180¦ bend L/D

[TeeAr]

Hi there, hope somebody can help me

I have a 180 bend and I'd like to find the value that allows me to find the equivalent length, that is
(L/D)eq = ?

I am looking for values for pipes having various radius.

when looking in previous posts, I found
thread378-8478.
Nonetheless, I'd like to find the L/D value, since I'd like to obtain an equivalent length.

Many thanks

 

[StoneCold]

TeeAr
Crane 410 gives a value of K=50*ft for a Close Radius bend of 180 degrees. Where ft is the friction factor in turbulent flow.

Hope that helps.

Regards
StoneCold

 

[katmar]

The resistance of the bend depends quite strongly on the ratio of the bend radius to the pipe diameter - the r/d ratio. A table for this is in the Crane 410 manual on page A-29.

Crane gives formulas for calculating the K values for a variety of fittings for fully developed turbulent flow. Most of the formuals are in the form of the equation given above by StoneCold, i.e. in terms of [ƒ][sub]T[/sub] which is the Moody friction factor under fully developed turbulent flow.

Since K=[ƒ][sub]T[/sub](L/D) once you know [ƒ][sub]T[/sub] you can calculate the L/D ratio you require by dividing the calculated K value by [ƒ][sub]T[/sub]. By comparing this formula with that given by StoneCold you can immediately see that the constant in the Crane formula is in fact the (L/D) ratio. An inportant factor to remember is that the Crane K values (and indeed most of the K values you will find tabulated in the literature) are for fully developed turbulent flow.

Once you have divided the K value by [ƒ][sub]T[/sub] (which is for turbulent flow) and you have extracted the (L/D) for the bend you can use this equivalent length for laminar flow as well with much better accuracy than if you tried to apply a Crane K value to laminar flow. Using euivalent lengths you should still expect errors of up to a factor of 2 - i.e. you will calculate answers that are between 50% and 200% of the "correct" answer.

Katmar Software - Engineering & Risk Analysis Software

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[metalonis]

The equivalent straight length of a pipe or tube 180° bend is (1/2)•?•D, or ?•r, where r=bend radius.

 

[racookpe1978]

"The equivalent straight length of a pipe or tube 180° bend is (1/2)•?•D, or ?•r, where r=bend radius."

Sure - That's the physical length of the centerline of a perfect arc.

But that won't give you the weight (centerline length*weight/ft for a nominal pipe won't be exactly correct, you need to check the supplier's catalogs for actual weight for each vender); and the required length for fabricating the bend is not that length - since they require extra lengths to draw the pipe through the bending machine; and the equivalent hydraulic length needs to come from the Crane catalog charts - or something equal.

 

[vpl]

TeeAr

Let me add to the voices suggesting that you obtain a copy of Crane Technical Paper 410 "Flow of Fluids through Valves, Fittings, and Pipe."

If you ask around your office, you will probably find someone who has a copy. However, it is a relatively inexpensive book to buy and will probably prove useful to have. Here's a link to the Flow of Fluids website:

http://www.flowoffluids.com/

Patricia Lougheed

******

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