minor losses -...
TRANSCRIPT
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>