Forces Due To Pipe Bend And/Or Diameter Changes

[IMG]file:///C:/DOCUME%7E1/srai/LOCALS%7E1/Temp/moz-screenshot-1.jpg[/IMG]When a flowing fluid changes direction, a force will act in the bend. Thrust blocks are used in pipe bends to withstand the forces on the pipe caused by momentum change and unbalanced pressure of the fluid flowing in the pipe. Consider a pipe bend lying in the horizontal plane with or without a diameter change. The resultant force and its direction can be estimated by the equations:

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[link Point to another website Only the registered members can access] where


F = reacting force on bend
α = direction of reacting force with respect to x-axis, anticlockwise +ve
Fx = x-component of force
Fy = y-component of force
Q = average flow rate
θ = angle of pipe bend, -180 to 180, anticlockwise +ve w.r.t. x-axis
D1 = internal pipe internal diameter before bend or size change
D2 = internal pipe internal diameter after before bend or size change
P1 = pressure before bend or size change
P2 = pressure after bend or size change
A1 = area before
A2 = area after
V1 = flow velocity before
V2 = flow velocity after
γ = fluid specific gravity; water = 1
ρ = fluid density


BIBLIOGRAPHY


  • Munson BR, Young DF & Okhiishi TH; Fundamentals of Fluid Mechanics, John Wiley & Sons, Inc., NJ, 2005.
  • Hicks TG; Mechanical Engineering Formulas, Pocket Guide; McGraw Hill, New York, 2003, Chapter 10.