Pressure drop in bends when pumping viscous fluids
Pressure drop in bends when pumping viscous fluids
(OP)
Hi!
I have little prior knowledge of reology, but I have now come across a problem where I need to calculate the pressure drop in a pipe bend. The fluid is tomato paste (approximately power-law) so the flow will always be laminar.
Is it correct to assume that the pressure drop in a bend is proportonal to the pressure drop in an equvalent straight pipe of the same length? Is there a way I can calculate the proportion factor from angle, pipe diameter and bend diameter?
I do not ask for one-time resistance coefficients, but for a more general solution.
Your help will be most appreciated.
Regards
Rasmus Ågren
I have little prior knowledge of reology, but I have now come across a problem where I need to calculate the pressure drop in a pipe bend. The fluid is tomato paste (approximately power-law) so the flow will always be laminar.
Is it correct to assume that the pressure drop in a bend is proportonal to the pressure drop in an equvalent straight pipe of the same length? Is there a way I can calculate the proportion factor from angle, pipe diameter and bend diameter?
I do not ask for one-time resistance coefficients, but for a more general solution.
Your help will be most appreciated.
Regards
Rasmus Ågren





RE: Pressure drop in bends when pumping viscous fluids
Pressure loss will depend on radius of bends, pipe ID, roughness, etc.
If you need to calculated pressure loss, I would suggest using one of the piping software.
RE: Pressure drop in bends when pumping viscous fluids
Most methods use equivalent length equations, but in fact these are incorrect for laminar flow. The method that I like is the '2k method' published in an 1981 article:
The two-K method predicts head losses in pipe fittings
W.B. Hooper
Chemical Engineering, Aug 1981
Pages 96 to 100
Just as in a straight pipe the friction in a bend increases at low Reynolds numbers. At high Reynolds the curve goes horizontal. The formula's are used in a web based calculation routine on h
This only takes care of the laminar flow, it doesn't do anything with the rheology - but it is certainly a lot more accurate than the usual fixed k method.
Regards, Wim
RE: Pressure drop in bends when pumping viscous fluids
A good reference that describes piping calculations in food processing is Prof JF Steffe's book, which is available for download at http://www.egr.msu.edu/~steffe/
See pages 128-136
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pressure drop in bends when pumping viscous fluids
Regards
Rasmus Ågren
RE: Pressure drop in bends when pumping viscous fluids
My apology. I misread your OP.
Yes, a bend is usually treated by an "equivalent length".
I was thinking you said somthing along the lines of a 8" bend being modelled by an 8" length of straight pipe.
Sorry about that.