This document provides information about two instruments used to measure fluid flow: the Pitot tube and current meter. It describes the Pitot tube's invention, working principle, construction, types, and applications for measuring flow velocity. The current meter works by counting the rotations of a propeller placed in flowing water. It can also use acoustic Doppler effects, electromagnetic induction, or operate under drag-tilt principles. Both instruments are used to measure liquid flow velocities in pipes, channels, rivers, and oceans.

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