Backyard Aquaponics
A place to discuss aquaponics

Yav; if it was some cute scantily dressed female doing the presentation (with occasional naughty bits) I probably wouldn't have abused my games monitor (futile but a way of relieving my annoyance).
I would have let the slow, DAF explanation of basic physics and the irritating repetitive manner in which it was presented slide over; (and turned the sound off).

his discussion is a bit like watching a tennis game.

Hey Joel, this is Steve I see you put up the link to part 2 which has more technical stuff than part one. I hope there is something in there that can help someone, if not I meant well. Thank you for considering the idea! Hope I can find something that will be more helpful next time. Regards, Steve

Careful they are watching

I ran across this forum while searching some internet links. Airlifts are my thing.

Several of the threads argue efficiency. One offered data without offering the actual equation(s).

How are you defining efficiency? Cost, mechanical, energy, design, materials?

Airlifts performance is affected by many variables -- flow rates (air and water), pipe diameters, submergence, injection depth, air diffuser vs. direct, design (cylindrical vs. rectangular).

For any given airlift, flow rate will decline as lift height increases. Maximum flow will be achieved at 0.0 lift (100% submergence).

Both air and water flow resistance are determined by cross-sectional area of the conduit and flow rate of the fluid (air and water). Greater resistance equals lower flow. The closer you get to laminar flow the better.

Small bubble size from a diffuser adds more oxygen because of bubble size (higher surface area to volume ratio). Diffusers have much higer resistance to air flow. Remember oxygen content of our atmosphere is 20%. Rate of exchange is related to oxygen concentration in the water being pumped. The smaller the pore in an air injector the more prone it will be to bio-fouling and calcification.

Perhaps TMI for my second post here.

I have designed and built airlifts for over 2 decades. A few years back, I discovered Rectangular Airlifts. My interest in airlifts is to circulate exceptionally large volumes of water as quickly as possible using power units in the 1.0-2.5 hp range (0.75-1.88 kW).

From my experience, airlift pumps are capable of moving a large volume of water at low static pressure and 100% submergence in a relatively short period of time. Of course, as you increase lift height, volume discharge falls substantially.

At zero head (100% submergence) and an injection (static) pressure in the 28-32 inch H2O range, it would appear that rectangular airlifts are capable of circulating 2000-2400 gpm (456000-547200 Lph) per hp using Gast 1.0-2.5 hp “regenerative” blowers. At a cost of US $0.113/kW-hour, that would be $2.03/hp-day ($0.0008 to $0.001 per gpm daily).

Seriously, if somebody can direct me to 1.0-2.5 hp water pumps that can pump 2000-2400 gpm continuosly at zero head for an affordable unit price, I am very much interested in discovering that commercial supplier/retailer.

Basic Rectangular Airlift:

http://www2.ca.uky.edu/wkrec/RectangularAirliftPump_11_12.htm

I don't think we're argueing that they don't work. It's the lifting ability that makes it fall short for many of our purposes. My beds are 700cm off the ground, and from 2 meters away - 15 meters away. The 40w pump I have pushes 8000Lph (less with the curve, but enough for my purpose). I'm happy with that. However, if there is a way to make it work with an airlift, for less energy, I'm all ears, because I'd happily use the benefit from the extra oxygenation.

I see something like a mineralisation tank working very nicely with an air-lift pump, or maybe a natural pool

Best I've got is 116L/sec drawing 1.5kW @ 0.3m head.

No question, airlift pumps are not the ideal choice for lifting water. However, they are particularly effective for circulating water at zero head.

The designs on slides 37 and 39 in the slide show at the following link look like they could work well for recirculating tank and/or raceway components (5.2 MB, file downloads a bit slow).

http://www2.ca.uky.edu/wkrec/Rectangula ... pWurts.pdf

How are they/you calculating the waterflow with the pump?

In the open water, it looks like it'd be very hard to calculate with the amount of bubbles going through it, they'd take up a large volume of the water. And I'm pretty sure that blower would use a very large chunk of electricity.

Are there any aquaculture places using them?

Except that raceways suck in most circumstances for aquaculture.

Airlifts can and do have their place but its limited due to their inability to do actual work (ie lift).

Having said that a new study on different aeration methods is over due due to advances in airflit design and technology (rectangular airlifts being one example). The old research demonstrated that paddle wheels where superior in ponds but those studies didn't compare rectangular airlifts or many or the micro pore diffusers and other improvements in compressed air aeration.

I will try to answer both posts briefly (?).

My designs are for circulating large volumes of water in relatively large impoundments. Little doubt in my mind that my designs will accomplish my objectives. I have not built the critical component that works in conjunction with the rectangular airlift. To do so, would prevent my ability to patent at a later date by making it publicly known. I learned a costly lesson about patents on another project.

I built a 1.0 hp rectangular airlift to see if it worked. I observed high volume output but had neither the resources nor the equipment to test it. I'm closing quickly on retirement. So most of my projects are design oriented now.

The bubbles dissipate in a very short distance,1.5-2.0 feet. Measuring output flow would be fairly easy -- a shallow flume of known dimensions and enough length attached to the outflow, and a good flow-meter to measure water velocity.

The article in the link posted above indicated max flow potential was determined using Air Pump software developed at Cornell Univ. (Reinneman and Timmons, 1988). I purchased two editions of Timmons et. al. RAS book. A CD containing the 1988 Air Pump software came with both. Using that software, I calculated potential flow rates (2000-2400 gpm) consistent with the article linked. Based on my observations of an operating unit, I am convinced the output flows are likely with a properly constructed rectangular airlift.

Reinneman built a lignocellulosic RAS concept that used "airlift weirs" -- essentially rectangular airlifts -- in the biofilter and found 10% better performance than anticipated. The project was to demonstrate the efficiency possible using airlifts.

Look up the airlift work of S. Gudipati and Dr. Ron Malone on the internet, student and engineering professor, respectively, at LSU. Fairly technical stuff.

Ron Malone has designed several large scale, commercial RAS systems for tilapia production using raceways powered by airlift pumps. They have been built, are currently operating and look most impressive. I find Dr. Malone's work to be highly credible and scientifically substantiated.

Airlifts are fairly effective for CO2 removal also. I believe the lack of turbulence with very fine bubble streams (micor-pore diffusers) are inneffective for removing CO2.

Regarding micro-pore diffusers, small bubbles allow higher oxygen transfer because of their higher surface area to volume ratios. However, the rate of transfer is determined by concentration of oxygen in the water to be pumped. Also, oxygen tranfer is limited by the 20% atmospheric oxygen content. Small pores bio-foul and calicify easily, reducing or blocking air flow.

For compressed air systems how much energy is used to compress the air.

I would have to write a thesis to discuss any of this in depth. I have a very broad scientific education but am just another shade-tree engineer.

It's time for bed and I have been typing this response very quickly. So I'm sure there are many typos included. Hopefully none of them are critical to the discussion.

BTW the Air Pump 2 software available free on-line is flawed and does not accept airlift dimensions properly.

As I said there is a need for further research in this area as direct comparisons have not been made beween paddles wheel aerators and the new generation of air lifts and diffuses.


Yep easy to do. There are a range of meters that measure flow in channels wouldn't be hard to do at all.


I'm vaguely familiar with this work so I'll have to read it again. From memory it was a good design for RAS and possibly AP systems where the solids are removed but not so good for AP systems where there is no need for a dedicated biofilter since there ins't a biofilter within which to install the box airlifts.


If you have two copies of Timmons et. al. you would be aware of the issues with raceways. Yes they can work but they are not ideal.


Why would there be any difference? Gas transfer would be influenced by relative concentrations and surface area.


Which is why aerators have traditionally been less efficient than paddle wheel aerators.

Stuart,

Thought you might be interested. Basically, airlift weirs are rectangular airlifts.

http://www.ecw.org/sites/default/files/205-1.pdf

"1). The theoretical model under-predicted the pumping capacity by about 10%, probably because of the
reduced wall friction in the weirs as compared to the 20-tube model. The model can thus be used with
confidence in the design of aquaculture facilities."

From page 10.

Article by L. Gasner (1974):

Gasner, L. L. (1974), Development and application of the thin channel rectangular air lift mass transfer reactor to fermentation and waste-water treatment systems. Biotechnol. Bioeng., 16: 1179–1195. doi: 10.1002/bit.260160904

†
Presented at the 166th National Meeting of the American Chemical Society, Chicago, Illinois, August 26–31, 1973.