Backyard Aquaponics
A place to discuss aquaponics

Stuart, first part of YouTube video about the air lift of Koivrienden:




And second part:




Another one was about making the air outlet more efficient, so that it will lift the most possible water amount for a given flow and pressure. The principle is based upon using very small bubble sizes to start with. Looking for the link right now and post it when found again.

BTW, my air lift at 40 meter will NOT be used for circulating the system, only to pump up well water into cisterns for storage. From there it will we used for drinking water and water for the AP system. Nitrogen will be no issue. Don't forget that water from the municipal supply is also pressurized, not giving any nitrogen issue for the users.

And this is the link to the website where they talk about the increased efficiency of air lift pumps through sizing of the air bubbles.

http://www.alabdiffusers.com/Airlift.htm

I've seen the link before and I'm pretty sure its been discussed in at least one other thread.

With airlifts they work because the air/water mix in the riser weighs less than the water outside the riser. The lesser density of the fluid mix inside the riser gets pushed up by the external water. What works against this is that the air bubbles are moving up due to weighing less than the surrounding water in riser. This means the the velocity of the bubbles equals their velocity due to buoyancy in water plus the velocity of the water.

Smaller bubbles have a much smaller buoyancy induced velocity so they make for more efficient airlift.

Another way to look at it is that you have two air flows. One is water the second is air. The closer the velocities of the two flows are to each other the more efficient the airlift.

I'm remembering why I stopped looking at airlifts as a primary pumping option.

Smaller bubbles make for a more efficient airlift but require a greater operating pressure. Combined with losses in the compressor makes for an inefficient water pump.

If you look at the table it shows that while the fine bubbles are more efficient the efficiency is still pretty low (<20%).

Where airlifts could claim back some ground is if you also include their ability to transfer gasses into and out of the water. Hard to calculate absolute effciencies but you could relatively easily work out relative efficientcies.

Ie if airlifts move 10,000L/hr and add 500g of O2/hr how does this compare with a dedicated water pump and some other way of aerating the water.

A dedicated water pump can have an efficiency upwards of 70% but if you have to inject a certain amount of air at a certain depth to get a certain level of aeration as well then the efficiency of the airlift at moving water might not count.

This reminds me of a long drawn out discussion about the difference between productivity and efficiency.

... don't go mentioning pumps, aeration, and "efficiency"....in the one sentence...

You'll trigger alerts all over the internet... and tingle spines in Belgium...

You remember.

How could I/we... ever forget...

How critical is the vertical location of the air inlet in the pipe? Just wondering if I put a full length pipe in a 1.2m deep tank and put the airstone at 0.5m depth whether I'd get better water movement than putting the air stone at 1.2 m where it will struggle to make many air bubbles (due to limit of compressor)?

I'm just thinking of ways to ensure circulation and mixing of water between the top and bottom of this deep tank.

Anyone who has actually read the good pumps bad pumps thread knows exactly who you are talking about.

I'm think the discussion we are referring to predates the good pumps/ bad pumps thread.

Its very critical and for most compressors in this situation the deeper the better. Most air pumps compressors used in tanks have a peak efficiency point deeper than the air stone can be placed. For a tiny aquarium airpump used in a AP ft around 1m deep it may be better to have it higher but you would have to do the calc to work it out.

I've always used airlifts with no air stone, just an injection point(fitting) with airline attached to it. Large bubbles rise faster, displacing water very well. If you want more lift, you decrease the diameter of the pipe as you go up. Many times we use them in tank to add circulation and b/c there is no head pressure they work very well.

Is there a reason you're trying to use an airlift instead of an efficient pump?

The bubbles moving up is not what makes an airlift work though. The decreased density of the air/water mix in the airlift gets pushed up together by the denser water on the outside of the airlift. This is why submergence is so important for getting more lift and flow from an airlift.

Straight air injection works and works well but the because the bubbles are moving faster than the water the water ends up slipping past the bubbles decreasing efficiency. The larger the bubbles the worse this gets until you get slug flow (one big bubble) rather than bubble flow up the airlift.

With slug flow it is difficult for the water to slip past the bubble so more water gets pushed up. This is one of the ways that geyser pumps are more efficient at moving water because they almost always generate slug flow. The larger the pipe diameter though the less efficient slug flow becomes more water gets around the slug.

I was thinking that in combining circulation and air pumping in one device, could increase efficiency and hence decrease power consumption. Since I run everything on solar power, any power saved is welcome.
Looking at what you said about running your systems on a 20amp breaker at 110v (I assume) you would use about 2,500watt max. On a daily base that can count up to to 24x2.2Kwh=53Kwh a day.

I'm looking to use max. 1Kw per hour 24/7 for the whole system. Wether that is possible, I'm trying to find out. This amount is of course exclusive the air lift for the well.

For your well, have you looked at a windmill solution? They are incredibly simple.