Thread: Ducting Branches

100 = 7.8sq cm
150 = 17 sq cm

17-(7.8+7.8)=1.4.

Less the flow from the flexible lines to the machine, that's not good as it will be a fair way behind, back to the drawing board as I was under the impression it was a lot closer than that. I was going to use a version of the two into one transiition here...

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Thinking out loud, if clearvue are selling them then maybe it does not make a huge difference. My bandsaw, thicknesser and jointer have a single 100mm port so I was going to add a second one to the BS and jointer and enlarge the one on the thicknesser to keep up the flow. I can see this job being a bit long winded.

Hmm. The difference is 1.4sq cm, that's equal to approx 12mm diameter. In other words, you're missing out of the flow you could get through a piece of garden hose. I really can't see how it would be a problem...near enough for me.

2 at 100 is close enough to 1 by 150.
losses increase on bends
flexible pipe is even worse

Extra horsepower always helps.

Thanks guys, maths and me are enemies. I had a feeling it would not be much. The only issue is double the flex hose and I suspect they would slow down a lot more than one 150mm due to turbulance. BTW have you seen this video on turbulance......

YouTube - Turbulence

Enjoy, OS viewers might not get it.

Basically u r comparing one area with another
A1=A2
which becomes
D=(nd2)1/2.............it doesn't write maths equatios too well
D is the diameter of the unknown (in this case we think it might be 150)
n is the number of smaller pipe size ( 2)
d is the diameter of the small pipe (100)
2 is d squared (multiplied by itself) (100x100)
1/2 is square root of everything in the brackets
therefore
D=(2x100x100) 1/2
= 141mm
so 2 100mm pipes equals 141mm pipe
150mm pipe just means that airflow speed will be a little slower than the airspeed in the 100mm pipes which doesn't matter, it might even give u a little more flow as u now have a slightly reduced friction loss in the 150 pipe....but, if it's too slow the chips will fall out of the airstream and lay in the bottom of your 150mm pipe, not good, from Bill Pentz's web site in horizontal runs he recomends 2800f/m (as a minimum) which works out to be ~530cfm in a 150 pipe.

Most 1hp units claim figures of 600 to 900 ish (this is mostly with nothing hooked up to the unit) a 2hp in the area of 1500cfm so this is probably the minimum size unit to have hooked upto a 150mm pipe


Pete

Originally Posted by Mini

Thanks guys, maths and me are enemies. I had a feeling it would not be much. The only issue is double the flex hose and I suspect they would slow down a lot more than one 150mm due to turbulance. BTW have you seen this video on turbulance......

YouTube - Turbulence

Enjoy, OS viewers might not get it.

Mini is correct the smaller the pipe the more the turbulent flow, especially on junctions.
Even in straight line runs a 100 mm acts more like a 90 in practice, and a 150 acts like a 140 so now its 15.4 sq cm V 6.4 so the difference instead of being 1.7 is actually 2.8 sq cm. At junctions it could be double that again

I have made the first of the 150 to 2x100 adaptors to see how it turned out. I would prefer to buy Clearvue's version but it is much cheaper to make my own, unfortunately for Ed as I think his stuff is well done and reasonable in price to go with it. The killer is the freight when it costs me nothing to make my own as I have a heap of 5mm perspex to get rid of. the Clearvue item is here....

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My understanding of turb. in a (straight smooth walled) pipe is more a function of the velocity (and pressure,density,viscosity) (Reynolds number equates all these factors) of the flowing (air) smooth laminar flow occours upto a given speed, after that turbulence increases and limits any gains in flow that u might be trying to achieve.

If we look further into the flow in a pipe we also see that the laminar flow is not evenly distibuted across the diameter of the pipe,
Attachment 133712
The red line indicating air speed....lowest at the pipe wall, highest at the centre.
BobL, Is this what u r pointing to re small v large pipes?, feel free to correct me

Attachment 133713
This is laminar flow but a small obstruction promotes local turbulence.
Sharp corners, things poking into the pipe, edges, corrugations all promote turbulence as well and should be kept to the absolute minimum.

There is a heap of utube vids showing laminar/turb flow....quite interesting, some might say if u r a geek but I say armed with a little knowledge (can be a dangerous thing) allows u to understand a little better the physics of what is going on, maybe


Pete

Originally Posted by Mini

I have made the first of the 150 to 2x100 adaptors to see how it turned out. I would prefer to buy Clearvue's version but it is much cheaper to make my own, unfortunately for Ed as I think his stuff is well done and reasonable in price to go with it. The killer is the freight when it costs me nothing to make my own as I have a heap of 5mm perspex to get rid of. the Clearvue item is here....

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Yep this is a much easier thing to make than a transition like this
Attachment 133714

If u can try to make it so u have the minimum sharp corners, even if u do things like fill up the corners with splonk/bog or whatever sticks to perspex. every little bit helps

Pete

My comment on turbulence was that two flex hoses of 100mm would slow the air flow a lot more than one flex line of 150mm even though mathematically they would flow very close to each other. Of course turbulence is a product of air flow speed but it could be useful as well. A very turbulent flow will suspend more material than a smooth laminer flow, or it seems to me it would in my naive view of fluids and how they work.

Originally Posted by pjt

My understanding of turb. in a (straight smooth walled) pipe is more a function of the velocity (and pressure,density,viscosity) (Reynolds number equates all these factors) of the flowing (air) smooth laminar flow occours upto a given speed, after that turbulence increases and limits any gains in flow that u might be trying to achieve.

If we look further into the flow in a pipe we also see that the laminar flow is not evenly distibuted across the diameter of the pipe,
Attachment 133712
The red line indicating air speed....lowest at the pipe wall, highest at the centre.
BobL, Is this what u r pointing to re small v large pipes?, feel free to correct me

The 100 becoming effectively 90, and 150 becoming effectively 140 is a boundary layer issue - boundary layer effects are effectively the same as turbulent flow at the boundary. A 10 mm effective boundary layer for a no join smooth pipe is an over estimate but as soon as you put joints, junctions and blast gates in the lines, its probably about right. I did some measurements of air flow differences at work about 25 years ago and found a 20% difference between 2 x 100 mm and 1 x 150 mm pipe, but it varies a lot with airspeed, and joint and junction design. Certainly the flow in the 100 hit total turbulence at lower air speeds than the 150.

Originally Posted by BobL

Certainly the flow in the 100 hit total turbulence at lower air speeds than the 150.

I would have bet that was the case as in all the other stuff I have played this was so, a smaller diameter equals greater turbulence at a lower speed. I wonder at what air speed turbulence becomes effective in a given duct size, because that would be what happens. Its occurrence would coincide with the ability of the air stream to hold the material in suspension in any given diameter duct. I'm getting a headache thinking about all this stuff, I haven't touched it in a long time.

One more thing, from memory all DCs operate in the turbulent zone of air speeds anyway