Large volume laminar flow machine

[karimwassef]

I went scuba diving in Cancun last week and came back with a strong desire to replicate the large volume laminar flow I experienced around the coral reef. As I work up some ideas, I wanted to see if anyone else has attempted this successfully (or not).

Let me describe what it is and isn't.

Any pump or surge outlet is basically a pipe. 1", 2", ...12" it's still a pipe. The powerheads, even the ones with wide flow patterns still pull water locally and then thrust it through a channel, even a wide cone channel. I'm still calling that a pipe. So this project is explicitly not a pipe outlet.

Now let me describe what it is that I want to duplicate... Imagine that you're a sea fan on a rock. That rock is in the middle of a big tank of static water. The rock sits on a cart/dolly/roller on straight tracks. The roller moves forward and backwards on the tracks so that the complete motion takes about 4 seconds and moves about 12 inches in each direction. Now, from the coral's point of view, the entire mass of water around you has moved forward and back. There was no 'flow pattern'. Every bit of water moved around you in a straight line in the same direction with the only turbulence caused by interference with the coral itself. No shear action. No vortices. No turbulence.

It literally feels like inhaling and exhaling.

So- to do that in a tank (where the corals don't sit on rollers)... is ambitious, I think.

First thought is to look at a fictional completely sealed square pipe (like a sealed tank including the top), with a pipe connected to the left wall and another to the right wall. The pipes are connected to a massive piston (or reversible DC pump) and to each other. As the piston moves, the same volume of water enters one side as exits the other. The inlet and outlet need to be huge and the laminar effect is only emulated in the middle of the tank away from the inlet and outlet. Still feels like pipes close to the walls.

Second thought is using a laminar flow creator. This is a box with hundreds of plastic straws in parallel that helps create the smooth flow. One box at each end? That may convert 'pipe' flow to a uniform laminar flow. Still not very good and takes up a lot of space.

Third is a moving wall the size of a side panel - with pistons to move it back and forth. The opposite wall would have the same in the opposite direction. If they move together at the same rate, they should smoothly move the volume between them (assuming they're not moving too fast).

Has anyone tried these ideas? Different idea? to get to this goal.

 

[karimwassef]

To be clear, I don't want to set up surface waves or standing waves by pushing flow and have it bounce back from the opposite wall. I want the entire volume to shift to the left and then to the right. No waves.

 

[slief]

That's essentially what I have in my tank. Tunze's on the back wall all pushing towards the opposite end 8' away. The turn on and off constantly sending a surge that rushes across the length of the tank hits the wall 8' away and then bounces back towards the power heads.
It took some experimenting with the on/off interval to get it to work but it works well with no dead spots and a good back and forth motion that is very visible.

 

[sleepydoc]

How does that work with your overflow?

 

[slief]

How does that work with your overflow?

No issues for me at all. My tunze's concentrate most of the flow to the lower 2/3rds of the tank while my Sea Swirls on my return cover the upper level and face the Tunze's. I get a 1" rise and fall surge at the surface every few seconds but it doesn't impact my overflow noticeably and given that my tank is totally enclosed by drywall and there is a lid over the overflow, the sound isn't noticeable with the doors closed. I also don't use durso's or anything in my overflow. I let the water crash through it for maximum aeration. I also have a pair of 2" bulkheads in the bottom of it so flow is never an issue.

 

[Bent]

I always thought it would be neat to have something that repeatedly drops something heavy in the water and lifts it out.

 

[callsign4223]

I always thought it would be neat to have something that repeatedly drops something heavy in the water and lifts it out.

You wouldn't need to drop something heavy into the tank, you could just push something buoyant down. I'm picturing something like a boat fender being pushed up and down by slow reciprocating motor.

 

[Bent]

You wouldn't need to drop something heavy into the tank, you could just push something buoyant down. I'm picturing something like a boat fender being pushed up and down by slow reciprocating motor.

Yeah that's true. Just something to displace the water.

 

[ericarenee]

You wouldn't need to drop something heavy into the tank, you could just push something buoyant down. I'm picturing something like a boat fender being pushed up and down by slow reciprocating motor.

Newport Aquarium up near Cincy has a Wave Aquarium To mimic a storm in the ocean floor there are some fish in there but i forget what kind. The tank is Prob 30 feet across 15 feet tall and not sure how deep 6-8 feet or so..

On each end there is Hydraulic cylinder that works like this.. One pushes down the other pulls up..Pulling and pushing the water thru slots . The Floats looked to me like plastic of some kind riding on some type of guide..

 

[karimwassef]

Thanks erica. I'll look into it.

I don't want a wave bouncing and reflecting back. This is not a wave machine.

If done right, the surface can be completely still. The whole volume moves forward and back.

If I'm making waves, then I don't have the laminar straight flow I'm looking for.

 

[slief]

Thanks erica. I'll look into it.

I don't want a wave bouncing and reflecting back. This is not a wave machine.

If done right, the surface can be completely still. The whole volume moves forward and back.

If I'm making waves, then I don't have the laminar straight flow I'm looking for.

And just what do you think will happen when the "whole volume" of water moves one direction in a closed space and the volume of water hits the wall? You don't think this will cause a wave?? I can guarantee you it will. The water that hits the vertical surface has to go some place when there is water behind it pushing the same direction. It will hit the wall and go up and down which will create a rise in the waters surface.

Edit: By the way, I'm not trying to be condescending. Just pointing out that if the flow will create waves.

 

[laverda]

What you want is exactly what wave boxes do when set up properly. Tunze and Wave2K are 2 examples. They gently move all the water in the tank uniformly back and forth. They work best in longer tanks then square tanks. Not really achievable with pumps alone.

 

[Gorgok]

Even if you did the amazing of putting the rockwork on a rack and dragging that back and forth you will end up just creating waves without the near infinity of the ocean to dissipate the return...

You could probably dissipate it some with a shallow ramp to an overflow at each end of a tank, but they would probably have to be as long as the tank or more... Even then some will come back as a wave.

 

[ericarenee]

Thanks erica. I'll look into it.

I don't want a wave bouncing and reflecting back. This is not a wave machine.

If done right, the surface can be completely still. The whole volume moves forward and back.

If I'm making waves, then I don't have the laminar straight flow I'm looking for.

I think i explained that wrong..
BUT What you are talking about could be maybe created With a Gate valve like configuration on each end.
This will take a very long tank.

So 10 foot tank. With 5 foot middle second 1.5 feet on each end.. Each end of the 5 foot section Have slots cut from right above the sand bed to 6 inches below the water .. Would have to experiment To get the right size slots and where to position them. I think horizontal would be best..

The top of the end boxes might need to be somewhat sealed at the top or the gate structure would need to seal the water from getting behind it. when it goes back it will push water up .. So maybe the top of the baffle would need to be a bit short so the back stroke of the gate would push water over top

Then have a hinge plate that can open and close.when open it will allow (kinda pull water into the 1.5 foot area. it would have to be timed with the other side Closing pushing its 1.5 foot area empty (or somewhat empty prob does not need to seal) ... This would cause the gentle wave your talking about ..
The one at the Aquarium.. Goes back and then up with Hydraulics if i remember right.. I caused the water to make waves at the surface and you could see the fish still able to swim in the lower wake...

You could control the speed and wake in the tank depending on the speed and sync of the Gates....

Just my Theory... If had time and energy to put into it i would test this on a smaller scale....
------------------------------------ off topic sorry---------------------------------
I Have a badly messed up arm and Limit what i do by Priority... its 1 hour working 6 hours on the couch with ice or 3 hours sleeping from pain meds..

----------------------Not Complain there are people far worse---------------

 

[karimwassef]

Thanks for the feedback. Erica and Gorgok, I see what you're saying. I was thinking of an 8 ft tank with 1 foot on each end dedicated to creating the translating water motion. Basically, I'd end up with a 6 foot viewable area and two feet of motorized areas. I hadn't thought of using slanted wall. I agree that the middle 3ft would be closest to the effect I'm thinking of. That's why this is so difficult and very different from a pump's flow.

Slief - If I was pushing water from one direction and hitting a solid wall, I'd get a wave. I'm not talking about that, I'm talking about both side walls moving so the volume shifts - translates.

I find the biggest challenge here on the opposite end of tank - far from where water is being pushed.

Let's say that I have a thousand tiny pumps on the left wall that take water from an external tank and inject it to the right. At the opposite end, that water needs to slow into another thousand pumps back up to the reservoir at the same rate. It can't have an overflow or a solid wall. The water coming in must be equal to the water exiting to avoid a wave.

 

[karimwassef]

My example of rockwork on a rolling frame was to explain what the coral experiences in this kind of motion. The actual movement of water away from the rock and coral would not be laminar, but the coral would experience the sensation of a moving ocean, at least for one cycle.

The bigger the tank, the more cycles that could be performed before the bounce back from the tank walls would disrupt the water at the source of the motion.

I'm only using this to define what I want the coral to experience.

 

[karimwassef]

Building on erica's idea...

So, how about an 8ft tank with false walls (1ft in) at each end and a sealed top connected to a DC pump and each other. Horizontal slits cut into the false wall close enough so that they simulate laminar flow. The inside of the wall could also have little ledges above and below the slits to extend the effective depth of the slits...

Now, the pump take water from one side and pumps it to the other side at the same rate (slow ramp, slow ramp down) and then reverses?

That sounds like it would do it?

 

[karimwassef]

When I say slow, I mean the overall rate at a point feels slow? But this would be a beast of a DC pump to move a 2' x 2' x 1' volume of water in 4 seconds... 27000 gph... Or split the feed to 5 DC pumps.

 

[slief]

Slief - If I was pushing water from one direction and hitting a solid wall, I'd get a wave. I'm not talking about that, I'm talking about both side walls moving so the volume shifts - translates.

I get what you are saying but lets assume you have a pump at either end. You would still be staggering flow to create the back and forth motion. When one pump fires up and displaces a 2'x2'x1' volume of water, kinetic energy will will cause the water on the other end of the tank to rise and fall even if to a minor degree. You already noted that you will need a pretty high amount of flow to create your desired flow. There will be a "ripple effect" from the burst of flow or even ramp of flow and having two pumps at opposite sides. The shifting the flow. The back and forth between the two pumps will have an impact on the surface just the same as having a single pump or pumps at one end.

 

[karimwassef]

That's why I said the biggest difficulty is extracting water from the right wall (sink), not pumping it in at the left (injection) wall.

I also don't see this working with two pumps. The same flow entering must be exiting.

As I pump water at the left wall, it begins a flow from left to right. Simultaneously, I'm pumping water out on the right side, pulling water from left to right also. The effect is a sideways shift.

No system is perfect and in a real tank, there will be waves and ripples. I'm not saying that's bad. I'm just saying that waves are not the goal. Not traveling or standing waves.

Most water movers are "wave machines". I want to be clear that this is not a wave machine. Incidental waves will occur, but the point is to move a laminar block of water. That's different.