Minor Losses. Gunther Anderson Ryan Barr Risa Benvenga

Transcription

1 Minor Losses Gunther Anderson Ryan Barr Risa Benvenga

2 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

3 Minor Loss Equation Total minor head loss is determined as follows: K values vary based on the component s geometry and physical properties

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

5 Types of Minor Losses Inlet and Exit Transitions Expansion and Contraction Bends and Elbows Tees Valves Pipe Connections and Fittings

6 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

7 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

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

9 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

10 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

11 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

12 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

13 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

14 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

15 Tips for Reducing Head Loss Excessive head loss will result in unnecessary cost burdens for system operators 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

16 Minor Loss Example 1

17 Minor Loss Example 2

18 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

19 References Cruise, James F., M. M. Sherif, and V. P. Singh. "8.4 Minor Losses in Pipes." Elementary Hydraulics. Mason, OH: Cengage Learning, Print. "Head Loss Coefficients." Vano Engineering. N.p., 30 Dec Web. 19 Oct <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, Print. "Fluid Flow through Real Pipes." Pump-House, University of California, Santa Barbara (2004): n. pag. Web. - pg. 17 Gabryjonczyk, R. Reducing Head Loss in Sludge Pumping Applications. Water World. N.p. Web. <