Minor Losses

Gunther AndersonRyan Barr

Risa Benvenga

Introduction

Minor losses result from changes in geometry or added components to a piping system

Minor losses along with major losses are responsible for pressure drops along a pipe

Minor Loss Equation

Total minor head loss is determined as follows:

K values vary based on the components geometry and physical properties

Hydraulic Components

Added components will interrupt the smooth flow of fluid, causing minor losses from flow separation and mixing

Types of Minor Losses

Inlet and Exit Transitions Expansion and Contraction Bends and Elbows Tees Valves Pipe Connections and Fittings

Inlet and Exit Transitions

Shape of the transition greatly affects the KL value

Well-rounded entrances are the most efficient

A vena contracta or necking can occur by the entrance which causes an increase in the velocity at the entrance

Expansions and Contractions Ruling Equations:

or

where Vs is the velocity in the smaller diameter

Head loss is caused by a sudden increase or decrease in the pressure head of the pipe

Expansions and Contractions

The magnitude of this loss is a function of the ratio of the two diameters and its angle to the horizontal.

Bends

Change in direction causes fluid separation from the inner wall

A larger angle causes a greater head loss

The radius of the bend and diameter of the pipe also contribute to the losses

Tees

Converging and separating flows will both cause minor losses due to directional changes

T - shape introduces multiple corners that cause additional mixing and flow separation

Flanged fittings cause less energy resistance than threaded

Valves

Used to control the flow Disruption of flow causes minor losses Fully closed valves halt flow

completely Partially opened valves disrupt flow

more than fully opened valves

Vena Contracta

As diameters change in a hydraulic system (entrance), eddies form from the vena contracta

Energy loss associated with this is due to the recovery of the flow following the vena contracta, as well as the shear force from the eddies

Equivalent Length

The equivalent length of pipe is representative of the frictional loss within a fitting or valve that would produce the same loss due to friction

Equivalent length is determined by the following equation:

Once an equivalent length of pipe is determined, it is added to the actual length of pipe to determine total losses

Pipe Connections and Fittings

Fabrication of ends can cause imperfections such as burrs that will disrupt the flow and head losses

Pipes may be: threaded welded flanged glued

All connections cause head losses if not properly connected or fabricated

Tips for Reducing Head Loss

Replace pipes through the project lifetime: Solids will accumulate along the pipe walls, constricting the diameter and altering surface roughness

Minimize pipe lengths and number of components: Both are directly proportional to head loss

Uniform pipe diameter Operate at design velocity

Flat top taper to avoid gas pockets and pipe blockage

Excessive head loss will result in unnecessary cost burdens for system operators

Minor LossExample 1

Minor LossExample 2

Conclusion

Generally: as you increase flow by 10%, the minor losses increase by 20% All energy losses which occur in hydraulic systems are not solely due to

boundary friction These minor losses cause nonuniformities in the flow path, resulting in

small energy losses due to: changes in pipe diameter, pipe geometry, entrance from a reservoir, exit to a reservoir, or control devices (valves)

The two methods of head loss in a pipe come from friction and minor losses, and minor contains a smaller energy magnitude

References

Cruise, James F., M. M. Sherif, and V. P. Singh. "8.4 Minor Losses in Pipes." Elementary Hydraulics. Mason, OH: Cengage Learning, 2007. 232-35. Print.

"Head Loss Coefficients." Vano Engineering. N.p., 30 Dec. 2012. Web. 19 Oct. 2015. .

Hibbeler, R. C. "10.2 Losses Occurring from Pipe Fittings and Transitions." Fluid Mechanics. N.p.: Pearson Prentice Hall, 2015. 528-33. Print.

"Fluid Flow through Real Pipes." Pump-House, University of California, Santa Barbara (2004): n. pag. Web. http://www.cs.cdu.edu.au/homepages/jmitroy/eng247/sect10.pdf - pg. 17

Gabryjonczyk, R. Reducing Head Loss in Sludge Pumping Applications. Water World. N.p. Web.

http://www.cs.cdu.edu.au/homepages/jmitroy/eng247/sect10.pdf