Pressure drops in elbows
Pressure drops in elbows
(OP)
Why the 90 degrees short-radius elbows create a larger pressure drop inside the line, then the 90 degrees long-radius elbows?Could this be illustated by a mathematical equation?
Is there any difference in pressure drops between the 45 degrees elbows and the 90 degrees long-radius elbows?
Is there any difference in pressure drops between the 45 degrees elbows and the 90 degrees long-radius elbows?





RE: Pressure drops in elbows
m777182
RE: Pressure drops in elbows
1-the loss due to curvature
2-the excess loss in downstream tangent
3-the loss due to length
I understand 1 and 3. Can someone explain 2?
Good luck,
Latexman
RE: Pressure drops in elbows
I have one customer that thought they needed long sweep elbows for their high viscosity product, BUT in reality the high viscosity required such a large diameter tube to keep the pressure loss down that our line velocity was so slow (less than .7 fps) it didn't matter.
RE: Pressure drops in elbows
It's been well over a decade since I've had courses in all this, so I'll just rely on memory, and common sense.
It sounds like "downstream tangent" is referring to the point at which the flow regime changes - the bend transitions back into a straight run, or into a diffent degree of curvature. Any transition of fluid flow will introduce turbulence. Turbulence will lead to losses which are independent of other losses.
Does that sound good?
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve
RE: Pressure drops in elbows
Good luck,
Latexman
RE: Pressure drops in elbows
From a practical point of view, at least with regard to contemporary ductile iron pipe and fittings for water and sewer applications, there is normally very little if not insignificant minor head loss with contemporary bend fittings, at even say a 90 degree ell location, with all this being considered. In testing some time ago at the flow facility at Utah State University, a 24” (~600mm) 90 degree ANSI/AWWA C153/A21.53 (“compact” design) latest configuration ell fitting/pipe assembly with standard cement mortar lining manufactured by ACIPCO was found to have an overall (including expansion and contraction pipe end connection effects) effective minor loss coefficient value slightly less than 0.7. I believe this value, that equates to a headloss of less a tenth of a psi at a flow velocity of 3 ft/sec (~1 m/sec) based on the relationship HL=KsV^2/(2G), may be compared to the following traditional references for prior ell minor head loss coefficients:
1. K Factor .90 Reference “Civil Engineering Reference Manual”, 7th Ed., Michael Lindbergh, Professional Publications, pg 17-12, Table 17.4
2. K Factor .9 Reference “Fluid Mechanics”, 7th Ed., Wylie & Streeter, McGraw Hill. Pg 245, Table 5.3
3. K Factor .9 Reference Water Resources and Environmental Engineering, 3rd Ed., Linsley & Franzini, Mc-Graw Hill, pg. 282, Table 11-2e
4. K Factor .75 Reference Manual of British Water Supply Practice, Institution of Water Engineers, Heffer & Sons Ltd., pg. 147, Table XXVII