The document discusses flow measurement techniques using a Venturi meter, orifice meter, and Pitot tube in environmental engineering. It outlines the working principles, characteristics, formulas, and applications of each device, highlighting the advantages and limitations of each flow measuring instrument. The Venturi meter is noted for its accuracy, while the orifice meter is more cost-effective for smaller pipelines, and the Pitot tube is utilized to measure fluid velocity in various industrial applications.

1. Government Engineering College
Valsad
( )
:SUBJECT:
Flow measurment using pitot tube, venturi
meter & pipe orifices
Department:-
Environmental Engineering
Guided by:-
Pro. Dhruti Patel

2. •Prepared by:-
1) Bhadani Ashishkumar J. 160190113003
2) Butani Henil R. 160190113006
3) Dankhara Nirmalbhai D. 160190113009
4) Patel Smit P. 160190113040

3. Venturimeter
 It’s Device, used to measure the rate of flow of
fluid through a pipe.
 The equation is based on the Bernoulli equation,
conservation of energy, and the continuity
equation.
 It consists of:
1.Inlet section
2.Convergent Section
3.A cylindrical throat
4.A gradually divergent cone

4. Venturimeter

5. Working of venturimeter
• The fluid whose flow rate isto be measured enters
the entry section of the venturimeter with a pressure
P1.
• As the fluid from the entry section of venturimeter
flows into the converging section, it’spressure
keeps on reducing and attains a minimum value
P2 when it enters the throat.
• That is,in the throat, the fluid pressure P2 will be
minimum.

6. • The differential pressure sensor attached
between the entry and throat section of
the venturimeter records the pressure
difference(P1-P2) which becomes an
indication of the flow rate of the fluid
through the pipe when calibrated.
• The diverging section has been provided
to enable the fluid to regain it’s pressure
and hence it’skinetic energy. Lesser the
angle of the diverging section, greater is
the recovery.
Working of venturimeter

7. Characteristic of venturimeter
• There isno restriction to the flow down the
pipe.
• They can be manufactured to fit any
required pipe size.
• The temperature and pressure within the
pipe does not affect the meter or its
accuracy.
• There are nomoving parts.
• The accurate shape required of the
inside of the meter makes them
relatively expensive to manufactured.

8. Formula of venturimeter
 Pressure difference (H) : 12.6*h
 Theoretically Discharge:
 Discharge:
 Where, Cd = Co-efficient of Discharge
A1 = Area of inlet of venturimeter
A2 = Area of throat of venturimeter

9. ORIFICE METER
• The venturimeter described earlier is a
reliable flow measuring device.
• Furthermore, it causes little pressure loss.
• For these reasons it is widely used,
particularly for large- volume liquid and gas
flows.
• However this meter is relatively complex to
construct and hence expensive.
• Especially for small pipelines, its cost seems
prohibitive, so simpler devices such as orifice meters
are used.

10. 1
2
x
Direction
of flow
Orifice
Differential manometer
2D D/2 Vena contracta
Discharge in orifice meter

11. ORIFICE METER

12. Discharge in orifice meter
Let d1 = diameter at section 1
p1 = pressure at section 1
v1 = velocity at section 1
A1= area at section1
d2, p2, v2, A2 are the corresponding values at section 2.
Applying Bernoulli’s equations at sections 1 and 2, we get
2 2
2
1 2
g 2g g 2g

p v1 1
 z  
p v2
 z
2 2
2
2 1
2g
 v 2
 v2
  p   p1
z  2
 z  2 1
 g 1  g 2 
   
v1
 h 
v2
2g
 v  2ghv where h is the differential head.

13. Let A0 is the area of the orifice.
Coefficient of contraction, c
C A2
A0
1 2
A1
By continuity equation, we have
A1v1 A2v2
 v 
A0C c v
Hence,
c
A2C2v2
A2
1
2gh
C2
A2
1
v2  2gh  0 c 2
2 v 
1
A2
0
Discharge in orifice meter

14. Thus, discharge, 2
c
C2
A2
1
A0Cc 2gh
Q  A2v2  v2 A0Cc 
1
A0
If Cd is the co-efficient of discharge for orifice meter, which is defined as
2
1
A0
2
2
2
d c
c
c
A2
1
C2
A2
1
C2
A2
1
A2
1
C C
1
A0
1
A0
c C Cd
1
A0
Discharge in orifice meter

15. Hence,
The coefficient of discharge of the orifice meter is much
smaller than that of a venturimeter.
A0 A1 2gh
Q Cd
 A2A2
1 0
Discharge in orifice meter

16. PITOT TUBE
 A pitot tube is a pressure measurement instrument used to measure
fluid flow velocity. The pitot tube was invented by the french engineer
Henri pitot in the early 18th century and was modified to its modern
form in the mid-19th century by french scientist Henry Darcy.
 It is widely used to determine the airspeed of an aircraft, water speed
of about, and to measure liquid, air and gas velocities in industrial
applications. The pitot tube is used to measure the local velocity at a
given point in the flow stream and not the average velocity in the pipe
or conduit.

17. PITOT TUBE

18. Types of Pitot tube

19.  The basic pitot tube consists of a tube pointing
directly into the fluid flow. As this tube contains
fluid, a pressure can be measured; the moving
fluid is brought to rest (stagnates) as there is
no outlet to allow flow to continue.
 This pressure is the stagnation pressure of the
fluid, also known as the total pressure or
(particularly in aviation) the pitot pressure.
 The liquid flows up the tube and when
equilibrium is attained, the liquid reaches a
height above the free surface of the water
stream
Working of Pitottube

20.  Measurement of static pressure in this case is
made at the boundary of the wall (Fig.-1). The
axis of the tube measuring the static pressure
must be perpendicular to the boundary and free
from burrs, so that the boundary is smooth and
hence the streamlines adjacent to it are not
curved. This is done to sense the static pressure
only without any part of the dynamic pressure.
 A Pitot tube is also inserted as shown (Fig.-2) to
sense the stagnation pressure. The ends of the
Pitot tube, measuring the stagnation pressure,
and the piezometric tube, measuring the static
pressure, may be connected to a suitable
differential manometer for the determination of
flow velocity and hence the flow rate.
Cont……..

21. Fig.-1 Fig.-2

22.  In industry, the velocities being measured are
often those flowing in ducts and tubing where
measurements by an anemometer would be
difficult to obtain. In these kinds of
measurements, the most practical instrument to
use is the pitot tube.
 The pitot tube can be inserted through a small
hole in the duct with the pitot connected to a U-
tube water gauge or some other differential
pressure gauge for determining the velocity
inside the ducted wind tunnel. One use of this
technique is to determine the volume of air that is
being delivered to a conditioned space.
Operations: