this presentations describes two fluid flow measuring instruments, pitot tube and current meter.

1. Fluid Flow Measuring
Instruments
Guided by: Mr. Kartik Ayer
Prepared by: Gaurav Dave(130990136011)

2. Contents
 Pitot tube
 Introduction
 Working principle
 Construction and working
 Types of Pitot tube
 Applications
 Current meter
 Introduction
 Working principle
 Construction and working

3. Pitot Tube

4. • Pitot tube was invented by the French engineer Henri Pitot in the early 18th
century.
• Pitot tube is a pressure measurement instrument used to measure fluid flow
velocity.
• It is used for measuring the velocity of liquid flow at any point in a pipe or a
channel.

5. Working principle of Pitot tube
• “If the velocity of flow at a point becomes zero, the pressure is increased
there due to the conversion of the kinetic energy into pressure energy.”
• The point at which the velocity of flow becomes zero is called stagnant
point.
• The pressure at stagnant point is called total pressure or head or stagnation
pressure.

6. Construction and working

7. • Pitot tube consists of L-shaped glass tube, a tube bent at 90o and with the
ends unsealed.
• The horizontal part is called ‘body’ and the vertical is called ‘stem’.

8. Construction and working
• p1 = pressure at point (1)
• V1 = velocity at point (1)
• P2 =pressure at point (2)
• V2 = velocity at point (20
• H = depth of tube in liquid
• h = rise of liquid above the free surface
of liquid in tube

9. Velocity measurement and Coefficient of pitot
tube
• Applying Bernoulli’s equation at
point (1) and (2),
•
𝑝1
𝜌𝑔
+
𝑉1
2
2𝑔
+ 𝑧1 =
𝑝2
𝜌𝑔
+
𝑉2
2
2𝑔
+ 𝑧2
Datum head z1 = z2
V2 = 0
Therefore,
𝑝1
𝜌𝑔
= H &
𝑝2
𝜌𝑔
= H + h
𝑉1
2
2𝑔
= h
Thus V1 = 𝟐𝒈𝒉
The above equation gives the
theoretical velocity at point (1)
Actual velocity,
V1act = Cv 𝟐𝒈𝒉

10. Continued…
The above equation gives the
theoretical velocity at point (1)
Actual velocity,
V1act = Cv 𝟐𝒈𝒉
Where Cv is the Coefficient of pitot
tube
Cv  0.96 to 0.99

11. Stagnation or Total Head
It is the sum of static head and dynamic head. • Total head:
𝑝1
𝜌𝑔
+
𝑉1
2
2𝑔
=
𝑝2
𝜌𝑔
• Total pressure at point (1):
= static + dynamic pressure
p1 = p2 –
𝑉1
2
2
⍴
• Total pressure at point (2):
p2 =
𝑉1
2
2
⍴ + p1

12. Static pressure
“ It is defined as the pressure of liquid
measured when the liquid is static”.
h1 = static pressure head
h2 = dynamic pressure head
Total pressure head = h1 + h2

13. Types of Pitot tube

14. Pitot tube with piezometer raised in flow through pipe

15. Pitot tube with differential
manometer
Here,
V1 = Cv 2𝑔ℎ
h = x[
⍴ 𝐻𝑔
⍴ 𝑝𝑖𝑝𝑒
- 1]
X = Differential manometer reading in
mm of mercury
⍴ 𝑝𝑖𝑝𝑒 = Density of liquid flow through
pipe

16. Pitot static tube
h = x[
⍴ 𝐻𝑔
⍴ 𝑝𝑖𝑝𝑒
- 1]
h in meter of liquid flow in channel or
through pipe

17. Applications

18. • In industry, the flow velocities being measured are often those flowing in
ducts and tubing where pitot tube is useful.
• In weather stations with high wind speeds.

19. Current Meter

20. • The Current meter is a device used to measure the velocity of water in rivers
and in open channels.
• The current meter consists of hollow hemisphere or cups mounted on
spokes so as to cause rotation about a shaft perpendicular to the direction of
flow.

21. Principle

22.  Mechanical
• Mechanical current meters are mostly
based on counting the rotations of a
propeller.
 Acoustic
• Doppler effect is used. It use a ceramic
transducer to emit a sound into the
water.
 Electromagnetic Induction
• Charged particles (the ions in seawater)
are moving with the ocean currents in
the magnetic field of the Earth which is
perpendicular to the movement.
• Using Faraday's law of induction , it is
possible to evaluate the variability of the
averaged horizontal flow by measuring
the induced electric currents.
 Tilt
• Tilt current meters operate under the
drag-tilt principle. They consist of a sub-
surface buoy that is anchored to the sea
floor with a flexible line or tether.

23. Construction and working

24. • The entire setup is lowered into water from a
bridge or a boat.
• The drag on a hollow hemisphere or cups is
greater when its open side faces the liquid stream
and so there is a net torque on assembly when
flow comes from any direction in the plane of
rotation.
• This rotation is converted into electrical signal by
means of a circuit.
• A fixed number of revolutions of wheel produce
a beat that can be heard clearly.
• The number of beats in a given period of time is a
function of fluid velocity.

25. References
• Fluid Mechanics: Basic Concepts & Principles, Shiv Kumar
• http://www.sciencedaily.com/releases/2010/09/100914102112.htm
• http://www.aoml.noaa.gov/phod/floridacurrent/background.php