure. It is putting air into the airlift pump at around 900mm depth. The airlift pump is made simply out of 40mm PVC pipe with an elbow at the top.

Something that my be of interest - I did read a paper on airlift pumps with results showing better performance with a taper which increased on the riser (larger at the top then at the bottom) - this seemed to be opposite of what I would have expected - but there tests were pretty conclusive if I remember correctly, and it did make sense with the change of the type of flow that occurred.

Frank, I think it depends on what you are looking for in efficiency - in this case I want maximum flow for minimum power usage at zero head. Zero head doesn't play well with your calculations

Sorry, guys and girls,
but I am not going to spend more time discussing airlift pumps or airlift aeration unless you come up with some relevant new information
been there, done that enough here and on other forums
So I will try to answer your questions for probably the last time
but please stop challenging me unless you come up with some relevant new information

the results of my -believe me- long and thorough "quest for truth" on this subject are all in my previous post
If you wish to discard my findings, so be it.
up to you.
I gave it my best, posted the results and am now ready to give up the struggle.
because you cannot fight religion.
I cannot see the point of further discussing the pros and cons of either one of two pumps of which I have shown the energy efficiency to be less than 1 %.
0.2 % to be exact and that was allowing for a head of 1 cm.
These pumps belong in the garbage can.

I already stated that in my post to start with
for any pump there is no such thing as zero head
Even if the water surface is only rippled there is head

without head, not a drop of water will flow into your bucket unless you hold it below water level which would be cheating

energy efficiency is energy efficiency.
Period.
you cannot manipulate energy efficiency, you can only divide it like between pumping and aeration (and heat and sound and wear).

While that is true, it does not affect energy:
while pushing the air down further, which SEEMS (perception !!!) harder and harder to do and SEEMS (again perception !!!) less and less efficient, you are in fact converting kinetic energy into potential energy.
this potential energy is reconverted into kinetic energy once the bubbles are released at whatever depth.
except for friction losses caused by the tube (converted into heat, sound and wear) and within the limits of your blower design (if you don't respect this design, more energy will be converted into heat, sound and wear right at the blower -same goes for respecting the design of any water pump), no energy at all is lost by pumping air deep down into the water.

hope this helped to ban religion from science

Frank

It looks like you might be better off using a 3" pipe instead of a 1.5" according to this page
http://www.ca.uky.edu/wkrec/AirliftPumps.htm

Frank, I'm not religious You sound a bit fixed in your thinking, does that mean you have some religion - meant as a joke, please don't take it the wrong way.

My understanding is that centrifugal pumps are not very efficient at low head, piston pumps are typically better - I would suggest that an airlift pump in some instances resembles a piston pump (some aren't - see my previous comment about different flow's within the riser)...

I've provided an example where an airlift pump outperforms a typical low power centrifugal pump of same power usage - you may consider these to be very inefficient pumps - for their purpose, I don't. Find me one that is significantly better in a similar size and I'll be very happy.

One of the few commercially available propeller (axial) pumps that I know of in this flow rate range is the VorTech Propeller Pump. It would certainly be the choice for this situation (as you have previously mentioned). However there are a few issues. It's damned expensive ($690 for me). It has a propeller that would cause me unending problems with fowling etc. Its efficiency is less than 2%, probably closer to 1% if mounted in a tube to perform the same task as I use my airlift pump for - it is sold as being one of the most efficient pumps available on the market - should it be put in the garbage too, due to its low efficiency?

A point to note, I have not made any successful attempt to make my airlift pump the most efficient it can be - it is quite possible that using an air pump 1/2 as powerful may result in a similar flow...or splitting the flow may result in twice the flow.

I think it should be noted that the appropriate pump for the job is often more important than absolute efficiency. From past reading, I believe Mylesau's air lift pump is doing a job that few regular water pumps would be suited to. It is sucking water/leaves/etc off the bottom of the pool, lifting to the surface and catching the debris in a net while circulating water to the surface. The aeration is not happening much from the bubbles in the lift tube, the aeration is happening as he said by bringing bottom water to the surface. The biggest point here is that the air lift is not getting clogged by lifting the leaves and debris where a regular pump would need more regular trap cleaning to keep from damaging it. If the debris net on Myles airlift gets too full, it won't damage anything.

Now to move water from a fish tank to the grow beds, air lift may or may not work very well depending on the situation.

one more exercise just for the fun of it:

(hadn't seen this paper, so I owe it to myself to check)
ca.uky
per hour per minute head in m head in bar pump effect input efficiency
3107 l/min 0.025 m 0.003 bar 0.01295 kW 0.750 kW 1.7%
conclusive, isn't it?

good try, mylesau, to make my expression backfire on me
but it doesn't work that way:
give me any paper that contradicts me and I will change my mind (after checking, of course )
I am not the one that keeps defending pumps/systems with energy efficiencies of less than say 5% (I'm in a generous mood)
I'm trying to correct this wrong assumption.
But I am a realist: while the ancient Greeks already knew that the earth was round, it took to beyond the middle ages to get this knowledge accepted.
So I have a few more years to go.
Please accept that this prospect is making me weary.
Luckily I am not the only preacher around:
http://www.advancedaquarist.com/issues/ ... review.htm

no you haven't, you have compared one type of pump to another, the second one NOT designed for the purpose.
so your comparison is irrelevant or, to say the least, unfair.
The Vortech propeller pump is outrageously expensive.
A propeller (like used in model boats) typically costs less than $10 (and that is a high tech carbon reinforced one). Replace the impeller by a propeller as suggested in the above link and you will come a long way.
And the Vortech propeller pump is absolutely inefficient (as you seem to have calculated, thanks), so absolutely fit for the garbage can (more efficient not to buy it ):
Vor Tech
per hour per minute head in m head in bar pump effect input efficiency
11370 l/hr 190 l/min 0.01 m 0.001 bar 0.00032 kW 0.035 kW 0.9%



from TCLynx:

please stop wriggling around and speculating
maybe and might are irrelevant until proven

Now that, TCLynx, is a valuable argument.
Too bad I have already countered it: a siphon will achieve the same result

All keep on questioning your religion, you are on the right track

Frank

I guess its a case of horses for courses.
Some scenerio`s might favour the airlift, independant tanks for different species, water parameters or whatever for example. A single regen blower/distribution manifold would be less initial outlay than a large number of seperate pumps.

Another unseen advantage with the blower is if you buried a few hundred metres of tube in the ground you could reroute the intake (via a diff stat) to take advantage of low ground temps to help cool the air going to the tanks. In winter it could temper the cold intake air somewhat

Now Frank, I think it is you that is wriggling - I put up a challenge - find me a significantly more efficient pump for my purpose!

Power usage must be 35 Watts or less and is required to provide a continuous flow of at least 3,000 lph - if you want to pump to some significant head, that's fine, I can gravity feed back into the pool but I don't have space for any large holding tanks and do not want to increase the volume of water requiring filtration etc.

I can not use a siphon with my pool in the ground and I want to recirculate the water not just move it to another location!!!