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Lesson 23 HEAD LOSS

Lesson 23 HEAD LOSS. DEFINE the terms head loss, frictional loss, and minor losses. DETERMINE friction factors for various flow situations using the Moody chart. CALCULATE the head loss in a fluid system due to frictional losses using Darcy’s equation.

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Lesson 23 HEAD LOSS

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  1. Lesson 23HEAD LOSS • DEFINE the terms head loss, frictional loss, and minor losses. • DETERMINE friction factors for various flow situations using the Moody chart. • CALCULATE the head loss in a fluid system due to frictional losses using Darcy’s equation. • CALCULATE the equivalent length of pipe that would cause the same head loss as the minor losses that occur in individual components.

  2. Head Loss • A measure of the reduction in the total head (sum of elevation head, velocity head and pressure head) of the fluid as it moves through a fluid system. • Unavoidable in real fluids. • Caused by • Friction between the fluid and the walls of the pipe • Friction between adjacent fluid particles as they move relative to one another; • Turbulence caused whenever the flow is redirected • Frictional loss - That part of the total head loss that occurs as the fluid flows through straight pipes.

  3. Head loss is directly proportional to • the length of pipe, • the square of the fluid velocity, • the friction factor. • The head loss is inversely proportional to the diameter of the pipe

  4. Friction Factor • Depends on • Reynolds number • Relative roughness of the pipe’s inner surface • Obtained from the Moody Chart

  5. Darcy’s Equation • Used to calculate frictional head loss • Two forms • Losses in the system associated with the length of the pipe. • “Minor” losses

  6. Frictional Head Loss where: f = friction factor (unitless) L = length of pipe (ft) D = diameter of pipe (ft) v = fluid velocity (ft/sec) g = gravitational acceleration (ft/sec2)

  7. Minor Losses • Losses in pipelines due to • Bends, • Elbows • Joints • Valves • Often more important than the losses due to pipe friction • For turbulent flow, the head loss varies as the square of the velocity. • Expressed by means of a loss coefficient (k)

  8. Equivalent Pipe Length • Found by setting the two forms of Darcy’s Equation equal to each other and solving for L to get • Can also solve for k to get

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