Pressure drop diff between 90 deg Elbow and Bent pipe 1

[StoneCold]

Where can you find values to determine the pressure drop difference between a 90 Degree butt-weld elbow fitting and bending the pipe into a 90 degree elbow? Lets say the pipe is 6" Sch 40 Carbon Steel(not that it matters). The fitting is a 1.5xradius elbow and we would bend the pipe on a 6xradius bend. My crane book gives K values for the elbow but not for a bent pipe? Would there be any difference than saying the bent pipe was equivalent to a 6xradius elbow?

Regards
StoneCol.

 

[LHA]

I would imagine the losses through a bent pipe would be much higher than through a manufactured fitting. Everytime I've ever bent a pipe - metal or plastic - there has been some deformation which would lead to an imperfect inside diameter. That is a flow obstruction.

Don't know of any data pertaining to such though.

Engineering is the practice of the art of science - Steve

 

[STYMIEDPIPER]

Review Crane "Flow of Fluids" 90 degree bends

For r/d = 6 then K = 17 fT
For r/d = 8 then K = 24 fT
For r/d = 10 then K= 30 fT

For 6 in std pipe fT = 0.015

r/d = 36/6 =6
6 = 17 fT
hence
Resistance Coefficient 90 deg bend
K = 17 x 0.015 = 0.255

Crane also defines formula for bends other than 90 deg

 

[katmar]

It would depend so much on the quality of the workmanship that it is impossible to give a definitive answer. If the bend was done properly I would expect the resistance to be very similar to a fabricated bend of the same radius. On the other hand, if it became severely corrugated on the inside of the bend it could be significantly more.

It also depends on how accurate you want to be. To put it in some sort of perspective, these are some K-values for water flowing at 2.5 m/s in a 100 mm pipe

6d fabricated bend : K = 0.29
90 degree mitre bend, single weld : K = 1.0
90 degree mitre bend, two welds : K = 0.50
90 degree mitre bend, three welds : K = 0.40

If your fabricated bend is not a large part of the overall resistance you do not need to be too accurate.

A useful comparison of the effect of bend radius on resistance has been done by Dennis Kirk, who often posts here and hopefully will have some advice for you. See Dennis' graph at

http://members.ozemail.com.au/~denniskb/work/bendel.gif

Harvey

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[katmar]

I just came across this reference which claims that the K-value for a bend with a corrugated inner radius is 1.3 to 1.6 times the value for a smooth bend.

See

http://www.westerndynamics.com/Download/friclossfittings.pdf

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[tom73]

For free flow rate calculation go to

http://www.1728.com/flowrate.htm

 

[vzeos]

The attached link has a pretty good equivalent length calculator. You can assign the bend angle and the r/d value.

http://kirkmansoftware.com/