1. Flow measurement

2. Flow measurement Important variable in plant operation
Measured primarily for determining the amount of fluid flowing

3. Fluid types Less or highly viscous Clear or opaque Clean or dirty
Wet or dry
Erosive or corrosive

4. Fluid flow type Stream line or viscous or laminar Turbulent
Combined viscous or turbulent

5. Fluid flow – steam line Occurs at low velocities
All parts flowing in one direction parallel to walls
Change in cross section means change in direction of flow
Pressure drop ∞ flow velocity

6. Fluid flow - turbulent Liquid behaves as independent entities
Pressure varies with Kinetic energy
Prop. To square of turbulent flow velocity

7. Flow meter Flow measured as a quantity or rate of flow
In terms of weight or flow

8. Types of flow meters Head type meters Rota meter (variable –area type)
Electromagnetic type
Mechanical type
Anemometer
Ultrasonic flow meter
Vortex flow meter

9. Head type flowmeter
Produce a pressure difference when fluid flow is maintained through them
Diff. Pressure propotional to square of flow rate
Uses Bernoulli’s theorem

10. Bernoulli's theorm

11. Bernoulli’s theorm
Pressure head + velocity head + elevation head (at a point) =
pressure head + velocity head + elevation head ( at some other point) + loss due to friction

12. Bernoulli’s theorm For in compressible liquid
Q = EA2 sqrt ( (2gPd)/ ρ)
For compressible liquid
Q = EA2 φ sqrt ( (2gPd)/ ρ1)

13. Head flow meter -types Orifice meter Venturimeter Flow nozzle
Pitot tube

14. Orifice meters

15. Orifice meters Head type meter used for large &medium pipes
Orifice plate- inserted to pipe to create a partial restriction to flow
Pressure before orifice plate rises and pressure after it reduces but velocity increases

16. Pressure differnces

17. Position where velocity is maximum & static pressure is min is known as vena contracta

18. Diff. Pressure calculation

19. Orifice meter
Usually pressure tapping is at a distance D & D/2 for up stream & down stream
D- diameter of pipe
For pipe size 0.05m or more
Orifice to pipe diameter is 0.6

20. Friction & contraction effects are considered
Friction & contraction effects are considered. So new term is incorporated called discharge co-efficient ©
C varies with Reynolds's no.
Q = 2.35 X c d2 E √ (Pd /ρ)

21. Flow measurement

22. Construction
Normal thickness m for pipe with diameter 0.15 m & for larger
Materials used bronze, stainless steel, phosphor bronze, gun metal etc.

23. Orifice plate & flanges

24. Types of orifice plates

25. Types of orifice plate
If fluid contains suspended materials , particles tend to settle down in orifice,- to avoid this- segmented or ccentric type used

26. Advantage
Simple, reliable

27. Disadvantage
Poor accuracy,
poor calibration
maintenance problems

28. Venturi meter

30. Three sections- venturimeter
Converging conical section at up stream
Cylindrical throat- provides a panel for measurement- pressure decreased- flow rate steady
Diverging recovery outlet

32. Principle- Bernoulli's theorm

33. dimensions

34. Throat to diameter ratio 0.25 to 0.75
Discharge co-efficient – 0.9 to 1.0
Made of cast iron, gun metal, stainless steel
May be circular, square or rectangular

35. features Calculation similar to orifice plate
Better than orifice meter

36. Flow nozzle

37. Flow nozzle

38. Flow nozzle Principle- Bernoulli’s theorem Simple
Used in higher velocities, difficult to maintain, costly
Used in gases

39. Pitot tube

40. Pitot tube Cylindrical probe inserted into fluid
Velocity head converted into impact pressure
Diff b/w static pressure & impact pressure- proptional to flow

41. By introduction of pitot tube

42. Pitot tube

44. Features Easy to install No pressure loss
Sensitive to up stream disturbance
Not used for sticky and dirty fluids

45. Thank u