Short Answer:

The Venturi effect is the phenomenon in which the pressure of a fluid decreases as it flows through a constricted (narrow) section of a pipe, while its velocity increases. It occurs due to the conversion of pressure energy into kinetic energy in accordance with Bernoulli’s principle.

In simple words, when a fluid passes through a narrowing in a pipe, it speeds up and its pressure drops. This effect is widely used in various engineering devices such as Venturi meters, carburetors, aspirators, and atomizers to measure or control fluid flow efficiently.

Detailed Explanation:

Venturi Effect

The Venturi effect is a fundamental concept in fluid mechanics that describes the relationship between the velocity and pressure of a moving fluid when it passes through a constricted region of a pipe. It is named after the Italian physicist Giovanni Battista Venturi, who first studied this phenomenon in the 18th century.

This effect forms the basis for several practical flow measurement and control devices such as Venturi meters, aircraft pitot tubes, carburetors, and vacuum pumps. It plays a crucial role in engineering applications where pressure and velocity changes in flowing fluids must be monitored or utilized.

1. Principle of Venturi Effect

The Venturi effect is explained using Bernoulli’s principle, which states that the total mechanical energy of a fluid (the sum of its pressure energy, kinetic energy, and potential energy) remains constant along a streamline for an incompressible, frictionless flow.

Mathematically,

Here,

•  = pressure intensity (N/m²)
•  = density of the fluid (kg/m³)
•  = velocity of the fluid (m/s)
•  = acceleration due to gravity (m/s²)
•  = elevation head (m)

When a fluid enters a narrow section (throat) of a pipe, the cross-sectional area decreases. According to the continuity equation:

where   and   are the areas, and   and   are the velocities at the larger and smaller sections respectively.

Since  , it means  .
Thus, as velocity increases in the throat, the fluid pressure decreases — this is the Venturi effect.

2. Explanation Using Energy Conversion

The Venturi effect occurs because of the conversion of pressure energy into kinetic energy.

• When the fluid enters the constricted section, its velocity must increase (to satisfy continuity).
• According to Bernoulli’s principle, since total energy is conserved, the increase in velocity results in a decrease in pressure.
• As the fluid leaves the throat and the pipe widens again, the velocity decreases and the pressure partially recovers.

Hence, the Venturi effect shows the trade-off between velocity and pressure in a flowing fluid.

3. Mathematical Representation

From Bernoulli’s and continuity equations:

At two points — one before the throat (1) and one at the throat (2), we can write:

And from the continuity equation:

Combining these two equations gives the relationship between pressure difference and velocity:

This pressure difference   can be measured using a differential manometer, and it forms the working principle of a Venturi meter.

4. Physical Explanation

When fluid flows through a converging section of a pipe, its speed increases because the same volume of fluid must pass through a smaller area per unit time. As speed increases, pressure drops due to the energy conversion (pressure energy → kinetic energy).

At the throat (narrowest section), velocity is maximum and pressure is minimum.

When the fluid moves into the diverging section, the velocity decreases and the pressure increases again. However, due to frictional losses, the pressure at the outlet is slightly less than at the inlet.

This pressure drop in the throat region is the characteristic feature of the Venturi effect.

5. Applications of Venturi Effect

The Venturi effect has a wide range of practical applications in mechanical and aeronautical engineering:

1. Venturi Meter:
   It measures the flow rate of fluids in pipelines. The pressure difference between the wide and narrow sections helps calculate discharge accurately.
2. Carburetors in Internal Combustion Engines:
   In carburetors, the air passing through a Venturi throat draws fuel from a jet due to the low pressure created by the Venturi effect, mixing air and fuel properly.
3. Atomizers and Sprayers:
   Perfume bottles, insect sprayers, and paint guns use the Venturi effect to draw and atomize liquid into fine droplets as air passes through a narrow nozzle.
4. Aspirators and Vacuum Pumps:
   The effect is used to create suction or vacuum in devices like laboratory aspirators by generating low pressure through a constricted passage.
5. Aircraft Pitot Tubes and Venturi Tubes:
   Used to measure airspeed in aircraft and air pressure differences, helping in navigation and altitude control.
6. Water Ejectors and Jet Pumps:
   The Venturi principle is used in these devices to move or lift fluids using the pressure drop caused by a fast-moving fluid stream.

6. Importance in Engineering

• The Venturi effect allows engineers to measure velocity, flow rate, and pressure changes in a fluid system.
• It demonstrates the energy conservation and pressure-velocity relationship in fluid flow.
• It helps in designing efficient pumps, nozzles, and flow meters.
• It is crucial in aerodynamics, helping explain lift generation on aircraft wings and air movement in ducts.

7. Limitations of Venturi Effect

While very useful, the Venturi effect has certain limitations:

1. It is accurate only for steady, incompressible, and non-viscous flows.
2. Friction losses in real fluids cause errors.
3. For compressible fluids (like gases), density changes affect accuracy.
4. Precise machining and alignment of the constriction are necessary for accurate results.

Conclusion

In conclusion, the Venturi effect is the phenomenon where a fluid’s velocity increases and pressure decreases as it passes through a constricted section of a pipe. It is a direct consequence of Bernoulli’s principle and continuity equation, showing the conversion of pressure energy into kinetic energy. The Venturi effect is applied in many practical devices, including Venturi meters, carburetors, atomizers, and jet pumps, making it one of the most important principles in fluid mechanics and engineering design.