Pipe Sizing Basics. Major & Minor Losses Under Supervision of: Prof . Dr. Mahmoud Fouad By students : Mahmoud Bakr 533 Mohammed Abdullah 511 Moaz Emad 619 Mohammed Nabil Abbas 525. Applications . How big does the pipe have to be to carry a flow of x m 3 /s?.
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Major & Minor Losses
Under Supervision of:
Prof. Dr. Mahmoud Fouad
Mahmoud Bakr 533 Mohammed Abdullah 511
Moaz Emad 619 Mohammed Nabil Abbas 525
which defines the friction factor, f. f is insensitive to moderate changes in the flow and is constant for fully turbulent flow. Thus, it is often useful to estimate the relationship as the head being directly proportional to the square of the flow rate to simplify calculations.
Reynolds Number is the fundamental dimensionless group in viscous flow. Velocity times Length Scale divided by Kinematic Viscosity. Relative Roughness relates the height of a typical roughness element to the scale of the flow, represented by the pipe diameter, D. Pipe Cross-section is important, as deviations from circular cross-section will cause secondary flows that increase the pressure drop. Non-circular pipes and ducts are generally treated by using the hydraulic diameter, in place of the diameter and treating the pipe as if it were round
For laminar flow, the head loss is proportional to velocity rather than velocity squared, thus the friction factor is inversely proportional to velocity
The familiar Moody Diagram is a log-log plot of the Colebrook correlation on axes of friction factor and Reynolds number, combined with the f=64/Re result from laminar flow. The plot below was produced in an Excel spreadsheet
Obtain the allowable head loss from the Bernoulli equation, then start by guessing a friction factor. (0.02 is a good guess if you have nothing better.) Calculate the velocity from the Darcy-Weisbach equation. From this velocity and the piping characteristics, calculate Reynolds Number, relative roughness and thus friction factor.
Repeat the calculation with the new friction factor until sufficient convergence is obtained. Q = VA
Although they often account for a major portion of the head loss, especially in process piping, the additional losses due to entries and exits, fittings and valves are traditionally referred to as minor losses. These losses represent additional energy dissipation in the flow, usually caused by secondary flows induced by curvature or recirculation. The minor losses are any head loss present in addition to the head loss for the same length of straight pipe.
Like pipe friction, these losses are roughly proportional to the square of the flow rate. Defining K, the loss coefficient, by
. K is the sum of all of the loss coefficients in the length of pipe, each contributing to the overall head loss
Factors affecting the value of K include :
the exact geometry of the component,.
the flow Reynolds number , etc .
diffusor angle ()Some types of minor lossesHead Loss due to Gradual Expansion (Diffuser)
Losses can be reduced by accelerating the flow gradually and eliminating the
Possible separation from wall
Kb varies from 0.6 - 0.9
To calculate losses in piping systems with both pipe friction and minor losses use
Use goal seek or Solver to find discharge that makes the calculated head loss equal the given head loss.
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