Skimmer 2 minute dwell time. Anyone have any proof of this?

[mr.wilson]

<a href=showthread.php?s=&postid=8750580#post8750580 target=_blank>Originally posted</a> by JC VT
Hi Mr. Wilson,

Do you have a copy of the Rubin paper in pdf format? I'd love to take a gander.

Also, can you elaborate on "these laws don't apply to downdraft skimming"?

No I don't have the paper, just the reference to it from Stephen Spottes "Fish & Invertebrate Culture".

What I meant by the differentiation in skimming laws is that most skimmers use air to bombard water. As such, certain laws dictate efficiency. Mind you, one parameter may be respected at the cost of losing another.

Downdraft skimmers fractionate water to such an extent, that there is more air than water in the reaction chamber. This process leads to immediate migration of hydrophobic molecules and their hitchhikers. The rapid pace at which it's carried out allows for POC export before the heavier particles get a chance to settle back into the lower reaction chamber. Aspirated skimming methods like air diffusers, venturis, and pin/needle wheels rely on dry, stable foam to stop gravity from returning heavier particles (POC) back to the reaction chamber.

Protein skimmer design, as well as bioogical filtration like wet/dry towers, is borrowed directly from the designs and research used in waste water treatment, as we don't have a research budget. Degassers (air strippers) are used to remove gasses and a variety of chemical compounds (VOC's) in raw waste water (see Henrys law). There are different methods of accomplishing this. Some use fine sprayers similar to Aqua C technology, while others use a shallow tray like this one that can be seen in replicated in Bubble King design. http://www.neepsystems.com/Pages/ASTechno.php

 

[JC VT]

Downdraft skimmers fractionate water to such an extent, that there is more air than water in the reaction chamber. This process leads to immediate migration of hydrophobic molecules and their hitchhikers. The rapid pace at which it's carried out allows for POC export before the heavier particles get a chance to settle back into the lower reaction chamber.

Mr Wilson,

Do you believe this holds true of beckett type skimmers as well? That the becketts fractionate water to the extent that it leads to immediate migration of hydrophobic molecules and their hitchhikers at/after the beckett?

 

[mr.wilson]

<a href=showthread.php?s=&postid=8754495#post8754495 target=_blank>Originally posted</a> by JC VT
Downdraft skimmers fractionate water to such an extent, that there is more air than water in the reaction chamber. This process leads to immediate migration of hydrophobic molecules and their hitchhikers. The rapid pace at which it's carried out allows for POC export before the heavier particles get a chance to settle back into the lower reaction chamber.

Mr Wilson,

Do you believe this holds true of beckett type skimmers as well? That the becketts fractionate water to the extent that it leads to immediate migration of hydrophobic molecules and their hitchhikers at/after the beckett?

Yes, but to a lesser extent. The becketts I use have a large contact chamber, so anything that was separated as air and water mixed, are likely "shaken off" by then. If the plumbing was transparent, I would better understand where the migration occurs.

I have a few ETSS skimmers and they appear to have more function in the bioballs than in the riser tube.

The ridiculously long riser on Beckett skimmers, illustrates that it's a completely different methodology, from needle wheels. My beckett riser is about 2' while my needle wheel is about 8". The fact that oils or salinity changes can cease foam development, also supports that downdraft skimmers of any type, are a completely different beast from needle wheel/venturis/air driven technology.

 

[JC VT]

Mr Wilson,

The becketts I use have a large contact chamber, so anything that was separated as air and water mixed, are likely "shaken off" by then. If the plumbing was transparent, I would better understand where the migration occurs.

How might you come to the conclusion that "anything that was separated" would be shaken off?


The ridiculously long riser on Beckett skimmers, illustrates that it's a completely different methodology, from needle wheels. My beckett riser is about 2' while my needle wheel is about 8".

And in fact, "ridiculous long risers" are not necessarily standard on beckett skimmers as seen here :

http://www.precisionmarine.com/html/b3_hires.html

 

[jdieck]

<a href=showthread.php?s=&postid=8756096#post8756096 target=_blank>Originally posted</a> by mr.wilson

I have a few ETSS skimmers and they appear to have more function in the bioballs than in the riser tube.

Yes, the air water interchange happens at the bioball column, the separation starts at the bottom box with the baffle inside and the water outlet from the bottom of the box . Their raisers are just part of the foam separation process.

 

[mr.wilson]

My take on dowdraft skimmers is that they have a quick contact time and comparatively less stable (wet) foam. The extra large riser tube (both wide and tall) is needed to allow wet bubbles to merge into drier, more stable bubbles.

If the riser tube was any shorter on my MRC Beckett, it would act as a water change system.

It skims quite a bit, but the skimmate isn't thick or green. I think the mud I clean out of the neck has more "bad stuff" in it.

I also notice that my needlewheel skimmate smells much worse. I almost gag when I dump it. I would attribute this to a greater amount of bacteria attached to the POC.

Overall, none of these technologies is better or worse than the other, just different.

 

[JC VT]

<a href=showthread.php?s=&postid=8761097#post8761097 target=_blank>Originally posted</a> by mr.wilson
My take on dowdraft skimmers is that they have a quick contact time and comparatively less stable (wet) foam. The extra large riser tube (both wide and tall) is needed to allow wet bubbles to merge into drier, more stable bubbles.

If the riser tube was any shorter on my MRC Beckett, it would act as a water change system.

It skims quite a bit, but the skimmate isn't thick or green. I think the mud I clean out of the neck has more "bad stuff" in it.

I also notice that my needlewheel skimmate smells much worse. I almost gag when I dump it. I would attribute this to a greater amount of bacteria attached to the POC.

Overall, none of these technologies is better or worse than the other, just different.

Hello Mr. Wilson

To quote our beloved chem guy RHF Re: Wet skimming:

For this reason, the most effective skimming, in terms of total organic removal, comes from removing somewhat wet foam, rather than waiting for this same wet foam to drain prior to removal. The primary difference between wet foam, and drained dry foam, is that additional water and some organics have drained away.

 

[JC VT]

so anything that was separated as air and water mixed, are likely "shaken off" by then.

Could you elaborate on this statement?

 

[mr.wilson]

What I meant bu the "skaking off" comment, was that semi-hydrophobic, and weakly attached hydrophobic molecules are dislodged if they experience excessive turbulence. POC hitchhikers would fall into this category as well, as they don't have a strong bond with the bubble, or attached molecule for that matter.

You can "shake-off" attached molecules through agitation, but you can't "shake-on" molecules through the process. They must attach at the non-polarized (hydrophobic) end as contact is made. The polarized (hydrophilic) end of the molecules still have a desire to be waterborne.

The rapid flow of water in a downdraft skimmer causes considerable turbulence compared to a slower flowing needlewheel (based on throughput and path). Downdraft skimmers IMO have the majority of the surfactants migrate to the air/water interface in the downdraft tube, during fractionation. They have a second chance to migrate in the riser tube as the wet bubbles pop and merge. This is why the riser tube in downdraft skimmers is comparitively large, while the reaction chamber is comparitively small.

I have an ETSS 750 Evolution, that has 15 bioballs in the downdraft column. The reaction chamber below is very small, and the throughput is a quick 1200 GPH. The air/water interface in the downdraft column is far greater than that in the reaction chamber. It appears that the reaction chamber has little to do with surfactant migration, as the reaction time and space is limited, while the fractionated water traveling through the bioballs have a viscous, stable appearance.

Once again, my take on downdraft skimmers is that they work more on the bubble popping principal (air stripping) than the bubble attachment theory. Bubble popping being, the action whereby, the water is stripped away from the molecules, rather than the molecules being separated from the water. It's the same process as salt creep and airborne phosphate & nitrate off-gassing (air stripping/degassing).

In summary (with a big IMO), I feel that downdraft skimmers are most efficient during fractionation at the beginning of the process, and merging (in the riser tube) at the end of the journey. The middle part in the "reaction chamber" doesn't obey the rules set forth for air-driven, venturi, or pin/needle wheel methods, and therefore isn't where the magic happens.

 

[sherm71tank]

I did a little test a while back. (No it isn't fool proof) I took my DAS EX-2 skimmer and my Austin Oceans 2000 skimmer, powered by a PCX-40 and ran them side by side in the same sump. Before adding the AO the DAS had been running for several months on the system (a 90 gallon BB mixed reef). I used a MJ1200 for the feed pump on the DAS. Interesting thing happened. After about a week the DAS EX-2 stopped producing skimmate, and I mean stopped. I was kinda bummed because the DAS used less than half the electricity. Hmmm!

 

[geoxman]

I remember this thread from a while back.

those Barr Aquatic skimmers are some of the nicest built skimmers I have ever seen!

It is interesting that it shut the DAS down. I have seen some of the larger ETSS skimmers shut down equivalent size NW skimmers. I wonder if it is because it is processing so much more water via the larger pump??

 

[sherm71tank]

I haven't given up on the NW skimmers yet. I have an Octopus Pro 250 on the way. I hope it does better than the DAS. The proof is in the skimmate!

 

[sherm71tank]

<a href=showthread.php?s=&postid=11982768#post11982768 target=_blank>Originally posted</a> by geoxman
I remember this thread from a while back.

those Barr Aquatic skimmers are some of the nicest built skimmers I have ever seen!

It is interesting that it shut the DAS down. I have seen some of the larger ETSS skimmers shut down equivalent size NW skimmers. I wonder if it is because it is processing so much more water via the larger pump??

IMO, moving alot of water AND alot of air through the skimmer is more important than just tons of air and slow water flow. IMO and IME the wastes we are trying to extract simply don't need long dwell times. I don't have any scientific papers to back it up, only my personal observations from what tests I have done.

 

[jdieck]

One of the marketed said benefits of recirculating skimmers is the said lower power consumption. I have calculated the power consumption of the downdraft ETSS 1000 skimmer for up to 1000 gal tank with an Iwaki 70 with the Deltec AP703 for up to 800 gal with the three recirculating Eheims plus the feed pump and the power is the same at 190 watts. On the other hand the price is markedly in favor of the ETSS plus the eliability and trouble free maintenance of an Iwaki does not even compare to the trouble and maintenance of four pumps in the Deltec.
So I really think
a) The power consumption thing IMO is a mith. At the end for comparable performance you need to move the same amount of water either thru the skimmer or within the skimmer, this calls for a very similar power consumption if not the same.
b) Maintenance and reliability is simpler in simpler skimmers, add a needle wheel and the gap is even bigger
c) Other than vs Deltec against which everything else seems cheaper, the actual price difference is more on brand than actual performance.

 

[hahnmeister]

That is true in many cases... as you get into skimmers rated at over 300g, the needlewheel pumps start to add up, not push as much air per pump, etc... and you end up having to go with something short anyways with 5-6 needlewheel pumps on it each pulling 50 watts... not the way forward always! However, as always, needlewheels and the skimmer bodies they go on come down to one thing: the pump. Several needlewheels are simply impeller swaps with venturis... this does not make a good needlewheel. As a consequence, the pumps still move alot of water with air that is not much better than a beckett, and since most pumps on the market are like this, in most cases, yes, as you get over 300g, the efficiency of needlewheels loses out compared to becketts.

I wouldnt call the power consumption thing a myth. Both systems MIGHT move the same amount of water... MIGHT. The air water ratio of the better needlewheels is in the 2:1 range (water to air) while I still havent seen a beckett come anywhere close to this. So by your own basic concept of wattage = water moved, the needlewheels maintain an advantage.

Also, the basic thermodynamic principle of work done being applied only to the volume of water moved isnt the whole story. Becketts and their like rely on creating a pressure on the pump to then create a suction in the venturi... this is counterproductive. Moving a given volume of water against a higher back pressure means you are wasting much of its potential. Needlewheels rely on suction to create suction, thats it. No back pressure (maybe a slight restriction on the intake, but thats all). So while 900 gph through a needlewheel pump may only take 50-60 watts, the same pressure rated pump needed for a beckett/venturi/ETSS will be well over 100. Even with the back pressure on the pump slowing it down, its still more juice because the pump is pressure rated. Not to mention, the exact electric use will vary with each pump and venturi. Some pumps DONT see a wattage drop as back-pressure increases, but a wattage bump! (Iwakis, ReefFlos, etc). But lets take one case... a highly favored eheim 1260/62 pump. As a needlewheel, it can do more than 1200lph of air. As a beckett, the best I have ever seen is 600lph. And as commonly used that this pump is, its hardly one of the best needlewheel designs IMO. The volute is too restricted with that shaft support on the inlet, the impeller well should be wider and thicker, the outlet needs to be larger, etc.

The thing is, with the better designed needlewheels, this advantages are going to be more clear. A Sicce PSK 2500, although not one of my favorites, has a monster output for its wattage. 25 watts for 1200+ lph? Unheard of in beckett/ETSS land.

The 'monster pump' I have designed for ATB should spell it out pretty clear: 6000+ lph for about 130 watts. You cant touch that with an ETSS or beckett.

The problem is that so many needlewheel designs just arent done as well as they could be, with few exceptions: ATB's Airstar, RE's Red Dragon, and ATI's Sicce PSK 2500. Even the needlewheel hammerhead that ER is using hasn't really been optimised for needlewheel use... sure, it might make 7000lph of air, but its 300+ watts!