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 component’s 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. <https://vanoengineering.wordpress.com/2012/12/30/head-loss-coefficients/>.

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.waterworld.com/articles/wwi/print/volume-28/issue-2/editorial-focus/technical-notes--pumps/reducing-head-loss-in-sludge-pumping.html>