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![• Analytical expression of K - If the velocity v1 < 1.2 m/s or 4
ft/s, the K values can be given as :
K = [ 1-(A1/A2) ]² = [ 1-(D1/D2)² ]²
• As previous table consist of practical values therefore
theoretical formulas are different for different values &
above mentioned formula is applicable at 1.2 m/s velocity.](https://image.slidesharecdn.com/headlosses-150610074408-lva1-app6891/85/Head-losses-23-320.jpg)
![• Analytical expression of K - If the velocity v1 < 1.2 m/s or 4
ft/s, the K values can be given as :
K = [ 1-(A1/A2) ]² = [ 1-(D1/D2)² ]²
• As previous table consist of practical values therefore
theoretical formulas are different for different values &
above mentioned formula is applicable at 1.2 m/s velocity.](https://image.slidesharecdn.com/headlosses-150610074408-lva1-app6891/75/Head-losses-23-2048.jpg)
Uploaded byFaizan Shabbir
Head losses
The document discusses head loss in fluid systems, detailing its types, causes, and the equations used to calculate it, such as the Darcy-Weisbach equation. It explains the difference between major losses (friction losses in pipes) and minor losses (due to fittings and other elements), including their contributions to overall energy loss during flow. Key concepts such as kinetic head, potential head, and the effects of turbulent versus laminar flow are also outlined.
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Head losses
- 2. • Danial ZafarGondal 13-ME-027 • Ehtisham Qaiser 13-ME-031 • Faizan Shabbir 13-ME-032 • Asif Mehboob 13-ME-034 6/10/2015 2 Group Members
- 3. 6/10/2015 3 • Definition •Dimensional Analysis • Types • Darcy Weisbech Equation • Major Losses • Minor Losses • Causes Head Losses
- 4. • Head lossis loss of energy per unit weight. • Head = Energy of Fluid / Weight • Head losses can be – Kinetic Head – Potential Head – Pressure Head 6/10/2015 4Danial Gondal Head Loss
- 5. • Kinetic Head –K.H. = kinetic energy / Weight = v² /2g • Potential Head – P.H = Potential Energy / Weight = mgz /mg = z • Pressure Head – P.H = P/ ρ g 6/10/2015 5
- 6. • (P/ ρg) + (v² /2g ) + (z) = constant • (FL-2F-1L3LT-2L-1T2) + (L2T-2L1T2)+(L) = constant • (L) + (L) + (L) = constant • As L represent height so it is dimensionally L. 6/10/2015 6 Dimensional Analysis
- 7. • However theequation (P/ ρ g) + (v² /2g ) + (z) = constant Is valid for Bernoulli's Inviscid flow case. As we are studying viscous flow so (P1/ ρ g) + (v1² /2g ) + (z1) = EGL1(Energy Grade Line At point 1) (P2/ ρ g) + (v2² /2g ) + (z2) = EGL2(Energy Grade Line At point 2) 6/10/2015 7 Head Loss
- 8. • For InviscidFlow EGL1 - EGL2= 0 • For Viscous Flow EGL1 - EGL2= Hf 6/10/2015 8 Head Loss
- 9.
- 10. •Friction loss isthe loss of energy or “head” that occurs in pipe flow due to viscous effects generated by the surface of the pipe. • Friction Loss is considered as a "major loss" •In mechanical systems such as internal combustion engines, it refers to the power lost overcoming the friction between two moving surfaces. •This energy drop is dependent on the wall shear stress (τ) between the fluid and pipe surface. 6/10/2015 10 Friction Loss
- 11. •The shear stressof a flow is also dependent on whether the flow is turbulent or laminar. •For turbulent flow, the pressure drop is dependent on the roughness of the surface. •In laminar flow, the roughness effects of the wall are negligible because, in turbulent flow, a thin viscous layer is formed near the pipe surface that causes a loss in energy, while in laminar flow, this viscous layer is non-existent. 6/10/2015 11 Friction Loss
- 12. Frictional head lossesare losses due to shear stress on the pipe walls. The general equation for head loss due to friction is the Darcy-Weisbach equation, which is where f = Darcy-Weisbach friction factor, L = length of pipe, D = pipe diameter, and V = cross sectional average flow velocity. This equation is valid for pipes of any diameter and for both laminar and turbulent flows. 6/10/2015 12 Friction Loss
- 13. For Laminar Flow 6/10/201513 Friction Loss For Turbulent Flow
- 14.
- 15. • In additionto head loss due to friction, there are always other head losses due to pipe expansions and contractions, bends, valves, and other pipe fittings. These losses are usually known as minor losses (hLm). • In case of a long pipeline, the minor losses maybe negligible compared to the friction losses, however, in the case of short pipelines, their contribution may be significant.
- 16. • Losses causedby fittings, bends, valves, etc…
- 17. • Minor incomparison to friction losses which are considered major. • Losses are proportional to – velocity of flow, geometry of device. HL = K (v² /2g) • The value of K is typically provided for various devices. • Energy lost – units – m or ft • K - loss factor - has no units (dimensionless).
- 18. where , HLm =minor loss K = minor loss coefficient V = mean flow velocity g V KhLm 2 2 Type K Exit (pipe to tank) 1.0 Entrance (tank to pipe) 0.5 90 elbow 0.9 45 elbow 0.4 T-junction 1.8 Gate valve 0.25 - 25 Typical K values Minor Losses Are Due to
- 19. • As fluidflows from a smaller pipe into a larger pipe through sudden enlargement, its velocity abruptly decreases; causing turbulence that generates an energy loss. • The amount of turbulence, and therefore the amount of energy, is dependent on the ratio of the sizes of the two pipes. Sudden Enlargement
- 20. • Energy lostis because of turbulence. Amount of turbulence depends on the differences in pipe diameters. HL = K (v² /2g) • The values of K have been experimentally determined and provided in Figure and Table
- 23. • Analytical expressionof K - If the velocity v1 < 1.2 m/s or 4 ft/s, the K values can be given as : K = [ 1-(A1/A2) ]² = [ 1-(D1/D2)² ]² • As previous table consist of practical values therefore theoretical formulas are different for different values & above mentioned formula is applicable at 1.2 m/s velocity.
- 24. • Decrease inpipe diameter Note that the loss is related to the velocity in the second (smaller) pipe! Sudden Contraction
- 25. • The sectionat which the flow is the narrowest – Vena Contracta •At vena contracta, the velocity is maximum.
- 26. Energy lossesfor sudden contraction are less than those for sudden enlargement.
- 27.
- 28. • Again agradual contraction will lower the energy loss (as opposed to sudden contraction). θ is called the cone angle. Gradual Contraction
- 29. • Case ofwhere pipe enters a tank – a very large enlargement. • The tank water is assumed to be stationery, that is, the velocity is zero. • Therefore all kinetic energy in pipe is dissipated, therefore K =1.0 Exit Loss
- 30. • If theenlargement is gradual (as opposed to our previous case) – the energy losses are less. • The loss again depends on the angle of enlargement. Gradual Enlargement
- 31. Fluid moves fromzero velocity in tank to v². Entrance Losses
- 32.
- 33. Head loss hasseveral causes, including: • Losses depend on the conditions of flow and the physical properties of the system. • Movement of fluid molecules against each other • Movement of fluid molecules against the inside surface of a pipe or the like, particularly if the inside surface is rough, textured, or otherwise not smooth • Bends and other sharp turns in piping 6/10/2015 33 Causes
- 34. In pipe flowsthe losses due to friction are of two kinds: • Skin-friction – This is due to the roughness of the inner part of the pipe where the fluid comes in contact with the pipe material • Form-friction – It is due to obstructions present in the line of flow perhaps a bend, control valve, or anything that changes the course of motion of the flowing fluid. 6/10/2015 34 Causes
- 35. THANK YOU… ANY QUESTIONPLEASE ……??? 6/10/2015 35