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Discussion of laminar vs turbulant flow

47K views 93 replies 24 participants last post by  David Lund Photography 
#1 · (Edited)
Hey y'all,

Niko and I had a really stimulating talk the other day about flow regimes in planted aquaria and it got me thinking. His example of laminar flow in the San Marcos in a previous post is awesome and I thought I'd expand on it a little. After keeping planted tanks by rote for so long, having a deeper understanding of the science behind what's going on in my aquaria has helped me immesurably. I thought I'd talk a little bit about what I've learned in the hopes it'll increase your understanding of your aquaria and improve your hobby just as it has mine.

Reynold's number (Re) http://en.wikipedia.org/wiki/Reynolds_number

The initial statement "...such as laminar or turbulent flow: laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion, while turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities." contains the critical element' smooth, constand fluid motion vs. chaotic and other flow instabilities.

Going back to the San Marcos and other plant-filled streams many of us have seen; the flow in such streams is for the most part laminar. It may not be purely unidirectional and constant throughout the water column; however overall the stream flow isn't chaotic. Considering channel morphology; such streams are characterized by a general broad U shape. This is important! Although discharge may be high, the open nature of the channel allows for high flow with little impediment. Such flow regimes are beneficial to aquatic vegetation for multiple reasons:

1) Low shear forces- Although shear stress is present in all natural fluid flow situations; eddies and other turblent flow instabilities are areas of high localized shear stresses. We see this in our aquariums when using spray bars. The flow nearest the outlet is very fast relative to the area around it. This differential velocity creates eddies and vortexes in which shear forces can cause plants to lift out of the substrate or which can tear leaves off the stem; thereby damaging the plant.

2) Chaotic flow (high Re) likewise creates zones of increased and decreased water movement. We see this characterized by zones of deposition and resuspension of mulm in our tanks. The zones of high flow receive good input of nutrients and CO2; whereas the zones with low flow may be deficient in one or the other. Likewise, the deposition of mulm can create zones of localized water quality instability and become a source of harmful chemicals.

Consider the placement of filter outputs for a moment. The convention of placing the filter outflow on the side of the aquarium rather than the back aids in the creation of laminar flow. Why? The increased length of flow helps to disperse the energy related to filter discharge. The farther the stream travels before hitting an impediment such as the side of the tank, the greater the impact viscosity plays in the flow dynamics. Conversely, if I put a spraybar or other outflow on the rear of the tank facing the front, the short distance between the initial outlet and impediment decreases the contribution of viscosity which causes an increase in energy when the flow hits the impediment. The higher the flow energy at point of impediment, the greater the Reynold's number, and the greater the turbulence of flow at the point of impact.
Using the below equation we see the following:



Given a constant viscosity, discharge velocity, and density of water leaving our filters; L, distance to impediment or width of stream flow is the characteristic which defines flow regime. If L is small, Re will be large. If L is large, Re will be small. Remember, we're multiplying L by two constants and dividing by another constant. The greater the pVL term the lower the overall ratio.

What the hell does this mean for my aquarium? In order to create an environment with the greatest potential for laminar flow we must set up a situation where either L is high or V (discharge velocity) is low. To use my aquarium as an example. I have spraybars placed along the substrate surface and tank sides which face the front of the tank (small L). In order to maximize laminar flow potential I have to decrease V. Assuming my pump is always discharging at a constant rate and the viscosity and density of the water leaving the spray bars is constant, I must either increase the size of the holes in the bar, increase the number of points of discharge, or both in order to reduce the Re.

Why would I care about that? Don't I want the highest velocity possible from my spraybar to suspend mulm so it can be picked up by the filter or transport it to a place where I can syphon it out? No!!!!!!! Remember, high V creates turbulent flow which, in turn, creates flow instabilities as discussed above. I want smooth, laminar flow to uniformly distribute water. This uniform flow distribution may be slower than turbulent distribution, but it is more effective in both nutrient distribution and removal of undesireable materials from the water column over the long term. Why?! Because laminar flow reduces differential zones of suspension and deposition. The greater the proportion of zones of suspension to deposition, the greater the volume of particles removed from the water column OVER TIME. This is the big secret and science behind the Lily Pipe and convention of placing the filter outlet on the side, rather than back, of the aquarium. Since stability is, by definition, a characteristic of change over time, one must consider efficacy over time rather than instantaneous or immediate efficacy. Turbulent flow can improve results in the short term, that's why we stir the water in planted areas at times when cleaning our aquaria. The instantaneous turbulence suspends the particles we want to remove. In general, however, this is not a desireable condition.
 
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#60 ·
Actually the Bio Rio that Amano uses is REALLY good at capturing debris, even the silt when aquasoil is stirred up. I replaced all my media with Bio Rio for that reason. It compacts and catches a lot of debris but does slow down the flow a bit.

I only use Bio Rio (and purigen on top) in my ecco. I do have a coarse filter pad on bottom but that is only so the bio rio doesn't fall through the bottom tray (it's pretty small.)
 
#61 · (Edited)
I found some old pictures of one of my first high tech planted tanks. I have talked about that tank - the one with the extremely healthy Java Fern in it. The picture of Java Fern that you have probably seen somewhere on thenet came from that same tank. The plant is not Photoshopped at all. The background is made blacker than it actually was, that's it:



On this picture you can make out the spraybar in the back:


So on the pictures I just found something pretty amuzing. The tank was basically a Gyre indeed! The very thing we discussed here few weeks ago. The water flowed out of the spraybar that was placed on the bottom, at the back glass. From there the water moved forward under the Java Fern roots. Then the water went up and to the side to the intake.

Besides the Java Fern the tank had only very short hairgrass that barely grew because the Fluorite substrate was new. There were also two Crypts which also barely grew. So nothing blocked the good flow pattern.

As I said - that was a 4' long 55 gal. standard tank. When I pulled the Java Fern out of it I laid it on a 6' long table and it stretched from one to the other side. A strip of Java Fern 6' long and 8"thick! Every leaf was completely healthy too.

Since I have very much posted all the above information already in this or other threads here's the new and strange part - the flow on that tank was very little. Smallest Hydor canister filter. Something like 160 gph. Add the hydrostatic head, the 90 degree elbows for the spraybar.. and I bet the flow was something like 50 gph if so.

So I believe that the open layout of the tank allowed for very good flow pattern and almost 10 years later I think I have it figured out.

--Nikolay
 
#62 ·
This has been a find... Especially the illustrations of flow, grye, and the u shapes. They have really hit home. I recently made a mistake in the hardware arrangements on a long low tank (a GLA 91-B) than I think has an incorrect flow pattern. I hand bent some acrylic tubing to make a spray bar flush to the right end the tank with a spread pattern aiming toward the left. I built an intake with acrylic on the left hand side of the tank in the rear. I then hooked up an old monster 404 fluval to the pile and just prayed I wouldn't blast the substrate off the bottom. I figured that the filtration would flow smoothly from one side to another and the tank would have distinct flow patterns. Instead it stalls out and has built up a pile of protein scum on the left side surface that I wouldn't have expected. Even with the slightly unusual dimension's of such a flat tank I am now thinking I will be much better served with the Amano style setup. Any thoughts before I go thru the work of re-engineering the the stand and the acrylic?
 
#63 ·
Best thing to try that anyone can suggest at this point is to emulate ADA's placement of the pipes. That's the best starting point.

In the past I have tried huge flows and was always surprised to see that they did not take care of all the trash in the tank. I always assumed that with a lot of flow you can clean anything. That is not so. Flow pattern is REALLY important. It's somewhat amusing that we are starting to understand that just now.

--Nikolay
 
#65 ·
Best thing to try that anyone can suggest at this point is to emulate ADA's placement of the pipes. That's the best starting point.

In the past I have tried huge flows and was always surprised to see that they did not take care of all the trash in the tank. I always assumed that with a lot of flow you can clean anything. That is not so. Flow pattern is REALLY important. It's some what amusing that we are starting to understand that just now.

--Nikolay
Sorry to burst your bubble but of all my equipment I own a single powerhead and never purchased a flow accessory besides eheim plastic and ada style glass. Besides the fancy verbage I am trying hard to find the incredible breakthrough here. Thanks for breaking it down for the rest of us.
 
#66 ·
Brilliant,

If you think you have something uselful to say can you please retype the first sentence of what you just said because it makes no sense.

This time do not start with "sorry to burst your bubble". It is a cheap insult and you know it.

I'm interested in the rest of the sentence and your experience. And note - I'm not confrontational.

--Nikolay
 
#67 ·
Brilliant,

If you think you have something uselful to say can you please retype the first sentence of what you just said because it makes no sense.

This time do not start with "sorry to burst your bubble". It is a cheap insult and you know it.

I'm interested in the rest of the sentence and your experience. And note - I'm not confrontational.

--Nikolay
Apparently you were able to comprehend.

Now kindly explain in laymens terms what we have all been in the dark about for years. Ive read through the pages and can only see that elaborate flow setups are not as useful as imagined and single output is more effective. Am I missing something? If so I am interested in understanding what the big deal is all about. Thats all.
 
#68 · (Edited)
How enlightening! I've been having some major issues with particulate matter in my new set-up, the 125 I got from mudboots. I recall him having the same issues when he had it.

I've got a canister filter and 2 powerheads (Koralia II and off-brand) and I thought I was getting the right movement. After reading this thread, I looked carefully and sure enough, particles were just floating all over the place, never settling, never making it to the canister intake.

I just now removed both powerheads and placed the canister filter output/intake at the end of the end of the tank as described for ADA stuff. I don't see the circular motion from top to bottom, but I do see it from front (water going forward) to back (water returning to intake). Probably I won't see the "Lily Pipe" motion because I don't have lily pipes, but it will be interesting to see in the next couple days if this helps with the particulate issue. (I'll let you know. )

I need to find the data on that filter so I know what ghp I'm looking at. My guess is that it is very low.
HERE it is. It says it pumps 250 gph.
 
#71 ·
If you typed something insulting your post would have been deleted by the moderators. You should see what I wrote in a new post 3 days ago about the ADA contest judging and expectations. My post disappeared within 1 hour.

Here. Let's be constructive;

Brilliant, could you write your thoughts on filtration? Simple and clear.

I will not come back with some half-baked witty remarks. Or any remarks that are negative. That will kill this thread.

--Nikolay
 
#72 ·
You have to understand I was under the assumption planted tank people were experienced aquarists. I never really thought someone would be starting the aquarium hobby with a planted tank right off the bat. You will have to forgive me for thinking we were all from the same heritage. You know golfish bowls or tanks with background, fake ornaments and colored gravel.

Filtration is very simple.

Buy Eheim
Dont over-engineer your flow config
Use oem or buy fancy glass pieces


My intake has always been in the corner to be visually pleasing more than anything. It just so happens that thats an ideal place to locate the intake.

The output flow should roll the tank. I remember messing with my output years back now I always put it on the side of the tank. Its visually pleasing and more effective. I even put aquaclears on the side.

Ive added a koralia to provide more flow once in an attempt to increase co2 throughout the tank.

The planted tank in itself is a filter. I dont really know how to explain how it works but let the natural filter do its job. Large water changes and man made filtration is counterproductive to the natural filter.
 
#73 · (Edited)
So the title of this post caught my interest, as I just graduated aerospace engineering and want to find *some* way to apply my shiny new degree :) Reading this post, I'm realizing how little I remember from the past four years.

I had a couple questions, though. Reading through the posts, I wasn't sure if there was the underlying assumption that either laminar or turbulent flow was better for the tank, or if that point itself was what was being discussed. If one or the other is better, could someone explain why that is? Is it in general better to have suspended particles, particles in the gravel, or do you want those particles filtered out? I assume that you would want the dissolved nutrients evenly distributed throughout the tank.

A couple posts caught my attention. One subtle distinction (not sure if it matters) is that a flow goes turbulent once a flow has achieved a high reynolds number (Re), but the turbulent flow itself doesn't have a high Re. There is no corresponding descriptor for turbulent flow, actually. Also, one thing that wasn't discussed (I don't think...sorry if it was) was the property of turbulent flow to "stick" to a surface better than a laminar flow. It's for this reason that airfoil designers sometimes actually want turbulent flow in some regions of an airfoil. This property might be relevant in considering the flow past leaves. The flow is much more likely to separate from the surface of a leaf if it is laminar. Another property to consider is that turbulent flow is an inherently chaotic process. This means that something like cigarette smoke is not (usually) a turbulent flow in the technical sense, though in the colloquial sense of "turbulent" it might be described as such. With regards to the coral vs plant discussion, if I understand correctly, coral is a colony of tiny polyps. Because they're a colony, they have no central means of distribution like a plant does. Thus, each polyp must have all its nutrients flow past it, whereas a plant uptakes many of its nutrients through its roots (but not CO2, I believe). That would extend the discussion to what would provide good flow through the gravel. Another distinction that just came to mind was turbulent flow in general versus in the boundary layer. The boundary layer (region close to a surface) of a laminar flow is turbulent due to the imperfections of the surface. The thickness of the boundary layer is dependent partially on Re.

Phew...sorry if that wasn't useful, but it felt good to try to remember what I know. I'm about to start my first planted tank after five years of lurking but never having enough time to start a tank. Maybe I'll get to experiment with some flow properties!
 
#74 ·
#76 ·
#77 ·
@Ekrindul
That was a fascinating read! They focused on phosphate and ammonia - I wonder if their results hold true for trace nutrients.

@digital_gods
I think we're using two different definitions of boundary layer. If I understand it correctly, you're using it to describe the boundary between air and water, whereas I'm using it in the fluid dynamics sense - as the boundary between a fluid and a solid. With air, at least, when you have a flow past a solid surface, the boundary layer is referring to the thin layer of air between the main airstream and the solid surface. The properties of that layer of air can be radically different than the properties of the surrounding air.
 
#78 ·
@Ekrindul
That was a fascinating read! They focused on phosphate and ammonia - I wonder if their results hold true for trace nutrients.
Unfortunately, much of the small amount of research there seems to be available on the subject isn't freely available. Hopefully, Phil will see this and enlighten us.

I've read that the bulk of nutrients in aquatic plants were collected by the root system, and also that the bulk of nutrients were collected by the leaves. I've read that the roots primarily function to collect carbon and anchor the plant. I seem to recall reading somewhere that iron transport in water hyacinth from root to leaf can take a few weeks to accumulate to a significant amount (would certainly point to an advantage for a plant that could collect iron from its leaves).

Seeing as plants cannot move when things aren't going well, it would seem reasonable that they would have evolved to have options.
 
#79 ·
I just read this entire post and it is very fascinating. It might be just me but I find designing a flow pattern to be mostly common sense. Just keep it simple, and it will be effective. Take powerheads for example, I personally feel that there is no place for them in most freshwater tanks, especially planted ones, unless you are running no filter and need it for singular movement.

Think about the natural environment. In a marine environment there is a LOT of turbulence around reefs cause by the water going rapidly from deep to shallow, e.g. waves. With the extremely large volume of a wave there is a lot of pushing and pulling of water in every direction. That's why reefers use so many powerheads pointed in every which direction and wavemakers on top of the outflow from the sump. They are attempting to emulate the corals natural environment on a generally very turbulent reef.

Now look at the typical freshwater plants natural environment. The current almost always flows in a fairly uniform direction, at a uniform speed. Typically there are no harsh cross currents or highly turbulent areas where these plants grow. If you think about a freshwater system, spring to end-point, it seems to me like a giant never ending train, one big continuous cycle. By the way I live in the most lake populous state (stick a sock in it Minnesota) so looking at a map I can see more lakes and river systems than I can count. Anyways what I'm trying to say is typically there is only one directions of water movement, forward. All there is, is where its coming from and where its going. Inflow and outflow. In this context it is easier to imagine the plants natural environment as a closed system and relate it to our own.

What you want, as has been previously mentioned, is one flow, in a loop, with inflow and outflow near the same point. This is as close to a magic formula as you are going to get, unless you want to build the same tank every time, and there is not fun in that. The rest of the details such as direction, flow rate and location are personal to your individual tank and are easily worked out on set up. Just observe and adjust. There are generally plenty of bubbles and other crap floating around in the water, just start with a high flow rate, find your location, find your direction, adjust your flow rate and your done. I feel that this is as close to the natural system as we aquarists can reasonably achieve, and it shouldn't take you 10 minutes. I usually find myself aiming the flow down the largest dimension of open water.

On the subject of laminar vs. turbulent flow, sometimes I find it is hard to have one and not the other. Take my 55 long for example. I was found it was difficult to get uniform flow and total tank coverage due to the length. What I ended up doing was taking the spray nozzle and aiming it directly across the middle of the tank. It was about 3 inch below the surface and blowing parallel to the water line. Once I adjusted the flow rate, it was perfect for my tank! The flow near the surface was of course a pretty turbulent but only a little past half way. When the water hit the other side it slowed a bit and formed a strong undercurrent that when to the bottom and then back across to complete the cycle. And wouldn't you know it, after the turbulence spread out I had perfect, even flow throughout the rest of my tank. The upper-left was turbulent, but the upper-right, bottom-right, and bottom-left were laminar. I also had no dead spots. Like I said though, this was perfect for MY tank. The tallest hardscape was maybe 7 inches and the tallest plants were probably 12, so they were unaffected by the turbulent top few inches, and my dannios loved the turbulent section. They'd sit there a swim head on into the outflow like it was nobodies business.

I love this thread and can't wait to read more on this.
 
#81 ·
I actually read (ok...skimmed) a few interesting articles after my interest was piqued.

Effect of boundary layer transport on the fixation of carbon by the giant kelp Macrocystis pyrifera
I couldn't find this one in the databases, but I'll try again tomorrow. The abstract contained this interesting statement, though:
"Experiments in water tunnels indicate that the boundary layer adjacent to the M. pyrifera blade may be turbulent in water speeds as low as 1 cm sec-1. Photosynthetic output of the blade can be increased by a factor of 300% by increasing water speeds over the blade surface from 0 to 4 cm sec-1. This is consistent with a decrease in the thickness of the boundary layer. Above 4 cm sec-1, the assimilation of carbon was limiting."
Velocity gradients and turbulence around macrophyte stands in streams
http://www.mediafire.com/?a9dvlukzg7czwbn
Turbulence was maintained in the attenuated flow inside the plant canopies, despite estimates of low Reynolds numbers, demonstrating that reliable evaluation of flow patterns requires direct measurements.
You can't trust your intuition as to if it's laminar or turbulent - you have to measure the flows. This article talked about how the plant beds alter the flow. The flows can become more OR less turbulent depending on plant bed characteristics.

Beyond light: physical, geological, and geochemical parameters as possible submersed aquatic vegetation habitat requirements
http://www.mediafire.com/?bzw1tng221vgjag
This had a TON of awesome information. For example:
Production of turbulence within the vegetation is dominated by the plant wake rather than by the bottom boundary shear, as in open channel flows (Nepf et al. 1997).
meaning that in streams and rivers, the turbulence is caused by the shear forces with the channel bed, whereas it was caused by the plants themselves in lakes (where the flow is due to wind driven waves). Also:
The optimal turbulence levels for SAV is yet unknown but it is interesting to note that most SAV beds tend to occur in areas where flow is characterized by the laminar-turbulent transition (Ackerman 1998)
meaning it might be best for the flow to start out laminar but transition to turbulent as it hits the plants! There's a lot more to dig out in this paper, but I don't have time to read the whole thing. Someone please post any more interesting bits if you have a chance to read more.
 
#83 ·
I'm writing this in an effort to remember it by re-wording. My learning effort maybe useful to someone else. Here it is:

--------------------------------------------------------------------------------------------------------------

First off, what is a "Boundary Layer"?

Google:
Boundary layer: The layer of fluid that sticks to a solid surface and through which the speed of the fluid decreases.

RedFishBlueFish's quotes say that:

- I cannot maintain only laminar flow in an aquarium.
- I do not need to maintain laminar-only flow in a planted tank.
- It is best to have a transition - the flow starts as laminar and turns into turbulent.
- There is optimal flow. It is a range (not a specific number). The range is 0 to 4 (some units)
- Within that range the plants can seriously increase their growth. (0 - 300%)
- Flow that is too fast can actually stop a plant's growth.

All of the above statements have to do with this "Boundary Layer" thing. But the only thing I can adjust are the pumps. All I can do is increase, reduce, and direct the flow.

--------------------------------------------------------------------------------------------------------------

My smartest approach for now is to find videos of tanks that show healthy growth and no algae. And watch for the flow in these tanks - speed and direction. So far I've noticed that ADA's tanks often (but not always) seem to have many plant leaves gently moving from strong flow. From what I read above it looks like it is pretty hard to say if a flow is laminar of turbulent just by looking. I also think that it is hard to say how strong a flow is by just looking. Especially on videos. But once again - it appears that if I make the leaves of my plants gently move in the current I am doing something in the right direction. And there is more to be done. Hopefully with this and other disussions we can find it.

And I will not be surprised at all if the general conclusion on what is optimal flow speed & direction in a planted tank are not far from what Brilliant said above - "very simple".

--Nikolay
 
#84 ·
RedFishblueFish,

From the quote below you conclude that is is best to have a transitional flow in a planted tank. A flow that starts as Laminar and turns into Turbulent.

What is "SAV" here?

"The optimal turbulence levels for SAV is yet unknown but it is interesting to note that most SAV beds tend to occur in areas where flow is characterized by the laminar-turbulent transition (Ackerman 199...)"

--Nikolay
 
#86 ·
Here's a cheap (actually costing nothing) hack to achieve a resemblance of a laminar flow:

1. Install and HOB filter on the tank. Best placement - on the left or right side glass. Run it as normal.
2. Setup a second filter - a canister filter. Place the outflow pipe in the HOB filter box. (Place the pipe in front of whatever filter bag is used by the HOB filter.) Place the intake on the same glass on which the HOB filter is hanging.

That's it.

You get a very pronounced U-shaped flow with the HOB anyway. Adding the canister filter flow to it only helps. And it does not counteract the main U-shaped flow in any way.

A predictable thing that you will notice is that your 80gph HOB filter moves more water than the 160 gph canister filter. The main water movement is from the HOB filter. Good thing to remember when looking at flow rate of canister filters - most of them don't even come close to what is written in the box.
 
#88 ·
Here's a cheap (actually costing nothing) hack to achieve a resemblance of a laminar flow:

1. Install and HOB filter on the tank. Best placement - on the left or right side glass. Run it as normal.
2. Setup a second filter - a canister filter. Place the outflow pipe in the HOB filter box. (Place the pipe in front of whatever filter bag is used by the HOB filter.) Place the intake on the same glass on which the HOB filter is hanging.
I've had about 45 days of observations with that kind of setup. It's a 30 gallon tank at my church. The canister is an Eheim.

The tank has no plants. Just 3 small fish and funky blue color gravel (tank is in the kids area). With a once a week 30% water change there no algae developing on the glass or equipment. One place always develops algae - brown dust looking algae develops on the gravel only (no tuffs or strings). The light is only a 15 watt fluorescent which I will soon replace with a T5HO.
 
#87 ·
Re: Discussion of laminar vs turbulant flow - Experiment

Hello everyone

I have been reading this old thread with interest. Right now I am trying to establish a slow, unidirectional, laminar flow from one side of my 400L tank to the other using a manifold design, similar to the hillstream approach but with a submersible Eheim pump instead of powerheads. And with a gentler flow rate.

My plan is to use a series of eheim spraybars attached via u-bends into a kind of grid. I have no idea if this will work :) It will not be elegant! It will have many a green pipe and black suction cup! But hopefully I can conceal it with some roots and rockery.

The overall intent is to emulate a coastal stream in Cameroon complete with appropriate fish, inverts, and plants. The streams are neither rapids, nor sluggish. Can it be done? Stay tuned...
 
#89 ·
Today I got around to hooking up the second big external Eheim pump to my 2 canister filters in a 180 gallon tank. I have the outflow hoses from the canisters plugged into a larger diameter U-shaped acrylic pipes (normally used for overflow boxes).

The flow coming out of the U-shaped pipes does look as close to laminar as it could be with such a setup. The water coming out of the U-pipe looks like acrylic itself - a completely silent smooth pillar of water. Except that is shoots straight down. I'm headed to Home Depot now to find a metal spring and try to heat and bend the end of the U-shaped pipe to an L-shape. Hopefully this will keep the "laminar" flow.

I attached a 90 degree PVC elbow to the end of one of the U-pipes. The water flow shoots out in a chaotic stream and makes a noise. Certainly far from laminar.

I am not hellbent on this laminar flow. I believe that as long as the water in the entire tank moves well you are good to go. The smoother the movement the better because then the water acts as a single body and could pull debries better - that's hard to deny.
 
#90 ·
Good discussion on flow patterns.

I have a quick question for those who have looked at the flow patterns extensively. I currently have my lily pipe outflow on the front left corner and the intake on the rear left corner. Would it be worth drilling another hole in the stand to move the intake next to the out flow on the front corner?

Thanks for your thoughts.
 
#91 ·
Allrighs so I did the DIY acrylic bending and ended up with two U-shaped pipes with each end of each pipe pointing along the surface of the water. Think if it as a lily pipe without the lily.

The flow is very smooth. Not as smooth as coming out of the U-shaped pipe without the additional bent but I guess that is as close as it can get to smooth. Now I have 1000 gph actual flow in a 180 gallon tank. The tank is actually 160 gallons without decoration but Oceanic calls it a 180. So my flow is 6 times the tank volume per hour.

Both acrylic outflows are placed on the left side of the tank and close to the front glass. The tank has been drilled for 2 intakes on the bottom - in the left and right corner. I'm not going to change that for now.

UltraBlue,

The way ADA sets the flow pattern is both by the placement of the ouflow and the inflow. Look here:


The red arrows are the water flow along the front glass only. Someone did an experiment with suspended particles added to an ADA tank and they found that there is a U-shaped flow on the surface of the water too. In the current thread we have very much accepted that this double U-shape of the water flow engages water from the back of the tank too IF the current is smooth AND strong enough. The flow is both smooth and strong in an ADA tank. Placing the outflow and the inflow close has a synergistic effect (it multiplies the result without adding any extra effort) - it creates the strongest possible smooth U-shaped flow along the area that is normally free of plants and decorations - the front glass.

The essense of this thread is how to get the water flow smooth because this is a logical conclusion if you watch how the debries are being moved from all parts of the tank toward the intake. A chaotic flow does not engage the debries in a directional movement. And once again - the flow must be both smooth and strong.

Note also the yellow dots with short arrows on the picture above. These are debries that need to be moved toward the intake. Because the ADA intake is placed a little above the substrate there is a slight upward movement of the water along the bottom. This "pulls" particles out of the surface of the substrate and lets them engage in the flow toward the intake. Except that from what I can say now observing a tank without plants only the tiniest particles can be moved upwards that way. I now believe that Amano shrimp have the role of "shaking up" the larger particles, dislodging them from the susbtrate and make them suspended. Amano shrimp are pretty rough little animals and you can often see that they raise small bursts of dirt around them.

And to answer your question: You don't need to change everything in your tank to match ADA's setup. ADA has taken old knowledge and presented it in a cool and modern way. But that does not mean that you have to do everything exactly as ADA does it. As long as you engage the water from all over your tank in a smooth flowing movement you should be good. And if you are not - see if you flow rate is enough, see if dense plant tuffs keep the water from flowing good. Move the intake a little here and there before you install it like ADA suggests. It is hard to beat what ADA does but if you understand why they do things you can tweak them any way you like.
 
#92 ·
This isn't a perfect gyre, but moving the spray bar to the side accomplished a nice u-shaped flow in my tank. I made this change long ago after the discussion here.

In this video, I drop some small, sinking pellets into the tanks. You can see then move left->right, bounce off the right side and down and right->left.

It doesn't really show up well in this phone video, but I tried to follow some of the particles along the bottom of the tank back towards the intake side.

Not the double-U that a lily pipe can make, but better than a front-to-back arrangement.

 
#93 ·
I have a mini-m and a superjet ES-600 (After owning one, I love the superjets!) even though the filter is only about 100 gph, the flow was way too intense with a mini lily pipe. I switched to an off-brand lily pipe to decrease the flow, but it still moves the aquasoil on the opposite end of the tank.


If just ordered a 45-P since I wanted to upgrade anyway. If the flow is still too strong, I am considering being a guinea pig and ordering the new lily pipe spin, which is a circular pipe that releases water on both sides. It looks like a tire.

I was wondering how this would positively or negatively affect the flow. It can't be bad if ADA releases it. OTOH, maybe flow doesn't matter that much on small tanks when you are using superjets?

I could order the new superjet es-300, but I can't justify spending $400 or so bucks when my es-600 holds six liters of media and the es-300 holds three and is only 50 GPH.

I am hesitent to use a tap connector to decrease the flow..would it negatively affect the Iwaki pump?
 
#94 ·
Hey y'all,

Niko and I had a really stimulating talk the other day about flow regimes in planted aquaria and it got me thinking. His example of laminar flow in the San Marcos in a previous post is awesome and I thought I'd expand on it a little. After keeping planted tanks by rote for so long, having a deeper understanding of the science behind what's going on in my aquaria has helped me immesurably. I thought I'd talk a little bit about what I've learned in the hopes it'll increase your understanding of your aquaria and improve your hobby just as it has mine.

Reynold's number (Re) http://en.wikipedia.org/wiki/Reynolds_number

The initial statement "...such as laminar or turbulent flow: laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion, while turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities." contains the critical element' smooth, constand fluid motion vs. chaotic and other flow instabilities.

Going back to the San Marcos and other plant-filled streams many of us have seen; the flow in such streams is for the most part laminar. It may not be purely unidirectional and constant throughout the water column; however overall the stream flow isn't chaotic. Considering channel morphology; such streams are characterized by a general broad U shape. This is important! Although discharge may be high, the open nature of the channel allows for high flow with little impediment. Such flow regimes are beneficial to aquatic vegetation for multiple reasons:

1) Low shear forces- Although shear stress is present in all natural fluid flow situations; eddies and other turblent flow instabilities are areas of high localized shear stresses. We see this in our aquariums when using spray bars. The flow nearest the outlet is very fast relative to the area around it. This differential velocity creates eddies and vortexes in which shear forces can cause plants to lift out of the substrate or which can tear leaves off the stem; thereby damaging the plant.

2) Chaotic flow (high Re) likewise creates zones of increased and decreased water movement. We see this characterized by zones of deposition and resuspension of mulm in our tanks. The zones of high flow receive good input of nutrients and CO2; whereas the zones with low flow may be deficient in one or the other. Likewise, the deposition of mulm can create zones of localized water quality instability and become a source of harmful chemicals.

Consider the placement of filter outputs for a moment. The convention of placing the filter outflow on the side of the aquarium rather than the back aids in the creation of laminar flow. Why? The increased length of flow helps to disperse the energy related to filter discharge. The farther the stream travels before hitting an impediment such as the side of the tank, the greater the impact viscosity plays in the flow dynamics. Conversely, if I put a spraybar or other outflow on the rear of the tank facing the front, the short distance between the initial outlet and impediment decreases the contribution of viscosity which causes an increase in energy when the flow hits the impediment. The higher the flow energy at point of impediment, the greater the Reynold's number, and the greater the turbulence of flow at the point of impact.
Using the below equation we see the following:



Given a constant viscosity, discharge velocity, and density of water leaving our filters; L, distance to impediment or width of stream flow is the characteristic which defines flow regime. If L is small, Re will be large. If L is large, Re will be small. Remember, we're multiplying L by two constants and dividing by another constant. The greater the pVL term the lower the overall ratio.

What the hell does this mean for my aquarium? In order to create an environment with the greatest potential for laminar flow we must set up a situation where either L is high or V (discharge velocity) is low. To use my aquarium as an example. I have spraybars placed along the substrate surface and tank sides which face the front of the tank (small L). In order to maximize laminar flow potential I have to decrease V. Assuming my pump is always discharging at a constant rate and the viscosity and density of the water leaving the spray bars is constant, I must either increase the size of the holes in the bar, increase the number of points of discharge, or both in order to reduce the Re.

Why would I care about that? Don't I want the highest velocity possible from my spraybar to suspend mulm so it can be picked up by the filter or transport it to a place where I can syphon it out? No!!!!!!! Remember, high V creates turbulent flow which, in turn, creates flow instabilities as discussed above. I want smooth, laminar flow to uniformly distribute water. This uniform flow distribution may be slower than turbulent distribution, but it is more effective in both nutrient distribution and removal of undesireable materials from the water column over the long term. Why?! Because laminar flow reduces differential zones of suspension and deposition. The greater the proportion of zones of suspension to deposition, the greater the volume of particles removed from the water column OVER TIME. This is the big secret and science behind the Lily Pipe and convention of placing the filter outlet on the side, rather than back, of the aquarium. Since stability is, by definition, a characteristic of change over time, one must consider efficacy over time rather than instantaneous or immediate efficacy. Turbulent flow can improve results in the short term, that's why we stir the water in planted areas at times when cleaning our aquaria. The instantaneous turbulence suspends the particles we want to remove. In general, however, this is not a desireable condition.

Im a commercial photographer that specialises in liquids, far from academic, but find liquids fascinating to film and shoot. new on the site and not totally shaw where to ask this question? I have a fascinating shoot on where I need to create a very even on mass flow of water from the left side of the tank to the right. Im attempting to build a tall and wide laminar flow, so that the water form the pump in from the left is moving about 4 litres a second but is smooth, no vortexing. Reason for this is there are objects that are designed to move in very specific ways in water, so a even flow is essential to monitor the precise movement.

Ill upload the design, build... Its a test. used a simple laminar flow jet before, but this is moving water on mass from the left to the right of a large tank and being sucked out from he right, and around it goes..

Any ideas - suggestions, very welcome. If your curious about my work, its www.davidlund.co.uk

Thanks for your time. I should be filming some Behind The Scenes which I can share.

David
 
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