venturi meter

Venturi Meter: Definition, Parts, Working Principle, Derivation, Applications [With PDF]

Amrit Kumar Fluid Mechanics Hydraulic Machines 2 Comments

The Venturi Meter is invented by an American Engineer Clemans Herchel (1841-1932) and named him after Italian Giovanni Venturi (1842-1932).

Venturi Meter is a device or component which is used for measuring the rate of flow of liquid through pipes.

It works on the basic principle of Bernoulli’s Equation.

Bernoulli’s Equation: In Simple language, this is defined as the sum of Pressure energy, Kinetic energy per unit volume and Potential energy per unit volume equal in the same direction.

flow of water in venturi meter

Definition of Venturi Meter:

Venturi Meter is a device in which pressure energy is converted into kinetic energy and It used for measuring the flow rate (Discharge) of the system.

Parts of Venturi Meter:

A Venturi Meter is consisted of:

  • Converging cone or Diameter (the area is decreasing)
  • Throat Diameter (the area is constant)
  • Diverging cone (the area is increasing)

let’s consider a pipe in which there is a venturi meter is fixed. In the pipe fluid is flowing so first it enters into a converging cone then Thorat and then Diverging Cone.

Converging cone:

When water flowing through this cone the area is decreasing, therefore, the speed of flowing water increases and pressure decreases.

Throat Diameter:

When water flowing through this cone the area remains constant therefore the speed of flowing water and pressure remains constant.

Diverging cone:

When water flowing through this cone the area is increasing, therefore, the speed of flowing water decreases and pressure decreases.

diagram of venturi meter
1: Pressure at Inlet, 2: Pressure at Throat (P1 is Greater than P2), 3: Converging Section, 4: Diverging Section, 5: Outlet Pipe

Working Principle of Venturi Meter:

As I already told that Venturi Meter works on Bernoulli’s Principle, so let’s find out how it works?

Suppose quantity of liquid v1 enter to the pipe, as per continuity equation volume flow rate at inlet (Q1), is equal to discharge at outlet (Q2), so if v1 amount of water enters to the inlet of the venturi meter the same amount of water should be discharged at outlet, that means at unit second v1/t1=v2/t2.

As the area of section 1 (according to the above diagram) is more than area of the section , that means due to the decrease area the pressure at throttling section is decreased and velocity will be increased to maintain the flow (Q1=Q2)

In the throat position, the velocity of flow is maximum and pressure is minimum.

After throttling there again a diverging section (diffuser) in section 4 which restores the pressure as nearly possible to the actual value.

By this, we can easily determine the volume flow rate with the help of the U-Tube Manometer, by finding the pressure difference between section 1 (converging section) and section 2 which is throat.

Derivation of Discharge:

The derivation has been solved on paper because their several rotations cannot be typed here.

In the figure, the water flowing in the pipe (flow in) comes with section 1 and flow out goes with section 3.

The several rotations are:

  • A1 = Inlet area in m2.
  • D1 = Diameter of Inlet.
  • D2 = Diameter of the throat.
  • A2 = Throat area in m2.
  • P1 = Pressure at the inlet in N/m2.
  • P2 = Pressure at the throat in N/m2.
  • V1 = Velocity at inlet in m/sec
  • V2 = Velocity at throat in m/sec.
  • h = Pressure heads.
  • Cd = Coefficient of Discharge. This is unitless.
  • Qact= Actual discharge in m3/sec.
  • Qthe= Theoretical discharge in m3/sec.
Venturi Meter derivation
venturi Meter discharge

The other way to find h (Pressure heads) by using differential U–Tube Manometer:

The liquid in the manometer is heavier than the flowing fluid in the pipe.

  • Sh =Specific gravity of the heavier liquid.
  • x = Difference of the heavier liquid column in U-tube
  • S0 =The Specific gravity of flowing fluid.
  • Sl =Specific gravity of the lighter liquid.

h = x [ (Sh / S0) – 1]

The liquid in the manometer is lighter than the flowing fluid in the pipe.

h = x [1- (Sl / S0) ]

Applications of Venturi Meter:

Venturi Meter is used in various field like:

  • Calculating the flow rate of fluid that is Discharge in the pipe.
  • Plumbing.
  • Carburetor.
  • The flow of chemicals in pipelines.
  • This is widely used in large-diameter pipes such as found in the waste treatment process.
  • Also used in the medicine department for the measure, the flow rate of blood in arteries.
  • This also used where high-pressure recovery is required.

Advantages of Venturi Meter:

The advantages of Venturi Meter are:

  • Power loss is very less.
  • This can be used where a small head is available.
  • High reproducibility (the extent to which consistent results are obtained when an experiment is repeated).
  • Accuracy is high over wide flow ranges.
  • This can also be used for a compressible and incompressible fluid.
  • This device is easy to operate.
  • The coefficient of discharge (Cd ) for the venturi meter is high.
  • This is widely used for a high flow rate (Discharge).

Disadvantages of Venturi Meter:

Although there are few disadvantages of Venturi Meter, and those are:

  • The installation cost of a venturi meter is high.
  • There are little difficulties while maintenance.
  • This device can not be used where the pipe has a small diameter of 76.2 mm.
  • Non-linear.
  • This system occupies more space as compared to the orifice meter.
  • It has a limitation of the lower Reynolds number of 150,000.
  • It is expensive and a little bulky.

So this is all about Venturi Meter, I hope you understand the concept of venturi meter.

If you still have doubts feel free to mention in the comment section or you can also use our community portal to ask your question.

In the meantime don not forget to share this article on your favorite social media.

Till then bye-bye, cheers.

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Some FAQ:

What is Venturi Meter?

The Venturi Meter is invented by an American Engineer Clemans Herchel (1841-1932) and named him after Italian Giovanni Venturi (1842-1932). Venturi Meter is a device or component which is used for measuring the rate of flow of liquid through pipes.

What is the use of Venturi meter?

Venturi Meter is used for measuring the flow rate inside the pipe.

What is the Bernoulli’s Principle?

In Simple language, this is defined as the sum of Pressure energy, Kinetic energy per unit volume and Potential energy per unit volume equal in the same direction.

References (External Links):

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About the Author

Amrit Kumar

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Amrit is a Co-founder of Learn Mechanical Portal (Previously owned "Engramritkumar.com"). He completed his diploma in Mechanical Engineering from Acharya Polytechnic Bangalore and also completed his B-Tech from Delhi. Amrit is now preparing for Govt. exams. If you need help, you can ask him regarding any suggestions in the mechanical engineering field. He loves to meet new people.

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