Large volume laminar flow machine

[karimwassef]

Close up

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The corners are made of 6" PVC pipe cut against the edge and mounted after the acrylic is assembled.

The high top is like a second little acrylic tank that is screwed in place into the top of the main acrylic section.

So far, it seems viable. What do you think?

 

[herring_fish]

Wow!

 

[karimwassef]

The carriage needs to move at 1ft/s for 6 seconds covering 6ft. Back of the envelope~ power needed to move the water is 400W. That's assuming lossless power transfer.

I have no feel for the efficiency of these kinds of drives.

 

[karimwassef]

Oops recalc. Make that 2100W (damn back of the envelope didn't do units)

That moving a cross-section of 11.5" x 20" a distance of 72" in 6s, continuously.

It doesn't include losses which means it's too low.
It also doesn't include the fact that the velocity profile is sinusoidal with 1ft/s being the peak velocity amplitude. So the loss calculated is too high.

 

[ericarenee]

It looks great .

One Question.. The 8 1/2 inch area after before the display area might need to have short baffles between the ones that are there say 7 inches long. to keep the water moving in channels all why to the plate.... Thou not sure 8 inches is enough to change the water force...

 

[herring_fish]

OK I have to see if I am getting it right. Often, I am at work when reading the so I don't concentrate on it enough to get everything right but"¦
LOL "¦.that hasn't stopped me from making suggestions.

1. Have you changed the scope to get 6 feet of displacement in the back, at 3 to 1 ratio, to get 2 feet of displacement in the display tank, not 4 inches? Or have I read something earlier or now in my typical dyslexic way?

2. Why do you take up that rectangular area that has the 10" dimension in it? Could you take that back so that the side areas (that go from back to front) could be the same width as the back area? It looks like this area pinches down to limit flow. Am I just not looking at it right.

3. Also, can you heat and bend acrylic to use in the corners of the side baffles instead of using PVC? It looks like the back sides of the corners are sharp to disrupt laminar flow. The workmanship would not have to be pristine.

4. The three paddles are just being shown at both ends of the stroke? There is only one set, right?

Finally, (and this is not a rhetorical question. I really don't know.) Am I right in thinking that when you move one part of the tank water, you are moving it all so you have to calculate for that?

 

[Gorgok]

Finally, (and this is not a rhetorical question. I really don't know.) Am I right in thinking that when you move one part of the tank water, you are moving it all so you have to calculate for that?

That would probably be true in a sealed system. But when paddling in the ocean you aren't moving the whole thing or oars would not be very effective =P. I imagine there are enough paths to dissipate the energy of the paddles that you don't have to account for most of the water in this as well. Probably more so than in the ocean though, as it is being channeled.

 

[karimwassef]

It looks great .

One Question.. The 8 1/2 inch area after before the display area might need to have short baffles between the ones that are there say 7 inches long. to keep the water moving in channels all why to the plate.... Thou not sure 8 inches is enough to change the water force...

Agreed. There's plenty of design variables still in play. I think secondary baffles will likely be needed.

 

[karimwassef]

1. Have you changed the scope to get 6 feet of displacement in the back, at 3 to 1 ratio, to get 2 feet of displacement in the display tank, not 4 inches? Or have I read something earlier or now in my typical dyslexic way?

The channel is 1ft, the display is 3ft. So 3:1 x. The display flow is 4in/s, so the channel is 12in/s.

2. Why do you take up that rectangular area that has the 10" dimension in it? Could you take that back so that the side areas (that go from back to front) could be the same width as the back area? It looks like this area pinches down to limit flow. Am I just not looking at it right.

That's the overflow. If not here, then where?

3. Also, can you heat and bend acrylic to use in the corners of the side baffles instead of using PVC? It looks like the back sides of the corners are sharp to disrupt laminar flow. The workmanship would not have to be pristine.

I don't have that competency. It has to bend and still be perfectly flat on the top and bottom.

4. The three paddles are just being shown at both ends of the stroke? There is only one set, right?

Yes.

Finally, (and this is not a rhetorical question. I really don't know.) Am I right in thinking that when you move one part of the tank water, you are moving it all so you have to calculate for that?

That's wishful thinking IMO. I've been looking at this using analytical approximations and the math of bulk water waves is not easy. Especially because we're driving it over and over. Without a CFD model, I can't predict it meaningfully.

 

[karimwassef]

That would probably be true in a sealed system. But when paddling in the ocean you aren't moving the whole thing or oars would not be very effective =P. I imagine there are enough paths to dissipate the energy of the paddles that you don't have to account for most of the water in this as well. Probably more so than in the ocean though, as it is being channeled.

Sealing this mechanism in an acrylic tube was the key to creating a syringe like effect where you push and it moves forward, not up. I'm still concerned that the waves may be so high that the shaft + slot assembly may also need to be sealed (or raised).

The output will look like a bulk wave push, I think. Predicting the actual flow of the 360gal in the middle is harder. I need an analytical model or a CFD tool to predict it.

Turns out that pushing water and having it go where you want in an open top is not a trivial problem...

 

[herring_fish]

Just getting my head around it.

Just getting my head around it.

1. Have you changed the scope to get 6 feet of displacement in the back, at 3 to 1 ratio, to get 2 feet of displacement in the display tank, not 4 inches?

I'm just talking about the distance that the water moves past a given coral in one direction total not inches per second. You say that I have read you correctly on the 3:1 so if you move the paddles 6 feet, then the water in the display would move 2, right? I thought you were talking about 4 or 5 inches total, not two feet. Not that is a bad thing at all. I'm just trying to pin down the scope.

2. Why do you take up that rectangular area that has the 10" dimension in it? Could you take that back so that the side areas (that go from back to front) could be the same width as the back area? It looks like this area pinches down to limit flow. Am I just not looking at it right.

"œThat's the overflow. If not here, then where?"

I may still be misunderstanding, sorry. I'm not talking about the dark purplish area, just the stuff in the little rectangles, at the ends where the dimension actually is.

Finally, (and this is not a rhetorical question. I really don't know.) Am I right in thinking that when you move one part of the tank water, you are moving it all so you have to calculate for that?

"œThat's wishful thinking IMO."

Undoubtedly, you are correct completely but if it were truly laminar, without big waves or in a tube, it might happen in a perfect world and if it did, that would be a worst case. Again, I am just looking at scope.

If movement is dissipated or transferred out of phase, then you might be moving 200 pounds. If it all moves then you may be talking a ton and a half.

 

[karimwassef]

In terms of travel distance - you're right. The 6ft of travel is not necessary for a 12" channel. The paddle distance needed is only 15.3in to get to 4in/s. That would translate to 15.3/3 ~ 5in in the display. This is because the injection velocity and position profiles are sinusoidal. That will reduce the power needed (I think). I need to go back to redo the back of the envelope with a shorter travel and sinusoidal velocity.

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The little rectangles on either side of the overflow are there to channel the flow in the bottom baffle. If you remove that area, that baffle would have no travel after the turn. There would be no distance to align the flow.

I already think that the little 6" of travel is too small to align the flow. Taking the box out would leave a chaotic output after a turn. The other channels have different distances. Top ~ 12". Second is 10". Third is 8". Fourth is 6". I can't see an alternate solution right now, but let's keep thinking.

The volume being moved in each 6 second cycle is ~15in x 12in x 20in. That's 16 gal for each 6 seconds. The main tank sees 5in x 36in x 20in = 16gal. That's 130lbs per 6 second stroke.

This might mean that the injection channel can be reduced to 3" and then span the full 6ft of travel. The injection channel inlets are 2.5" wide now and the side channels are only 1" wide. If we cut back the width of the main injection channel, the inlets would have to shrink commensurately. That probably limits the injection channel to 5" at the smallest... more design variables .

I'll redo the power loss before we iterate.

 

[Fiziksgeek]

I only skimmed the thread, but what you are trying to do reminds me of gyre flow. Here is a reference from 2007

 

[karimwassef]

Excellent article! Thanks Fiziks and welcome.

Yes, the concept is similar to a gyre but with a few differences:

1. The flow is not channeled into a narrow cross-section using dividers in the tank. The idea is to look natural but still create the same effect.

2. The flow is spread across the full and very wide cross-section (3ft) of the tank. So the entire tank water needs to flow like a gyre.

3. The flow alternates frequently. The gyres described in the article flow in one rotation for a long time, then alternate.

The flow description and benefits are accurate though.

It also highlights some basics that we need to incorporate...

1. Removing more surface waves by creating a deeper underwater channel.

2. Raising the flow from the bottom to avoid blowing sand storms.

 

[karimwassef]

In terms of travel distance - you're right. The 6ft of travel is not necessary for a 12" channel. The paddle distance needed is only 15.3in to get to 4in/s. That would translate to 15.3/3 ~ 5in in the display. This is because the injection velocity and position profiles are sinusoidal. That will reduce the power needed (I think). I need to go back to redo the back of the envelope with a shorter travel and sinusoidal velocity.

I really shouldn't do math when I'm tired

The 4in/s is the peak velocity in the display.
That means that the peak velocity is 12in/s in the channel.
Using the same math above, but with the actual desired peak speed, the result is ~ 45in in each direction in the channel. Still not all 6', but a pretty hefty swing at 12in/s peak velocity.

That would mean that the travel in the display is 15in in each direction ... at a peak speed of 4in/s.

The average power is about 1000W.

 

[karimwassef]

Here's what I think will happen. This is just a zero order 1D analytical calculation.

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

 

[herring_fish]

It's looking good at 12 seconds. What are all of the colors? I get most but not all of them. Would you be able to simulate the height of the surface wave in the DT?

 

[karimwassef]

Which colors? In the graphs or on the tank layout?

 

[karimwassef]

This is a zero order model, so not anywhere near modeling the trochoidal waveforms that could result at the outlet. I've given up on the modeling for now. I'll build a small 24:1 model (2.5" x 5") and use a linear actuator with a little control board to control acceleration.

The properties of the fluid would need to be mapped so that it simulates what a large body of water would do. So, I can't run water... I would need to make a less viscous material (I think). I have to go back to those old scaling rules to get it right.

 

[herring_fish]

Dude,

Where did you learn this stuff!?! Very cool!

Oh I'm talking about the colors of the simulation. When I went to school, they didn't have this stuff on the net.