How does it work? Vol 3: Closed loop

[Matt L.]

Still no Magic, but...

jango is correct, the distribution of the water flow out of a "pipe" or other opening is mainly governed by laminar flow.

I believe I understand what you are getting at, but laminar is not the correct term. Laminar flow applies only for certain low Reynold's numbers (Re < 2300), which even if our discharges were perfectly uniform, straight pipes, would not apply. For reefing applications, one may assume that all flow in a pipe is turbulent flow (you're not even likely to get transitional flow).

You may see for yourself with this fun Reynold's number calculator.

For example, with my 3/4-in. discharge carrying 300gph on my closed loop, I get a Reynold's number about 10-times greater than that needed for laminar flow. I would need a flow of 30gph, not 300gph to get laminar flow. And that is if the pipe were pefectly straught and smooth, which it is not.

Moreover, even if the flow were laminar exiting the pipe, it would become turbulent due to shear stress the minute it entered the relatively calm tank waters.

So I disagree that the benefits of the Tunze are due to laminar verus turbulent flow, as any powerhead or closed loop generates turnbulent flow.

But there is still the question as to why the Tunze is so well-liked, and what can we do with our closed loops to mimic the Tunze performance, and for that, I do not have an answer.

Matt

 

[jango]

Matt check out this thread and watch the video's. Just watch how the flow pattern's disperse throughout the tank. The tunze would have an even wider flow pattern.

 

[Matt L.]

Matt check out this thread and watch the video's. Just watch how the flow pattern's disperse throughout the tank. The tunze would have an even wider flow pattern.

Yeah. I watched the videos. The eductor does seem to make some of a difference, although I'm not sure I want to go for one yet.

Matt

 

[Chuck Spyropulos]

I believe I understand what you are getting at, but laminar is not the correct term. Laminar flow applies only for certain low Reynold's numbers (Re < 2300), which even if our discharges were perfectly uniform, straight pipes, would not apply. For reefing applications, one may assume that all flow in a pipe is turbulent flow (you're not even likely to get transitional flow).

You may see for yourself with this fun Reynold's number calculator.

For example, with my 3/4-in. discharge carrying 300gph on my closed loop, I get a Reynold's number about 10-times greater than that needed for laminar flow. I would need a flow of 30gph, not 300gph to get laminar flow. And that is if the pipe were pefectly straught and smooth, which it is not.

Moreover, even if the flow were laminar exiting the pipe, it would become turbulent due to shear stress the minute it entered the relatively calm tank waters.

So I disagree that the benefits of the Tunze are due to laminar verus turbulent flow, as any powerhead or closed loop generates turnbulent flow.

But there is still the question as to why the Tunze is so well-liked, and what can we do with our closed loops to mimic the Tunze performance, and for that, I do not have an answer.

Matt

Yes I was idealizing and calling the pipe straight and the flow at t= 0, the second before the water exits the pipe it can be considered laminar flow in comparison to a propeller. So if one source (pipe) is generating "ideally" laminar flow and the other (propeller) is not, different resulting flow patterns will exist since the resistance of the clam water is the same in each case and can be removed from the equation.

Yes when the water exits the pipe there is turbulence but not totally turbulence...the inside of the water flow path would have some laminar flow left...if this were not the case than the water would flow in a more broad pattern as in the case for the Tunze.

Tunze produce wider flow paths with lower velocity, which is why they are so well liked...also less power, higher flowrate (volume per second or hour etc...), better and finer controlling capability,etc.

 

[Greg Hiller]

A lot of good info above. A few comments.

>Now I have 4 Tunze Turbelle Streams, each of which provides 3000 GPH for a total of 12000 GPH. Each Stream pump uses approximately 45 watts x 4 = 180 watts a decrease in power usage of almost 75% and a factor of 4 increase in water motion. <

I in general agree with what Chuck is saying, but you need to be careful about the calculations, particularly when you start talking about heat generation. Keep in mind if you are using a fully submersible powerhead to generate flow then ANY and ALL watts that are being consumed by the powerhead are eventually converted into heat in the tank. If you are using a closed loop to generate flow then the watts being consumed are not necessarily all getting dumped into the water since some of the heat from the motor is air cooled (of course if the pump's under your stand the heat still enters the room, and potentially the tank). Still, if a closed loop consumes a lot more power for the same water motion (I realize in Chucks example the Tunze creates more flow), then you still might end up better off in terms of excess heat being added to the tank with a Tunze. Think about all the friction losses in the closed loop.

>Is there something that you could attatch to the ends of the closed loop outputs that has a propeller like the Tunze's that would widen the flow?<

Jango answered this, and I'd just like to reiterate. Eductors will spread out the flow at the risk of more frictional losses. I have one of these eductors (never used it yet) and you all should be aware that the tend to be rather large (>6 inches I believe, might be hard to hid in a small tank), and surprisingly expensive for just a hunk of plastic. You could probably build yourself, FWIW.

FWIW, in my 400 gallon system I plan to use a pair of the largest Tunze's available (mostly for the reasons Chuck mentioned) in the ends of the tank, and a pair of return pumps (GRI 520's) returning water from the sump each linked to a 3 way ball valve. In this way the pumps will have a total of four outlets any two of which will be active at one time. The outlets used will vary randomly. I'm using two pumps just for redundency in case of failure.

 

[Chuck Spyropulos]

Hey Greg...you gotta get the new magnetic holders.....really makes it easier to install Streams ! Although they are expensive.

 

[Chuck Spyropulos]

Greg, one more thing...the motors on these pumps are DC and thus give off only a really small amount of heat as compared to AC motors

 

[Chuck Spyropulos]

The Transformers, of course, are not in the water but instead should be kept dry. They DO heat up a little but way way less than a conventional closed loop pump.

 

[jango]

If you have a pressure rated pump you could use penductor's they are pretty small compared to eductors. I wonder if you drilled the whole a little larger on a penductor if it would work better on a lower pressure pump.

 

[Chuck Spyropulos]

"ANY and ALL watts that are being consumed by the powerhead are eventually converted into heat in the tank. If you are using a closed loop to generate flow then the watts being consumed are not necessarily all getting dumped into the water since some of the heat from the motor is air cooled (of course if the pump's under your stand the heat still enters the room, and potentially the tank"

I disagree...Some of the power goes into driving the propeller and some is converted into heat depending on the efficiency of the device...Did you mean " Any and All watts that are not consumed....."?

 

[Greg Hiller]

Chuck,

Since I don't have the Tunze's yet, I didn't know/didn't think about the fact that the transformers are outside of the water. Obviously, whatever heat they are giving out does not enter the water. HOWEVER, any and all electricity that flows into the powerhead itself is converted into heat. There's this little thing somebody came up with called the conservation of energy. Any kinetic energy that you add to the water is converted into frictional energy, and heats the water. No getting around this one I'm afraid unless you can mount part of the unit out of the water like the old Gemini powerheads that Larry Jackson used to like so much.

>Hey Greg...you gotta get the new magnetic holders.....really makes it easier to install Streams <

I had not planned on purchasing them. I was under the impression that the Streams came with brackets that were designed for Euro-braced tanks, of which mine is one. The cost of the Streams themselves was enough to set me back for quite some time!

 

[Matt L.]

Yes when the water exits the pipe there is turbulence but not totally turbulence...the inside of the water flow path would have some laminar flow left...if this were not the case than the water would flow in a more broad pattern as in the case for the Tunze.

Chuck,

I think once again I am arguing semantics... Do you remember how I flipped out when the term "closed loop" arose, which is hydraulically incorrect, but has nonetheless found common usage among the reef community?

Anyway, for the viewers at home, I must respectfully make the correction that at no point is the flow exiting a closed loop ever laminar (unless you were using too little flow to be effective, see above).

It is also not really correct to say something is more laminar than another when they are both turbulent. You can say something is more turbulent than another, and you could say that one flow stream has a lower Reynolds number than another. And I think that is what you are getting at.

I do not disagree with you that the flow pattern out of a Tunze stream is different and better than that of a standard orifice discharge.

Tunze produce wider flow paths with lower velocity, which is why they are so well liked...also less power, higher flowrate (volume per second or hour etc...), better and finer controlling capability,etc.

Even before Greg said it, I was considering the addition of a Tunze Stream to the side of my aquarium. Like Greg, I have a closed loop on the back, and for aesthetics, I cannot add a closed loop around the side. I was hoping I could get away with just the closed loop, but no such luck. The downside is that the Tunzes are just so expensive,

Matt

 

[Brimc]

What are you using to prevent your tank from draining into your sump in the case of a power failure??

 

[JohnK]

FWIW the Tunze 6060 (1600 GPH, not adjustable, doesn't use a seperate controller, will add a tiny bit more heat) is only about $130, pretty reasonable compared to an average "closed loop" set up.

Wasn't this a thread about closed loops?

 

[nunofs]

Brimc: who is your question directed to? In any case, as we're discussing closed-loops, the issue of draining into the sump doesn't exist because the closed-loop, as the name implies, is self-contained... in the case of power failure, the water will just stay in the pipes because it's all at the same surface level (the level of the main tank).

Nuno

 

[JayG]

According to Roger of Tunze USA the Tunze stream 6000 will add less than 1 degree in 150G tank.

 

[Chuck Spyropulos]

No Way

Chuck,

Since I don't have the Tunze's yet, I didn't know/didn't think about the fact that the transformers are outside of the water. Obviously, whatever heat they are giving out does not enter the water. HOWEVER, any and all electricity that flows into the powerhead itself is converted into heat. There's this little thing somebody came up with called the conservation of energy. Any kinetic energy that you add to the water is converted into frictional energy, and heats the water. No getting around this one I'm afraid unless you can mount part of the unit out of the water like the old Gemini powerheads that Larry Jackson used to like so much.

>Hey Greg...you gotta get the new magnetic holders.....really makes it easier to install Streams <

I had not planned on purchasing them. I was under the impression that the Streams came with brackets that were designed for Euro-braced tanks, of which mine is one. The cost of the Streams themselves was enough to set me back for quite some time!

What???? What you are saying is impossible! Most of the energy going into the Tunze is given up to the water as kinetic energy...i.e. the Tunze converts electrical energy into kinetic energy(water motion) and some minute, and neglible amount of heat. Hence it does not violate the conservation of energy principle. If all of the electrical energy goes into heating up the water, then there would be no energy left to move the water...and THAT WOULD violate the conservation of energy principle.

 

[Brimc]

Thanks Nunofs I did not follow the diagram close enough, now I understand

 

[Chuck Spyropulos]

Greg, I think the heat you are referring to is the heat that is dissipated in the process that brings the water back to calm, or that converts the kinetic energy of the moving water into heat. Of course this is all due to friction and yes the product of friction is heat. The water hits the side of the tank, scrapes across the tank surfaces, etc and the product is heat. However, the water is also cooling naturally during the evaporation process. This effect, plus the fact that you need much more energy to heat up the water than you do to move it, makes this effect negligible. If this were not the case then we would use pumps or water motion instead of resistive heaters to heat our water when required !

Also this effect occurs regardless of how you input the kinetic energy (powerheads, Streams, external pumps), and as such is not a discriminating factor when comparing the performance of these devices.

 

[Greg Hiller]

Chuck....what happens to the kinetic energy? Does it accumulate? You keep putting it into the tank, does the water flow keep speeding up?

I agree that initially the electric energy is converted into kinetic energy (as I said above), and some waste heat since the motor is not 100% efficient. BUT, and this is a big but, the kinetic energy...all of it...is quickly converted into heat.

An easy way to look at it would be if you turn the pump off the water motion slows down and then stops right? The kinetic energy is converted into heat as the molecules of water 'rub' against each other.

ANY device you put into a container of water and run electricity into is going to convert all that energy into heat, unless it is converting the energy into chemical or... ...nuclear energy. Not likely nuclear, and chemical energy is not likely unless you are making hydrogen and oxygen via electroysis, or separating ions, etc.

Here's another way to look at it....suppose you had a small plastic box that had a paddle wheel inside and a crank that ran out of the box though a seal (a classic experiment in thermodynamics, BTW). If you crank on the paddle from outside the box you are creating water motion inside the box without directly adding external heat to the box. The water in the box will heat up over time as ALL the kinetic energy you put into the water is converted to heat.