Neptune Aquatics

Flow Advice

Natterjak

Natterjak

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So I've been thinking about this on and off for a while, wondering if I need to adjust the flow in my tank. Things seem to grow fine, but I do worry about dead spots with my current setup.

In my 180 (6x2x2), the flow is provided by a closed loop run off a Dart pump and an OM 4-way - there are two sets of returns (4 outlets each). The first set is near the bottom, pointing from the back of the tank to the front. When the OM switches, the flow is then diverted to the next set of returns, which come up from the bottom of the tank, near the front, and point 45 degrees up and towards the back to the overflow. There's a Mag12 in the sump that feeds 4 returns that point straight down the back. The idea then being that there is a circular flow pattern in the tank.

My main two concerns are that most of the flow is concentrated in the stream of the nozzles (simple 3/4" PVC), and that there's not really any side-to-side flow in the tank.

I've thought about replacing the Dart with a bigger pump, but I don't know if that would solve either of those two problems (if they are actually problems). I've talked to Paul at Oceans Motions about adding Tunzes or Vortechs, but he says that will defeat the purpose of the circular pattern.

Anyone have any thoughts? Would it be beneficial to add Vortechs or similar, or should I just leave it alone?
 
IMO, there in no point in running an OM if you want a circular flow pattern. It just sounds counter productive to the way a gyre tank should be set up. I would get a bigger pump and ditch the OM 4-way leaving all 4 points of entry in the closed loop always open.
 
agree. OM switches too fast to allow circular momemtum to reach any steady state. It's better imo, for generating turbulence. If you want to play with more flow, try the easy "test route" and put in a Koralia 4 or one of the new koralia mega PHs. There is something awesome about big wide flow patters of vs the typical jet flow.
 
You can probably use the OM still to get localized "surges" if you just put 45* or 90* fittings on all of your returns and have them pointed in the same gyre-direction. Not sure if that sentence made any sense, but with all the water moving in the same direction you should get a gyre. If you wanted alternating gyres, then maybe you could have 3 returns pointed in the same direction (sequentially) and have the 4th and a koralia or something pointed in the opposite direction. Maybe?
 
[quote author=phishphood link=topic=6945.msg90087#msg90087 date=1237425255]
You can probably use the OM still to get localized "surges" if you just put 45* or 90* fittings on all of your returns and have them pointed in the same gyre-direction. Not sure if that sentence made any sense, but with all the water moving in the same direction you should get a gyre. If you wanted alternating gyres, then maybe you could have 3 returns pointed in the same direction (sequentially) and have the 4th and a koralia or something pointed in the opposite direction. Maybe?
[/quote]

It won't work as well as a single continuous point of flow. That is what builds a gyre.
 
I understand it's not a point source, but with them all pointing in the same direction, wouldn't the net result be the same?
returns on the back from left to right: straight, 90* left, 90* left, 90* left
returns on the front from left to right: 90*right, 90*right, 90*right, straight

Wouldn't this result in a net gyre rotating ccw viewed from above?
 
I don't think it would. You are not building on the same flow. The point of a gyre is to move a bulk area of water. You need continuous flow to be able to create a bulk flow of water. Like I said earlier its counter productive to use the OM 4 way even if all the outputs are pointed in the same direction (direction of flow) like Bonnie already mentioned in her first post.
 
I thought her main problem was the lack of side to side motion. The way in which she's trying to create the gyre currently is in the 2x2 square vs the 6x2 rectangle. Something about shear forces maybe (don't remember my hydrodynamics) but the longer time that the water is in a (relatively more) linear flow it should pick up more water to move more and more mass before hitting a boundary.
 
Rereading advanced aquarist and it's mentioned that a a chauvet lighting timer was used to switch 2 sets of pumps on and off. Article here: http://www.advancedaquarist.com/2007/1/aafeature#h6

While I am in no way trying to say it can't be done in a simpler manner with koralias or different plumbing, I was just trying to do the most with the least amount of changes to the system. And hoping to not sound like an arse, especially in saying this, but I'm not trying to start an argument either, but more for my own clarification and learning.
 
FWIW the author uses no switching of currents in any of his tanks (as I sit here and look at them). He uses a single MP40 on a 29g and another on a 90g FO system :)
 
At least I sourced the info this time :)
"Once again a Chauvet light timer was used to alternate the flow between two circuits of powerheads. Each circuit contained pumps which were diagonal to each other and in this fashion the force of both pumps were working together to move the entire water mass"

January 2007
 
[quote author=phishphood link=topic=6945.msg90108#msg90108 date=1237428702]
At least I sourced the info this time :)
"Once again a Chauvet light timer was used to alternate the flow between two circuits of powerheads. Each circuit contained pumps which were diagonal to each other and in this fashion the force of both pumps were working together to move the entire water mass"

January 2007
[/quote]

Critical info missing. If you take the above as an all inclusive statement, that means that switching pumps every 0.0001 sec and every hr has the same net mobility change. Switching rate and equilibrium rate (or approximation or even commentary on it) are vital.
 
[quote author=phishphood link=topic=6945.msg90108#msg90108 date=1237428702]
At least I sourced the info this time :)
"Once again a Chauvet light timer was used to alternate the flow between two circuits of powerheads. Each circuit contained pumps which were diagonal to each other and in this fashion the force of both pumps were working together to move the entire water mass"

January 2007
[/quote]

I don't see how that explains what the OM 4 way is doing. In the authors case he was alternating the gyre at long time intervals. With the 4 way it changes very rapidly (every 1-2 seconds). Huge difference.


As Tony was typing his technical answer, I came up with the layman's answer.
 
Heh, sorry Tony. That last quote of mine was just to prove I didn't make up the chauvet part, in reply to Gresham's post. Full section as in the article is as follows:
Gyres in Reef Aquariums

An aquarium does not necessarily need a divider to produce gyres of the water mass. Although the water movement will not be as complete and uniform as it is with a gyre tank, it is still advantageous to encourage water movement to follow a circuitous path. In a reef aquarium with live rock and coral on the bottom, the water surface of the aquarium provides the least resistance to moving water. Because of the lack of friction, moving water which is directed in this region will produce the most momentum of the water mass. If there is an even transport of the surface water from one side of the aquarium to the other, the entire water mass should begin to gain momentum as it is moved at both ends. At one end of the aquarium, the water will begin to “pile up” and then sink down. At the other end, water will rise up to replace the volume which is displaced by the water motion. Although it is easiest to create gyres which follow the top and bottom surfaces of the aquarium, this is not the only way to create gyres. Figure 4 is a photo of a 180 gallon aquarium with an overflow drain right in the center of the tank. This aquarium contained a modest amount of live rock and it was circulated by encouraging mass water movement around the center overflow. Once again a Chauvet light timer was used to alternate the flow between two circuits of powerheads. Each circuit contained pumps which were diagonal to each other and in this fashion the force of both pumps were working together to move the entire water mass. The center overflow was not necessarily the most aesthetic design but it was very easy to spin water around it using only very modest water pumps.
figure4.JPG

Figure 4 Because this 180 gallon was circulated using mass water movement techniques, only modest equipment was required to produce adequate water motion.

Not only can mass water movement techniques help aquarists produce higher water flow speeds in the aquarium but it can also encourage more water movement through the interstices of live rock and corals with open growth forms. Normally an aquarist might target one or more plumes of water movement at corals which require fast water flow speeds. In this scenario, the turbulent water flow plume encounters a lot of friction on its way to the desired location of the reef aquarium: it will experience resistance from the still water around it, it will experience drag from the shape of the corals it encounters and the turbulent nature of the water flow plume will do little to preserve the momentum of the water movement. In a scenario with the employment of mass water movement, the behavior of the fluid will be much different. The plume of water motion from the same source will encounter less resistance from the water around it since both parcels of water are moving in the same direction. The decreased resistance will straighten out the flow and preserve more momentum. Not only will the water be moving faster once it reaches a coral, since water is moving away from the coral on the downstream end, water will be forced through the normally stagnant water which is present at the interior of corals with open growth forms. Figure 5 shows an aquarium where dense coral growth account for a significant portion of the aquarium’s cross section. When using mass water movement techniques in cases of dense coral growth, water flow speed can actually accelerate as more water is pushed through spaces with a smaller area. Aquarists who wish to encourage additional water movement at the inside of dense coral colonies will see great benefits from using mass water movement techniques.
Click to expand...
 
::) Jake is a good friend of mine. I've not only read that article a dozen times, I've caught his presentation nearly as many times :D Luckily he's moved onto other subjects as I think I can give his talk on my own :lol: (didn't I mention I was at his house right now?)

FWIW he said he still believes in a slow switching of a laminar flow but the key point is slow. (he made me say that) An OM4 is far too fast. You could put it on a timer. I'd still re-plumb the set-up to have the majority of the flow pointed towards the surface.
 
In regards to the time, I understand what both of you are getting at (and also sorry for missing the time period used on the chauvet, don't know why I skipped out on that section). I was trying to see if the plume of water from each/any of the returns would encounter less and less resistance from the surrounding water as time goes on if the water column eventually momentum in the direction of the rotation.
 
And I really need to turn off the post w/out getting the warning of new posts since the last view. Gresh, thanks for the first hand info, and thanks again everyone for the enlightening :)
 
IF they are all pointed to produce a single direction gyre then yes, what you are saying is pretty much spot on. You get less resistance from the surface of your tank then any where else (hence my suggestion to re-plumg and point towards the surface).
 
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