# Do Fluval Ribbed Hoses Reduce Flow?



## Julian (22 Nov 2014)

Or should I stick to the cheap clear PVC stuff?


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## candymancan (3 Dec 2014)

Ribbed anything reduces flow...  Ribbed air intake boxes for cars reduce air flow.. smooth ones are better.. and water flows a lot like air.. so I would stick with smooth surfaces


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## Julian (3 Dec 2014)

candymancan said:


> Ribbed anything reduces flow...  Ribbed air intake boxes for cars reduce air flow.. smooth ones are better.. and water flows a lot like air.. so I would stick with smooth surfaces



I thought that may be the case, thanks for the input.

Any idea on a ballpark % for how much difference it makes? I will get around to testing it one day...


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## ajm83 (3 Dec 2014)

Why do they spec them then? It can't be for flexibility since the instructions for Fluval filters specifically mention using straight runs for the pipes.


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## ian_m (3 Dec 2014)

candymancan said:


> smooth ones are better..


Nope. The ribbed surface actually produces a better flow size for size than a smooth walled tube due to producing laminar fluid flow. Search Google images to see pictures of laminar flow. This is also the reason golf balls have pimples, tennis balls are hairy, cricket balls have stitching, they induce laminar flow across the surface and have much less air resistance than an equivalent smooth surfaced ball.

Other points are (good and bad are)
- Ribbed tubes are generally more flexible than smooth walled tubes.
- Ribbed tubes are stronger than equivalent smooth walled tubes, often having reinforcing in the ribs.
- Ribbed tubes use less material.
- Ribbed tubes can collect detritus in the ribs disrupting the laminar flow, however carefully designed ribbed tubed encourage flow in the ribs to keep detritus out.
- Ribbed tubes can be a pain to join/connect via compression fittings, often special connectors are needed.


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## ceg4048 (3 Dec 2014)

Actually  it's just the opposite. Laminar flow is disrupted by dimples, stitching and hair.
The undesirable drag induced by laminar flow is due to flow separation from the surface. Flow separation from the objects surface increases the local static pressure against which the object must flow. Turbulent flow has a higher energy and adheres to the surface, reduces separation, but has higher skin friction drag.

Cheers,


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## candymancan (4 Dec 2014)

If ribbed tubing was best for air flow... performance engines and performance intakes would all be ribbed... instead they are smooth and stock intakes or regular engines are usually always ribbed.

read this, corrugated tubing reduces laminar flow.......  You are talking about turbulent flow with corrugated tubing

http://www.thelotusforums.com/forum...d-its-adverse-effects-on-the-intake-air-flow/


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## ian_m (4 Dec 2014)

The link you sent talks about air, completely different for liquids.

Actually, looking back on my old hydraulic book, we are both wrong and both right. It depends on the Reynolds number (property of fluid and flow) and Mannings number (property of pipe). Under the right conditions of fluid type and flow you can get better flow in ribbed tubing ie less energy loss per unit length, but depends on rib sizes and flow rate. As we don't know rib size and flow maybe smooth is a better choice.


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## ceg4048 (4 Dec 2014)

ian_m said:


> The link you sent talks about air, completely different for liquids.


For Newtonian fluids the equations of motion  are the same, whether gaseous or liquid. Water and air are both Newtonian. What differs is the value of the parameters, such as density and viscosity, which are much higher in liquids. Of course, gasses are much more compressible than are liquids, but compressibility is accounted for in the viscosity calculation.

The Reynolds number is just the ratio (i.e simple division) of inertial forces to the viscous forces which are present in a flow field. The inertial forces would be the thrust or other pumping force causing the fluid to move or causing the object to move within the fluid, while the viscous forces would be the frictional property of the fluid and objects within the flow field.

When the inertial forces are low then the Reynolds number is also low and the result is a laminar flow field. When the inertial forces are high then the Reynolds number will tend to be higher and this causes turbulence.

In our application we are dealing with lower Reynolds numbers and typically laminar flow, but laminar flows are weak because the inertial forces are low, and so they are easily disrupted. Any increase in turbulence  in a low Reynolds number environment tends to immediately increases the drag and tends to lower the output mass flow rate.

The Manning coefficient is another frictional coefficient used in the denominator of the channel flow equations, so high Manning numbers reduce mass flow rate, while low Manning numbers increase the mass flow rate. Internally corrugated tubing will always have a higher Manning number.

So there are very few conditions that we will face where internally corrugated tubing would result in higher flow rates. The data illustrated in the link above is valid for our case.

Cheers,


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## Jose (4 Dec 2014)

Its quite intuitive isnt it? The more objects/shapes in the way of the flow the slower its going to travel. I understand what you are all talking about since chemical engineering is my field but it can still be seen in the simplest of ways.


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## ceg4048 (4 Dec 2014)

Well, as Ian quite rightly pointed out, a dimpled golf ball will travel faster and farther than a smooth one, so in some regimes of fluid flow the less intuitive things do occur...

Many bizarre things happen with fluids are in motion. The boundary layer issue is one of those things which is why we need a higher flow rate across the leaf, however, there is only a narrow band of higher velocity that produces positive effects. Flow rates above and below that band reduces photosynthetic rates. In fact, since the boundary layer is thinnest at the leading edge of the leaf and grows thicker along the leaf span, photosynthetic rates on the leaf are highest at the edge of the leaf which first contacts the flow., not at the middle or trailing edge of the leaf. This is one of the reasons why two plants can be sitting right next to each other in a tank and one plant does well while the other suffers deficiencies. The orientation of the leaf with respect to the flow field can make a huge difference.

Cheers,


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## Jose (4 Dec 2014)

Actually the roughness in sports balls is to have more control over it. In the case of a golf ball, if you were to hit a smooth one god knows where it would go and there would be more slipage between the ball and the club. This rugosity in the ball doesnt make it travel faster per se, but the golfer is able to hit it in a more controlled way, and harder in the end. The same happens in any sports, smooth is not good because you have less control over where the ball goes, whether it be baseball, cricket, football or any other.

More rugosity or uneven surfaces always means more friction with the fluid in question and less speed.


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## ceg4048 (5 Dec 2014)

No, that is not correct. 
Again, you are depending on intuition and that has little basis on science. The turbulent flow causes by the rotating dimples on the surface of the ball increases the energy of the flow around the sphere. As I mentioned, boundary layer separation on a sphere increases the drag due to the increased static pressure in front of the sphere that occurs when the boundary layer detaches from the sphere. Detachment occurs more readily when the flow is laminar. Increasing the turbulence allows the boundary layer to adhere to the sphere, reducing the static pressure in front of the sphere. The sphere can then move more easily against a lower static pressure.

The player can more easily manipulate the trajectory of the ball by spinning it around each axis. If the ball spun around a vertical axis then the static pressure will be reduced on the left or right side of the ball and the ball will move to the left or right. If the ball is spun around the lateral axis then the static pressure will be reduced above or below the ball and it's trajectory will be perturbed either upward or downward.

Clever players of whatever sport will understand the idea of spinning the ball around these axes in order to move the ball on the desired trajectory, but this is strictly an aerodynamic principle. Whatever other attributes occur as a result of the ribbing, hair or dimples is secondary.

Cheers,


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## Jose (5 Dec 2014)

ceg4048 said:


> No, that is not correct.
> Again, you are depending on intuition and that has little basis on science. The turbulent flow causes by the rotating dimples on the surface of the ball increases the energy of the flow around the sphere. As I mentioned, boundary layer separation on a sphere increases the drag due to the increased static pressure in front of the sphere that occurs when the boundary layer detaches from the sphere. Detachment occurs more readily when the flow is laminar. Increasing the turbulence allows the boundary layer to adhere to the sphere, reducing the static pressure in front of the sphere. The sphere can then move more easily against a lower static pressure.
> The player can more easily manipulate the trajectory of the ball by spinning it around each axis. If the ball spun around a vertical axis then the static pressure will be reduced on the left or right side of the ball and the ball will move to the left or right. If the ball is spun around the lateral axis then the static pressure will be reduced above or below the ball and it's trajectory will be perturbed either upward or downward.
> Clever players of whatever sport will understand the idea of spinning the ball around these axes in order to move the ball on the desired trajectory, but this is strictly an aerodynamic principle. Whatever other attributes occur as a result of the ribbing, hair or dimples is secondary.



Yes I have to admit you are right. But this is a case not comparable to our aquariums because:
1: Its very high speeds which we are not likely to accomplish in water in real life.
2. Its an object travelling through a fluid not a fluid travelling through a pipe.
3. This phenomenom is really a few things happening at the same time and not only the force of friction with the surface which is really what I was referring to.

For water we can extrapolate that more accidents/shapes in the pipe mean less speed.


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## ceg4048 (5 Dec 2014)

1. Speed alone is not the only relevant parameter in the equations of fluid motion. Density, Pressure, Geometry and aerodynamic properties are just as relevant, if not more so.

2. The kinematics and dynamics of fluid motion does not care if the object is moving against a stationary fluid or if a fluid is in motion against a stationary object. The forces that develop as a result of the relative motion are exactly identical if all other parameters used in the equation are equal.

3. The friction developed are a direct result of forces caused by the relative motion. That is what Ian mentions as the Reynolds number. If you want to compare the forces that develop in  relative motion of different fluids against  objects then the Reynolds number of the two phenomenons must be compared. Therefore, if the Reynolds number of the fluid in your pipe or aquarium is similar to the Reynolds number of your tennis ball then the forces that develop are directly comparable. That also is not intuitive but is true. Again, I refer you to the graph shown in the Opening Post in the link above which plots frictional coefficient versus Reynolds number. The chart is not ONLY for automobiles. It has many applications. The chart also defines for you the laminar flow regions, the transition zone as well as the turbulent zone.

There is no need to extrapolate anything. The laws of fluid motion are the same for the aquarium pipes as they are for a river channel or an automobile exhaust. In these cases, where the Reynolds numbers are similarly low, the flow is laminar, and introduction of turbulence on a laminar flow condition increases drag, which reduces flow rate.

Cheers,


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## Jose (5 Dec 2014)

Yeah I suppose they are all the same but. Have you got an example like the golf ball for a fluid?


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## Jose (5 Dec 2014)

ceg4048 said:


> 2. The kinematics and dynamics of fluid motion does not care if the object is moving against a stationary fluid or if a fluid is in motion against a stationary object. The forces that develop as a result of the relative motion are exactly identical if all other parameters used in the equation are equal.



By the way, the equations are the same but normally to represent the behaviour of a fluid/object in a fluid you need a program (like for the case of a golfball) which integrates much more info. A program with those equations in but used in a more complex way. For example: In the case of the golf ball those dragging forces act on the ball modifying its behaviour whilst in a liquid those forces would act on the fluid which wouldnt have the same response. And the forces would also act over the tube which isnt moving so the result isnt the same.


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## Jose (5 Dec 2014)

ceg4048 said:


> There is no need to extrapolate anything. The laws of fluid motion are the same for the aquarium pipes as they are for a river channel or an automobile exhaust. In these cases, where the Reynolds numbers are similarly low, the flow is laminar, and introduction of turbulence on a laminar flow condition increases drag, which reduces flow rate.



This is the scenario in our pipes so this is what we should be telling people without the understanding of this field. Because most people arent going to use the equations.



ceg4048 said:


> 1. Speed alone is not the only relevant parameter in the equations of fluid motion. Density, Pressure, Geometry and aerodynamic properties are just as relevant, if not more so.


Its not the only factor but its the one we are interested in the most. We want to maximize it.


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## naughtymoose (5 Dec 2014)

So, the science of fluid dynamics lost me a bit, and the bit about golf balls almost put me to sleep (I don't like golf!) I would have perked up a bit if mention had been made of Cricket balls or Rugby balls...

I have the same dilemma as the OP, Julian.

When I put the second Fluval 306 on MY tank, to be delivered just before Christmas, should I use ribbed Fluval hose or plain smooth hose?

Will it come down to cost? Or is there a genuine improvement to be gained by using ribbed hoses? If so, why don't all filters use ribbed hose?


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## Jose (5 Dec 2014)

naughtymoose said:


> So, the science of fluid dynamics lost me a bit, and the bit about golf balls almost put me to sleep (I don't like golf!) I would have perked up a bit if mention had been made of Cricket balls or Rugby balls...
> I have the same dilemma as the OP, Julian.
> When I put the second Fluval 306 on MY tank, to be delivered just before Christmas, should I use ribbed Fluval hose or plain smooth hose?
> Will it come down to cost? Or is there a genuine improvement to be gained by using ribbed hoses? If so, why don't all filters use ribbed hose?



See what I mean ceg? Thats why I made the generalization I di before. Ribbed hoses are always going to mean less flow for us. We are talking about comparing same diameter hoses of course.


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## ceg4048 (6 Dec 2014)

Again, your generalizations are missing the point. In order to gain insight into the phenomenon you have to investigate the reasons. We are NOT interested in speed. How many times is it necessary to state that? The goal of flow/distribution is mass flow rate, not speed. You can achieve satisfactory results by using low speed but by moving a high mass of water. SOMETIMES more speed is required and SOMETIMES more mass is needed. That's how the equations work. I don't care if people are not interested in the equations, but they better understand the principles involved, otherwise they will aim for the wrong target.

Cheers,


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## naughtymoose (6 Dec 2014)

OK. Clive, I've read tons of posts on this site, and I am truly grateful for the knowledge that you pass on to us.

The question remains.

Should we use ribbed or no-ribbed hoses? If one, why not the other? Simple explanations really help sometimes!

Why do YOU think that Fluval makes ribbed hoses? I think that it could possibly have a marketing connection.


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## Jose (6 Dec 2014)

Ok ceg. But volumetric flow/hose area=speed. Volumetric flow is proportional to mass flow here. If we have a certain hose its section area isnt going to change, so in our hose its basically interchangeble to speak of flow or speed. When we have to distinguish between the two is when our area changes like when we drill holes into the hose. Anyway, do you know of a case where something that isnt intuitive like the golf ball phenomenon happens in a hose? I just wonder cause as you may have noticed I am quite ignorant and dont want to generilize if its wrong.
maybe a dimbled hose would be ideal?


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## ceg4048 (7 Dec 2014)

naughtymoose said:


> The question remains.


As mentioned, assuming the similar diameters, a smooth walled tube generally will produce better flow rate. Again, it has not really been verified that the ribbed tubing in question actually has a corrugated inner wall.  This whole discussion can be moot if the ribbing is only on the external wall.  Stick your finger in the tube and find out if the inner walls are ribbed or not. If not then forget everything in this thread and just carry on using the tube. If there is internal ribbing then a smooth bore tubing will likely be a better option.




naughtymoose said:


> Why do YOU think that Fluval makes ribbed hoses?


I assume that the ribbed tubing is less susceptible to kinking, and kinking is a recurring problem. However, they also sometimes use larger diameter tubes, and the pump performance within the filters are a factor as well. So if you compare the throughput of their FX5 (25mm tubing) with Eheim's 2080 you'll find that the throughput of the FX5 is higher, again, for various reasons in the system design. 

Cheers,


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## naughtymoose (7 Dec 2014)

Clive,

I just checked the interior of the Fluval hose. It is ribbed, the plastic itself is quite thin too. I agree totally with the kinking issue. We moved a washing machine yesterday and the rubber water hose kinked. I used to use corrugated/ribbed pipes on electrical installations, and the reasons are the same.

So i'll be getting smooth bore pipe when I fit both the Fluval 306 filters rather than buy longer Fluval pipes.

Many thanks.

Colin


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