Pressure loss - miter cut pipe or tube
Pressure loss - miter cut pipe or tube
(OP)
Hi there!
I am at loss, need helpful hints.
I need to calculate pressure loss thru a 30" ID formed tubing miter cut and welded together to form a 45° & a 90° elbows. 90° has two miter cuts. 30" leg length.
Looking at Crane data book I see that for alpha=45° =15fT, and for alpha=90° K=60fT.
OK, fine, what do I need to do with this data.
I can't find fT for 30" pipe or tube.
Do I use "Head Loss" = K * v^2/2g?
When I do, I get "HL" = 33' for flow rate of 34785 cubic-ft per minute & fT of 0.01 (I grabbed 0.01 from thin air). So what am I doing wrong. How can a 45° miter cut 30" tube have 33' hl?
Please can someone helpppp!!!
I am at loss, need helpful hints.
I need to calculate pressure loss thru a 30" ID formed tubing miter cut and welded together to form a 45° & a 90° elbows. 90° has two miter cuts. 30" leg length.
Looking at Crane data book I see that for alpha=45° =15fT, and for alpha=90° K=60fT.
OK, fine, what do I need to do with this data.
I can't find fT for 30" pipe or tube.
Do I use "Head Loss" = K * v^2/2g?
When I do, I get "HL" = 33' for flow rate of 34785 cubic-ft per minute & fT of 0.01 (I grabbed 0.01 from thin air). So what am I doing wrong. How can a 45° miter cut 30" tube have 33' hl?
Please can someone helpppp!!!





RE: Pressure loss - miter cut pipe or tube
This would give you a K value for the 45° miter of 0.011 x 15 = 0.165
My calculation agrees closely with your loss of 33 ft for the 45° miter, but don't forget that these a feet of the pumped fluid which I guess is a gas from the velocity of 118 ft/s.
The Crane value of 60fT for the 90° bend is for a single cut bend. You want to take twice the 45° K value for your bend because it is made up of two 45° cuts.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pressure loss - miter cut pipe or tube
You are correct. This is for exhaust gas at around 650 °F.
Reason I didn't say it was because i was interested in methodoloy, not accuracy at this time.
So, I guess i need to get exh gas density involved in 33 feet to get its pressure loss in PSI?
Am I right?
Actually I need to get it in "inches of water column".
And thank you again for answering.
Mike
RE: Pressure loss - miter cut pipe or tube
http://virtualpipeline.spaces.msn.com
RE: Pressure loss - miter cut pipe or tube
Any hint on how to get "equivalent length"?
I have forgotten most of these that I knew once.
Mike
RE: Pressure loss - miter cut pipe or tube
Which depends a bit on diameter, but most sizes fall closely to 1.25 x the pipe diameter (") = feet of Le for a 45º Ell. And for a 90º ell use 1.5 x diam" = feet Le.
http://virtualpipeline.spaces.msn.com
RE: Pressure loss - miter cut pipe or tube
Should be a 2.5 for standard 90º ells.
http://virtualpipeline.spaces.msn.com
RE: Pressure loss - miter cut pipe or tube
Mike
RE: Pressure loss - miter cut pipe or tube
Head = (ƒML/D + K) x v2/2g
where ƒM is the Moody friction factor. This is equivalent to the ƒT used by Crane 410.
The L/D value of a fitting can therefore be expressed as K/ƒM.
In your example ƒM is about 0.011 and the K value for 2 off 45° miters will be 2 x 0.165 = 0.33. This makes L/D = 0.33/0.011 = 30. Your ID of 2.5 ft (30") makes the equivalent length 30 x 2.5 = 75 ft.
This is identical to the value given by BigInch. The K value using the method of Hooper (Chem Eng, Aug 24, 1981) is 0.34 so I would be fairly confident of this value.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pressure loss - miter cut pipe or tube
If you were working with pipe of a significantly different roughness you would have to calculate the L/D using the method in my previous post, i.e first calculate the K value using the ƒT for commercial steel pipe in the Crane formula, and then convert to equivalent length of your pipe by dividing by the ƒM for your particular conditions.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pressure loss - miter cut pipe or tube
Mike