How much restriction or flow loss from tight 90 degree bend?

RonA

RonA

Active member
Just curious if anyone has calculated loss of flow from the bends in our turbo plumbing. This cast piece is a sharp 90deg that starts out at 3" id on the flange end and transitions to 2.690" id on the small end. If I cut it off and weld on a piece that it 3" id and blend it, it will still have to go down to about 2 3/4" id at the intercooler. Better to go larger all the way to the intercooler so it becomes the first restriction, or does it matter?



Thanks.
RonA
 

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Keeping smaller diameter pipe between turbo and intercooler is not a bad idea, temperature is high and keeps velocities up.
As air cools off and becomes more dense, then more attention needs to be paid to flow restrictions and speeds.
When i get back to my work computer i can plug numbers into a caculator to figure flow loss.
If you have the room, a large radius (6") aluminum 90* welded directly to the flange would be most ideal, but you should be fine with the elbow as is.
 
Its still a step bigger than the compressor outlet isn't it?

Sent from my DROID RAZR HD using Xparent BlueTapatalk 2
 
Look up Tom Vaught over at theturboforums.com. He was the senior engineer for boosted engine systems at ford for many years, so he'd have had the resources to test this stuff thoroughly...

I know he's recommended against sharp radius bends coming directly out of the compressor in the past... Unfortunately it's something most of us will have to deal with for packaging reasons. But I think anything you can do to smooth flow there point would be beneficial.$.02
 
I know on the exhaust side, one 90* bend is equal to 5ft of straight pipe. I think that on the intake side the 90 wouldn't add that much restriction, but the turbulence created by the air bouncing off of that tight curve would.
 
This help ya???

let’s cut to the chase – what are some of the useful figures? Let’s take a 3-inch tube: that’s pretty common these days on both high performance exhausts and intakes. A tight 90-degree bend (where ‘tight’ means a radius about equal to the diameter, ie in this case 3 inches) poses the same restriction as 7.5 feet (2.3 metres) of straight pipe!

A long radius 90-degree bend (a bend radius of 4.5 inches, or 11.4cm) has a flow restriction equal to about 5 feet (about 1.5 metres) of straight pipe.

A 45-degree bend? Well, one with a radius of bend the same as its 3-inch diameter has an equivalent flow restriction of 4 feet, or about 1.2 metres. A 180-degree bend with a 1:1 radius/diameter? It’s got the same flow restriction as 12 feet of straight pipe – that’s an incredible 3.7 metres!

Get the picture? Those bends – even when they are relatively open – drop flow to a major degree. If the mass of air contained within the pipework isn’t critical (eg as it is for intercooler plumbing, where throttle response loss needs to be minimised) it makes a helluva lot of sense to go much longer rather than put in tight bends.

And we’ve all seen those intercooler plumbing constructions where someone hasn’t bothered using a bend at all – instead they’ve welded a 90-degree mitred join into the plumbing. The Carrier book suggests that in 3-inch tube, such a join has the equivalent flow restriction of nearly 4.6 metres of straight plumbing….

And what about other pipe diameters? Some other data from the book is reproduced here:

Losses in equivalent feet of straight pipe:

SMOOTH BEND ELBOWS
Pipe Size 90-degree standard 90-degree long radius 45-degree standard 180-degree standard
2 inch 5.0 3.3 2.6 8.2
2½ 6.0 4.1 3.2 10
3 7.5 5.0 4.0 12
3½ 9.0 5.9 4.7 15
4 10 6.7 5.2 17
5 13 8.2 6.5 21
‘Standard’ = radius/diameter ratio of 1. ‘Long Radius’ = radius/diameter ratio of 1.5.

MITRED ELBOWS
Pipe Size 90-degree 60-degree 45-degree 30-degree
2 inch 10 4.5 2.3 1.3
2½ 12 5.2 2.8 1.7
3 15 6.4 3.2 2.0
3½ 18 7.3 4.0 2.4
4 21 8.5 4.5 2.7
5 25 11 6.0 3.2
 
I haven't thought about it much, but are the losses linear with flow?

It would seem to me that bends would progressively get more problematic as the flow keeps increasing toward the normally accepted limits for the size(usually limited by velocity, right)?

Or am I looking at it incorrectly?
 
best flowing 90 degree bend is cobras neck type, like some jap motorcycles are using in exhaust manifolds. I have also seen 180 degree bend flow better than 90 degree, I think it was Erland at Speedtalk who showed the flowbench numbers some time ago.
 
Yes the losses become exponentially greater as the velocity increases. Double the air speed, quadruple the loss. When I get back to AZ I'll look up the head loss coefficient in my book.

I'd say your friends finding of a 180* bend flowing more is an error or anomaly. He probably had the probe or port or whatever the hell he was using in a "bubble" or stall portion of the tubing.

Pressure can always be used to propagate more mass through a pipe, but gaseous fluids take lots of energy to compress. You'll also hit a Reynolds # limit where the flow in the pipe becomes so turbulent due to high velocity that pumping energy costs skyrocket. Anywho, stick with the elbow the gains from a bigger bend are negligible.
 
RonA said:
Just curious if anyone has calculated loss of flow from the bends in our turbo plumbing. This cast piece is a sharp 90deg that starts out at 3" id on the flange end and transitions to 2.690" id on the small end. If I cut it off and weld on a piece that it 3" id and blend it, it will still have to go down to about 2 3/4" id at the intercooler. Better to go larger all the way to the intercooler so it becomes the first restriction, or does it matter?



Thanks.
RonA
Click to expand...

Ron, go pick up a Crane 410. It has all sorts of good info like this...
 
Values are conservative when compared to some posted in this thread, but they work, and are close enough for our purposes
 

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also keep in mind that all this does is give an "equivelant length" for the system. It does not determine pressure drop. To determine pressure drop we would need the fluid velocity thru the pipe.
 
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