Airtight

[karimwassef]

Is there any difference in an acrylic or wood-epoxy tank construction if it's meant to hold air pressure/vacuum vs. just keeping water in.

So - if you were to build a raised tank (inverted tank in tank + vacuum out the top air), would you build it any differently?

https://youtu.be/I7N2gB7eQ04

https://youtu.be/zgKTwRIC4ZI

https://youtu.be/qJprKL_24ZA

https://youtu.be/nXSTOZ0f8Jc

https://youtu.be/1tmsHa5spqc

[karimwassef]

http://images.realclear.com/381619_5_.jpg

http://static.boredpanda.com/blog/wp-content/uploads/2017/01/inverted-aquarium-pond-luxusburger-fb.png

http://img2.etsystatic.com/000/0/6955141/il_fullxfull.341824166.jpg

http://img.youtube.com/vi/IVmJRV_Tn40/mqdefault.jpg

[karimwassef]

http://stagevu.com/videos/inverted-tank

[karimwassef]

My questions goes to both material thickness as well as adhesion methods...

Basically, if the pressure is based on outside air pushing onwards (vs water pushing out), how thick does the acrylic need to be?

I would assume that it's just enough to avoid it being crushed by the outside air which is less than the usual pressure of the water in the tank. So following normal tank rules should be safe.

[karimwassef]

Oh... one more question. If the tank was filled and emptied and then filled and emptied again... over and over. How would the tank constructions change?

Assume it's like 30" higher than the 1atm air water level

[mcgyvr]

No difference..

[der_wille_zur_macht]

Empty/fill cycles mean a lot of stress compared to a static load. Personally, I would shoot for a much higher safety factor (like, 10-12 instead of the 5-7 that seems common with tank builders).

[sleepydoc]

For the static case, I would think that the stresses would be a bit easier to manage since the pressure would be pushing the sides together (at least for some of the seams)

I'd have to actually think more about the equations, but the pressure on the seams should be the same. Outward water pressure at the bottom of a tank is essentially the distributed sum of gravitational force of the water above. You have the same gravitational force pulling down, and since water is noncompressable, it wouldn't get attenuated at all.

Wille is correct, though in that emptying and filling will add more stress.

The other thing to consider is that any oxygen bubbles will accumulate and expand d/t the relative vacuum at the top. You also need to ensure adequate circulation to ensure the oxygen doesn't get depleted since there's going to be no surface for gas exchange.


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[der_wille_zur_macht]

In order for the container to stay full of water, there basically needs to be a vacuum inside it equal to the weight of the water. is that what you meant when you said the forces would be pushing some of the seams together?

These types of systems are really fascinating. It would be an interesting way to make a surge - have a powerful air pump on the inverted container, suck the air out until it's almost full, then open a valve to atmosphere (or shut the pump off). Boom, all the water pours out the bottom of the container. Shut the valve just before the water level reaches the bottom of the container, and you can ensure a massive, quick, bubble-free surge.

[karimwassef]

This is only one section in a much larger system. The water in the main tank will be well aerated and the water will be exchanged regularly.

I tried some experiments with thin wall plastic containers - I expected some collapse and I was surprised at the speed and force! I added in internal rib for support and that worked better. I've since made a PVC skeleton but haven't tested it yet.

Internal structure is really important here.

[karimwassef]

Yes. The application is a vacuum actuated surge.

This solves an old problem that I've had in my surges where round pipe outlets create inadequate flow shapes.

I'll post the video to show it working.

[karimwassef]

<a href="http://s1062.photobucket.com/user/karimwassef/media/CB854D3D-BA1F-4C51-893A-A6A0F58D4E07_zpsgh01zvly.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/CB854D3D-BA1F-4C51-893A-A6A0F58D4E07_zpsgh01zvly.jpg" border="0" alt=" photo CB854D3D-BA1F-4C51-893A-A6A0F58D4E07_zpsgh01zvly.jpg"></a>

There's a 1" x 12" slot at the bottom for the surge to flow out of

[karimwassef]

Stronger skeleton

<a href="http://s1062.photobucket.com/user/karimwassef/media/A7695CAE-B1EC-4A22-9D65-48B51640B999_zpsrusokru9.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/A7695CAE-B1EC-4A22-9D65-48B51640B999_zpsrusokru9.jpg" border="0" alt=" photo A7695CAE-B1EC-4A22-9D65-48B51640B999_zpsrusokru9.jpg"></a>

And the system with actuators. These aren't perfectly airtight so the vacuum will need to come on intermittently to compensate until I have something better.

<a href="http://s1062.photobucket.com/user/karimwassef/media/B5062018-4608-4C6C-9E93-01ADDEEDE3CD_zpsazxudyat.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/B5062018-4608-4C6C-9E93-01ADDEEDE3CD_zpsazxudyat.jpg" border="0" alt=" photo B5062018-4608-4C6C-9E93-01ADDEEDE3CD_zpsazxudyat.jpg"></a>

[karimwassef]

The concept is actually to couple multiple chambers to create multi-surge circulating flow effects

[karimwassef]

Here's some more detail on the design concept.

I've chosen a vacuum and modeled its suction based on what I can find online (not a perfect model)

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/2_zpsibykudka.png.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/2_zpsibykudka.png" border="0" alt=" photo 2_zpsibykudka.png"/></a>

based on that and a 2' x 2' x 8' chamber, I modeled the fill rate based on the flow.

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/1_zpszlqzqgui.png.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/1_zpszlqzqgui.png" border="0" alt=" photo 1_zpszlqzqgui.png"/></a>

So, even 1.5 mins, I expect the chamber to fill with about 120 gals that can surge through the tank. I plan on having 4 of these tanks with two more higher flow surges.

[karimwassef]

The double surge/circulating flow comes in by coupling the air tanks

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/0_zpsxaa0fmfg.png.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/0_zpsxaa0fmfg.png" border="0" alt=" photo 0_zpsxaa0fmfg.png"/></a>

The idea is to allow the tanks to share air and create suction back up in the "empty" tank while the full tank releases. This is to make sure the reverse flow is as strong as the forward flow.

Then I alternate suction to the other tank and repeat to create a large volume flow back and forth that rocks the entire reef (without rough pipe outlets or pumps)

[karimwassef]

I have to admit that this has been a dream of mine to find a way to create massive water motion in a loop without pumps. Actuators failed and I was going to rely of massively parallel powerheads with a common back chamber. This takes up a lot more room but has no impellers in it at all.

I believe that impellers cause massive death to plankton and limit the generational links of new organisms reproducing in our tanks. This could even have mariculture implications. The use to air pressure instead allow for zero mechanical contact and very high control of flow, even very high flow.

[karimwassef]

I'm also creating two surge/scrubbers that pull water up into vertical tanks that are sunlit. These are intended to grow algae out of the tank, but still allow herbivore fish controlled access to the algae on demand.

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/1_zpsr59a5zqj.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/1_zpsr59a5zqj.jpg" border="0" alt=" photo 1_zpsr59a5zqj.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/1_zpsteccflu4.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/1_zpsteccflu4.jpg" border="0" alt=" photo 1_zpsteccflu4.jpg"/></a>

This basically creates a closed loop of food without having the waste accumulate in the container since the surge would realease it back into the tank (yes intentional).

So, it's a surge/scrubber/feeder that is both wet and dry and sunlit. :)

[karimwassef]

here are a few more design views. I expanded the chambers to be 2' x 2' x 8' here... still works just takes a lot more space.

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/0_zpsijcpejsq.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/0_zpsijcpejsq.jpg" border="0" alt=" photo 0_zpsijcpejsq.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/2_zpsj8pee5nt.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/2_zpsj8pee5nt.jpg" border="0" alt=" photo 2_zpsj8pee5nt.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/3_zps9s7kdobv.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/3_zps9s7kdobv.jpg" border="0" alt=" photo 3_zps9s7kdobv.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/4_zps1ljnpi6j.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/4_zps1ljnpi6j.jpg" border="0" alt=" photo 4_zps1ljnpi6j.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/5_zpsuneeh7nk.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/5_zpsuneeh7nk.jpg" border="0" alt=" photo 5_zpsuneeh7nk.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/Designs/6_zpsefi6sylt.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/Designs/6_zpsefi6sylt.jpg" border="0" alt=" photo 6_zpsefi6sylt.jpg"/></a>

models are included for scaling. :)

[karimwassef]

ok. Here is last night's experiments video. Please ignore the mess :)

<iframe width="560" height="315" src="https://www.youtube.com/embed/pZyZlndTMSQ" frameborder="0" allowfullscreen></iframe>

My conclusion is that thin wall vessels could be used with enough of an internal supporting structure! Yay - it all got cheaper.

[karimwassef]

Here's my main thread by the way

http://www.reefcentral.com/forums/showthread.php?t=2589632&page=20

and here's the original multi-model circulating flow thread

http://www.reefcentral.com/forums/showthread.php?t=2519480&page=28

[karimwassef]

Oh and the reason for the larger shallower tanks 2' x 2' x 8' is to allow for larger slugs of water volume. Increasing the reservoir capacities to 240gal each means that there's the potential for two tanks to empty as two tanks replenish - but only at half volume (since the equilibrium point is halfway full on both tanks)

With four x 120gal, that means that the circulating slug of flow is only 60gal per tank with two sending water and two pulling water. That's a combined total of 120gal only. So with a 4 channel, 4 reservoir system, the maximum volume flow is the reservoir tank volume.

So increasing it to 240gal gives me more punch.

The DT is 8' x 10' (really 12' for 2' is dedicated to the flow chambers and surge). It's 27" deep so that's 1350 gals. 240 gal is only 18% of the water volume moving in the flow loop. That's probably ok, but just barely.

I still need to see how effective the air balancing really is and if it can really generate a reverse surge up into the second reservoir.

I'm concerned that the chambers are not just exposed to the normal pressure of the water weight. By coupling them and allowing the air flow between the higher and lower pressure to equalize, the force on the structure is really much higher over a shorter period of time.

My wife (also an engineer) says that the thin wall tank that's experiencing the sudden exposure to the vacuum will implode if it happens too fast. Either that or the seals will fail or the valves will... basically catastrophic event... so, need better math.

[karimwassef]

I'm open to putting the sketchup model on a sharesite like Dropbox if that'll make it easier to look at the details of the model. Let me know if you would like me to add you

[McPuff]

This would be really cool if you get it to work the way you want. I'd love to see a tank without pumps. How will you block the noise created by the vacuums? Or would you use some other type of industrial air pump? Your designs look very cool as always!

[karimwassef]

The vacuums will be in a separate room and insulated with an outside vent. I don't know how effective that will be but moving air instead of water allows tremendous design flexibility.

I also have to say that there's a reciprocal design suggested by Danny that uses air pressure instead of a vacuum. It's feasible but I prefer the vacuum - safer IMO.

[NeverlosT]

It just seems that a geared down motor pulling up a large area sealed piston in a tank that is partially submerged, effectively "drawing up" the water level slowly in the inverted tank, then the piston reaches and passes the height of a hole in the tank leading to atmospheric pressure and all of the trapped water would rush out the bottom. The piston then slowly descends and repeat. Would be relatively easy to make, no air pumps needed, would be silent other than the whoosh of air as the water drains. You could run it at whatever frequency you want for slow/fast surges. The air pump idea does not strike me as sustainable for a long period of time.


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[karimwassef]

pistons require seals that I don't know how to design or maintain. They also take up the room for the tank and plunger to actuate. The vacuum achieves the same without mechanical devices. More mechanical parts = higher failure rate.

In turns of actuating the release, it's the same. A sensor opens a valve when the water is high enough.

Keep in mind that the cost of a mechanical implementation is many times that of a tank with a vacuum attached.

[karimwassef]

rather than posting in multiple locations, I'm moving the results to my main thread :)

http://www.reefcentral.com/forums/showthread.php?t=2589632&page=20

[karimwassef]

<iframe width="560" height="315" src="https://www.youtube.com/embed/18ZsggRjOPI" frameborder="0" allowfullscreen></iframe>

I'm confident now that with sufficient internal bracing, I can build a larger system that can surge and countersurge using air pressure. Given the scale though, I might go with wood and epoxy.

[der_wille_zur_macht]

That's crazy. You're moving a lot of water very very fast.

[karimwassef]

Thanks. That's the idea! Check out my main thread. Lots of design options still in flux