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Discussion Starter · #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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Honestly, the more I think about having the water move in a laminar pattern the more I think we maybe on to something.

The idea is to involve as many waste particles in the water movement. A laminar flow does seem to literally pull particles off the bottom and from any surface. Shrimp and otocinclus can only help suspend them.

I really liked that you make a serious point of the difference in the short and long term. I do not know if our ideas about laminar flow having more "cleaning power" are really true. But definitely the results will be seen in the long term.

Also the fact that with laminar flow we may not need pump to move 8-10 times the tank volume per hour. ADA's filter for the 180 gallon tank is moving only 3 times the tank volume an hour! How can that be the standard filter suggested by ADA? You are telling me that in my 180 gallon tank I can put a 460 gph pump and filter it fine? No way! Except maybe if the flow was laminar... Or if the tank was a very open aquascape with only carpet plants.

http://www.adana.com.my/products/filter_system.htm

This is getting exciting (despite the formulas) :D.

--Nikolay
 

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Discussion Starter · #3 · (Edited)
LOL, just wait until I post a discussion of shear forces. :confused::confused::confused::confused::confused: :tape2::tape2::tape2: :rolleyes::rolleyes::rolleyes:


Don't forget Niko, the information you've found is mostly in reference to aquaculture where the goal is to produce as much fish mass in the smallest volume possible. That requires A LOT more filtration than does a decorative aquarium. It's still very good and useful information, we just have to take it in the context of our aquariums rather than a grossly overstocked system.
 

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Some problems that keep bugging me I wonder if you could address, Phil.

How could we apply laminar flow to a rectangular aquarium where the outflow is so narrow and where the water must circulate rather than continue along a unidirectional path? Even with a spraybar, we cannot recreate the effect seen in a river where the flow is uniform. If we attempted to create laminar flow using either a spraybar or powerhead by extending the flow as far as possible before an impendment is reached, won't we always be creating the largest deadspot above or below the outflow?
 

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This discussion reminds me of river tank manifolds used by hillstream loach keepers.

I can also add from practical experience designing water features that the easiest way to decrease turbulence and increase laminar flow in piped systems is to increase the diameter of all the pipe. Aquarium circulation/filtration is designed with the smallest possible pipe--easier to conceal. But these small pipes increase turbulence, especially when the water is squirted back into the aquarium through a small-diameter opening.
 

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Discussion Starter · #6 ·
Some problems that keep bugging me I wonder if you could address, Phil.

How could we apply laminar flow to a rectangular aquarium where the outflow is so narrow and where the water must circulate rather than continue along a unidirectional path? Even with a spraybar, we cannot recreate the effect seen in a river where the flow is uniform. If we attempted to create laminar flow using either a spraybar or powerhead by extending the flow as far as possible before an impendment is reached, won't we always be creating the largest deadspot above or below the outflow?
Laminar flow doesn't mean unidirectional flow.

The definition of laminar flow is dependent on the kinetics and energetic state of the fluid. Up to a certain energetic state the viscous and kinetic properties of water resist turbulence; this is Laminar (not unidirectional) flow. As soon as the energetic state of the fluid goes above a threshold defined by the viscous and kinetic properties of that fluid, the flow becomes turbulent.

Likewise, flow in rivers is not uniform. The area of highest flow is somewhere in the middle of the channel whereas the lowest flow is along the banks and bed. The solid structures of the bank and bed create friction which reduces flow velocity (topic for another upcoming thread). A stream will have places where the flow is generally laminar and areas where flow is generally turbulent. However, even in an area that is generally laminar as defined by an appropriate Reynold's number there will be zones of turbulent flow due to the influence of friction and shear forces.

Remember, water flow is always in three dimensions except in insane theoretical circumstances. Even though the water in our tanks may be jetting out of a spraybar, the viscous properties of water will cause water from behind, above, and below the outlet to move toward the direction of strongest flow. *This is where lily pipes come into their own* They're designed in such a way as to maximize flow congruency in areas surrounding the outlet. In effect, the design of the structure maximizes the tendency of moving water to pull the surrounding water into the stream. Korallias and similar products, as well as penductors/eductors, capitalize on these kinetic and viscous properties to create mixing around the outlet.

This effect is reduced when using a spraybar as there are multiple outlets.

If you've ever put a floating toy on the water and caused it to move by dragging a finger through the water ahead of it; you've seen this principle in action.

Michael hit the nail on the head. Since we're pushing water through the smallest possible outlet we're increasing the velocity of water discharging from the outlet. If discharge (velocity times area) is constant, decreasing the area of the outlet increases velocity. That increased velocity is a result of concentrating the kinetic energy of the water as it passes through a compressed area.

Conversely, increasing the are of your outlet decreases the velocity and kinetic energy of the stream as it widens and the energy is diffused through a broader area. If we wanted to maximize the potential for creating laminar flow (it's in 3 dimensions, remember) we would have to create some sort of outlet structure which reduces outflow velocity enough to achieve a kinetic state which is below the threshold of turbulent flow.

This structure is also known as a Lily Pipe. ;) The more I think about all this stuff, the more I realize ADA has put some SERIOUS time and money into R+D and have paid a lot of energy into understanding topics such as fluid dynamics and engineering design as opposed to solely design/aesthetics.
 

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Discussion Starter · #7 ·
Cool visual of laminar then turbulent flow.


Low Reynold's flow (laminar) through a tight opening (aka spraybar). See how flow compression causes turbulence.


Demonstration of 3D water "pulling" from a lily pipe. The vortex is created by slower moving water being pulled into the faster moving stream leaving the lily pipe.


A great video demonstrating the same with riccia:
 

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Demonstration of 3D water "pulling" from a lily pipe. The vortex is created by slower moving water being pulled into the faster moving stream leaving the lily pipe.


A great video demonstrating the same with riccia:
Yes, I see the same effect with my Koralias, but never with say a Hagen powerhead.
 

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This discussion may seem pretty hard to read or even useless to someone. But I assure you - this, and a few other topics published here in the last several days, are things that we should have known 10 years ago. It would have propelled this hobby to a new level back then. At least something is moving now. So please check these posts when they are updated. The information found here cannot be found anywhere else. And it will probably change a lot in the way we setup planted tanks. This is only the beginning of something new. It will take a long time to establish itself.

So, to give you a simple visual impression of why we started discussing water flow rates and flow types I will remind you that most of us intuitively believe that the more flow you have the better you are removing the dirt from your tank. We also believe that the more jets you have scattered around the tank the better - they all move the water from a gazillion angles and the dirt has no place to hide. We have all seen (and some of us designed and used) elaborate manifolds placed under the gravel, Koralias all over, spraybars in every position imagineable and so on.






On the other hand ADA uses a very simple and elegant solution. Sorry for the repetition, we have all seen a Lily pipe, but here it is - the same thing every single time:


So it is logical to wonder what is it that ADA knows and does that we, as a community, don't.

By closely looking at the operation the Lily pipe a few things jumped out. That is what is discussed in this and the other recent threads about filtration.

This post is meant to give you a visual impression of why we discuss these topics. Here's another visual - this time maybe hitting close to home. I believe many of us can literally look at their tank(s) right now and see what I'm talking about:

Yesterday I did a water change in my big tank and scrubbed a little alage from the Manzanita wood. Fine dust from the soft Manzanita blew everywhere, but I did not think much of it.

Today, a day later, I looked at the completely clear water in the tank. Yes the water is perfectly clear but there were still suspended particles of the Manzanita floating everywhere. In my effort to see if these are microbubbles of air or actual Manzanita dust I observed the particles for some time. I noticed that:

1. The particles were brown (so they were.. and are... wood)
2. The particles never settle! They dance around inside invisible boundaries! Endless suspension! I tracked one bigger particle and I saw that it moved around inside an area measuring about 10 sq. inches. It never settled, it never went to the filter, it just kept moving around. Along with thousands if it's finer siblings.

In that 180 ga. tank I have 3 Koralias, 2 filter outflows, and a HOB micron filter. Flow is about 1800 actual gph. But they are not enough to move all the particles into the filter. On the other hand they provide the tiny particles with opprtunities to be ground down to waste having an immense surface area. Wow!

Look at your tank. If you notice suspended particles that just dance around and never go anywhere you need to continue reading the posts about filtration and laminar flow. What you have is a nice factory for organics, waste and ever growing surface area of the trash you are recirculating and tumbling around.

Many people that have nice clean tanks will say that they are just fine with the water movement setup they have. But that doesn't mean that things cannot be streamlined and improved. ADA uses only about 450 gph of flow in their 180 gal. tanks. Try that with a nice big Eheim filter and you will fail. ADA has success with such a setup because they do things differently than what we know and believe.

Keep reading. Please.

--Nikolay
 

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Phil, I leave you on your own here. Niko has left the building.

Some New Jersey or something guy in another thread got to me. Hope he doesn't respond to what I posted or PM me.

Right now I could care less if anyone is interested in knowing more about this hobby.

From now on my post will be as exciting as this:



--Nikolay
 

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Why wouldn't an Eheim filter with a flow of about 450 gph on a 180 gallon tank with a lily pipe outflow work just as well as the Superjet filters? I don't see how you will fail just because you aren't using the ADA brand filter, which costs a fortune.

This is a very interesting thread and I will be re-reading it later. Very interesting ideas. I really see what you are saying about how laminar flow drags or pulls the particles.
 

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Why wouldn't an Eheim filter with a flow of about 450 gph on a 180 gallon tank with a lily pipe outflow work just as well as the Superjet filters? I don't see how you will fail just because you aren't using the ADA brand filter, which costs a fortune.

This is a very interesting thread and I will be re-reading it later. Very interesting ideas. I really see what you are saying about how laminar flow drags or pulls the particles.
I think what Niko is saying about the SuperJet filters is that they don't lose gph as easily because they are rated for more power. In other words, the Iwaki pumps that are installed on top have a higher maximum head.

So if x brand of filter is rated at 450 gph with a maximum head of 8 ft and the y brand of filter is rated at 450 gph with a maximum head of 20 ft. the y brand filter will maintain it's near maximum flow for a longer period of time because it can overcome the clogging that occurs over time.

Think of it in terms of cars. If two cars have the same horsepower, but one has more torque, the one with more torque will still be able to accelerate at nearly the same rate even if some more weight is added to the car.
 

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@Niko - you must come back in. You got me with post #9. I have been reading the two threads eagerly. I have seen the ever floating dust in some tanks. I need to really take a look at my loops and make sure that I have them also as "closed loop" inside my tank. It makes a lot of sense that not only may we need to think about dead areas as having no flow but also as dead areas with ever perpetual whirlpool flow. This can explain an ever constant battle with certain algae.

GOOD STUFF! :D
 
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