This document discusses three flow measurement devices: the venturimeter, orificemeter, and Pitot tube. It explains that a venturimeter and orificemeter both use Bernoulli's theorem to measure flow rates. A venturimeter uses a converging-throat-diverging shape while an orificemeter uses a flat plate with a circular hole. For both, the theoretical flow rate is adjusted using a discharge coefficient to obtain the actual flow rate. A Pitot tube measures flow velocity by finding the pressure at a stagnation point where flow velocity is zero. The theoretical velocity is adjusted using a velocity coefficient to obtain the actual flow velocity.

1. Aldel Education Trust’s
ST. JOHN COLLEGE OF ENGINEERING AND MANAGEMENT, PALGHAR
(ST. JOHN POLYTECHNIC)
DEPARTMENT OF MECHANICAL ENGINEERING
SUB: FLUID MECHANICS AND MACHINERY
TOPIC: VENTURIMETER, ORIFICEMETER &
PITOT TUBE
PREPARED BY:-
Prof. Pranit Mehata
Lecturer, SJCEM
7972064172

2. VENTURIMETER
A venturimeter is one of the most important practical applications of
Bernoulli’s theorem.
It is an instrument used to measure the rate of discharge in a pipeline
Fixed permanently at different sections of the pipeline to know the
discharges there.
A venturimeter has been named after the 18th century Italian engineer
Venturi

3. VENTURIMETER
 Venturimeter may be classified as
follows:
1. Horizontal venturi meters.
2. Vertical venturi meters.
3. Inclined venturi meters.
 A venturimeter consists of the
following three parts:
1. A short converging part,
2. Throat, and
3. Diverging part.

4. VENTURIMETER
 Discharge through the venturimeter is given by
𝑸𝒕𝒉 =
𝑪𝒅𝑨𝟏𝑨𝟐 𝟐𝒈𝑯
𝑨𝟏
𝟐
− 𝑨𝟐
𝟐
 Actual discharge is given by, 𝑸𝒂𝒄𝒕 = 𝑪𝒅 × 𝑸𝒕𝒉
 𝐶𝑑=coefficient of discharge. Its value for venturi meter is 0.98

5. ORIFICEMETER
 Orifice meter or orifice plate is a device employed for
measuring the discharge of fluid through a pipe.
 It also works on the same principle of a venturimeter.
 It is cheaper than venturimeter.
 It consists of a flat circular plate having a circular sharp
edged hole (called orifice) concentric with the pipe.
 The diameter of the orifice may vary from 0.4 to 0.8 times
the diameter of the pipe but its value is generally chosen
as 0.5.
 Section 2-2 is called as Vena-contracta. At this section
area of fluid is minimum, whereas velocity is maximum
and pressure is minimum.
 Maximum pressure drop will occur at vena-contracta.

6. ORIFICEMETER
Discharge through the orifice meter is given by
𝑸𝒕𝒉 =
𝑪𝒅𝑨𝟎𝑨𝟏 𝟐𝒈𝑯
𝑨𝟏
𝟐
− 𝑨𝟎
𝟐
Actual discharge is given by, 𝑸𝒂𝒄𝒕 = 𝑪𝒅 × 𝑸𝒕𝒉
𝐶𝑑=coefficient of discharge. Its value for orifice meter is 0.64

7. PITOT TUBE
 A pitot tube is the simple device used for
measuring the velocity of the flow at the
required point in a pipe or a stream.
 It is also called as impact tube or
stagnation tube.
 It is based on the principle that if the
velocity of flow at a point becomes zero,
the pressure is increased due to
conversion of kinetic energy into pressure
energy

8. PITOT TUBE
Velocity of fluid through the pitot tube is given by
𝑽𝒕𝒉 = 𝟐𝒈𝒉
Actual velocity is given by, 𝑽𝒂𝒄𝒕 = 𝑪𝑽 × 𝑽𝒕𝒉
𝐶𝑉=coefficient of velocity. Its value varies from 0.95 to 1.

9. HYDARULIC COEFFIECIENTS
 Coefficient of Discharge (𝑪𝒅): The ratio of actual discharge to the theoretical discharge.
𝑪𝒅 =
𝑸𝒂𝒄𝒕
𝑸𝒕𝒉
 Coefficient of Contraction (𝑪𝒄): The ratio of area of vena contracta to the area of the orifice.
𝑪𝒄 =
𝑨𝟐
𝑨𝟎
 Coefficient of Velocity (𝑪𝑽): The ratio of the actual velocity of fluid to the theoretical velocity.
𝑪𝑽 =
𝑽𝒂𝒄𝒕
𝑽𝒕𝒉
𝑪𝒅 = 𝑪𝒄 × 𝑪𝒗