# Venturi effect: Definition, Applications

The Venturi effect is the decrease in fluid pressure that occurs when a fluid passes through a constrained segment. A pitot tube, a horizontal tube with an IJ-shaped tube within, is used to calculate the velocity of a fluid moving through it.

The Venturi effect illustrates how the rate of fluid flow changes in an enclosed system as it enters a narrower channel. Bernoulli’s principle can be used to describe the change in fluid flow rate via a pipeline.

Liquids are substances that have the ability to flow and change shape when stressed. They include gases, liquids, and even some plastic solids. The study of fluid characteristics has always been more difficult than hard solids due to their capacity to flow from one location to another and their non-rigid nature. However, it is because of its exceedingly fluid nature and deformability that numerous significant scientific breakthroughs have been made feasible.

Pumping water and oil, piping them,  building the internal combustion engine, and even current aviation technology all owe their existence to the exploitation of fluid characteristics in some way. Pressure is crucial in this type of transportation.

Giovanni Venturi, an Italian physicist, discovered in 1797 that changing the diameter of a pipe can affect the pressure of the fluid running through it. This is known as the venturi effect.

The Venturi effect illustrates how a fluid’s velocity increases when the cross-section of the container in which it travels decreases. The energy at this higher speed is obtained by lowering the fluid’s static pressure.

According to the Venturi effect, in a situation with constant mechanical energy, the velocity of a fluid traveling through a confined space increases while its static pressure decreases. The effect employs both the continuity concept and the mechanical energy conservation theory.

## Bernoulli’s principle

In fluid dynamics, Bernoulli’s theorem describes the relationship between pressure, velocity, and elevation in a flowing fluid (liquid or gas), where compressibility and viscosity (internal friction) are minimal and the flow is steady, or laminar. Daniel Bernoulli, a Swiss mathematician, was the first to derive it in 1738. The overall mechanical energy of the flowing fluid, which includes gravitational potential energy of elevation, fluid pressure energy, and kinetic energy of fluid motion, remains constant.

So, Bernoulli’s principle describes the relationship between pressure, density, fluid velocity per unit mass, and potential energy (usually merely gravitational) per unit mass in a laminar flow along a particular streamline. For flows along a given streamline, the following equation can be used:

In other words, the constant derived in one part of the system is not the same constant found in the other parts of the system, hence the magnitudes of changes in flow parameters in different systems will differ. The polarity of changes, on the other hand, will be consistent in any system, demonstrating the universality of Bernoulli’s principle.

## Venturi effect

When a fluid traveling through a pipe encounters a constriction or narrowing of the pipe, the velocity of flow increases, resulting in a drop in static pressure. This is known as the Venturi effect. This property was discovered in the nineteenth century by the Italian physicist Giovanni Battista Venturi while doing research on fluid mechanics, and it is still used today as one of the most frequent techniques of measuring velocity (Venturi tube).

Venturi effect

## Bernoulli’s principle and Venturi effect

Bernoulli’s principle states that as the speed of a fluid increases, the pressure and temperature decrease. The venturi effect is the demonstration of this principle in a confined pipe.
According to Bernoulli’s principle, the flow speed of a fluid is inversely proportional to its static pressure. This means that, when the velocity of the fluid increases, its pressure will decrease. The Venturi effect is a version of Bernoulli’s principle, but more specifically suited to the flow of fluids through a pipe.
When a fluid traveling through a pipe hits a constriction, it indicates the surface area has decreased at that point, resulting in a smaller opening. The ‘Principle of Continuity’ states that the rate at which mass enters and exits an isolated system remains constant, hence the fluid flow rate cannot, therefore, decrease. Therefore, in order to go the same distance in the same period of time and retain the same rate of flow, fluid molecules must flow through the restriction at a faster rate. As a result, the flow velocity increases.

In other words, there will be a pressure drop as the flow enters the confined zone. If the pressure decreases for an incompressible flow along a given streamline, the velocity must increase to maintain the RHS of Bernoulli’s principle constant. This explains why the Venturi effect causes an increase in flow rate. It should be evident from the fundamental flow rate solution in laminar flow that the pressure gradient increases in the confined region, so the flow rate should increase.

## How does the venturi effect work?

When a fluid traveling through a pipe hits a constriction, it indicates the surface area has decreased at that point, resulting in a smaller opening. The ‘Principle of Continuity’ states that the rate at which mass enters an isolated system and exits it remains constant, hence the fluid cannot flow at a lower rate than it does currently. Therefore, in order to maintain the same rate of flow, the fluid molecules must rush through the restriction more quickly in order to travel the same distance in the same amount of time. This causes the flow speed to rise. The formula for the kinetic energy of the fluid is:

KE = ( 1/2 ) × ρ × v2

Here, ρ is the fluid’s mass density, and v is its flow speed. When the fluid’s velocity increases at the constriction, so does its kinetic energy. However, according to the Law of ‘Energy Conservation,’ energy cannot be created or destroyed. This implies that total energy must remain constant. Thus, when the fluid’s kinetic energy grows, its pressure, which is nothing more than its energy density, reduces accordingly, so that the total quantity of energy remains constant and the Law of Conservation of Energy holds.

## Applications of venturi effect

### In carburetors

It is utilized in carburetors; in this case, the difference in inlet air pressure draws gasoline to the carburetor. When fuel is taken from the oil tank, it combines with air and generates a thin spray that allows for fine combustion.

### Pneumatic suction tube

Air can be sucked in instead of liquids from a reservoir as a carburetor does. This results in a negative pressure within the reservoir. Suction cups use this idea to produce a vacuum.

### Airplanes

The wings of airplanes are designed to increase the speed of the wind passing over them. A fast velocity, according to Bernoulli’s principle, results in a low-pressure area. The air beneath the wings rushes upwards to fill this vacuum, creating an upward lift and allowing flight. airplane, boat water speed, and in certain industrial applications to monitor liquid, air, and gas flow velocities.

### Pitot tube

A Pitot tube is a flow measurement device that uses the Venturi effect to determine fluid flow velocity. It is commonly used to calculate an aircraft’s airspeed.

### Spraying Nozzles

Pressing the nozzle of a paint gun causes pressured air to be expelled via a constriction. A paint container is linked to this chamber, and the consequent low pressure forces the paint out with the air. When you press the nozzle on a perfume bottle, compressed air is released at great speed out of a restricted aperture. As a result of the low pressure that has been generated in this area, which is connected to the perfume chamber, the liquid molecules are driven out of the area after mixing with the air.

### A draft causes doors to slam

The Venturi effect is also responsible for door slamming due to a draft. The door gap is a narrow cross-section through which air flows swiftly. The pressure in the space between the door and the frame decreases. The air normally flows significantly slower around the door leaf. The door slams with enormous power because the pressure on the door leaf is higher than the pressure in the gap, even though the air stream is flowing in the door’s opening direction.

### The Venturi Meter

A Venturi meter is used to measure the flow rate of fluids. It consists of a basic tube with a constriction coupled to a manometer. A manometer is a U-shaped glass tube that comprises a liquid such as water or mercury. Each manometer arm is attached to one side of the tube. The Venturi meter is put into a moving liquid or gas to measure the speed. The pressure of this fluid lowers as it approaches the narrow section of the tube. Because of the pressure drop, the liquid in the manometer rises in the arm attached to the constriction. The level in the opposite arm falls. The variation in the levels aids in determining the fluid’s flow rate.

### A wine bottle decanter

Wine scents emerge best when oxygen is supplied to the wine. This is accomplished by placing a decanter on the wine bottle before pouring. The spout’s cross-section narrows, causing the outflow velocity to increase. The resulting negative pressure sucks in air from the surrounding environment and incorporates it into the wine as it is poured from the bottle.

### Aquarium Aerators

For fish to survive, aquariums must have adequate amounts of dissolved oxygen, which is maintained by aerating pumps. They operate by directing water via a pipe with a constriction, or restricted opening. This pipe is connected to an open-air hose. Water creates a momentary vacuum when it travels through the constriction. This takes air from the hose into the pipe and delivers it to the tank.

### Gas stoves

Gas stoves use an inspirator, a Venturi tube with a constriction, and air input. Pressurized gas enters the tube and flows through the tiny hole when the gas supply is turned on. A vacuum is produced at this constriction due to an increase in the speed of the gas. Air flows in from the inlet and combines with the gas provided to the burner to fill the vacuum.

### In oxygen therapy

The venturi mask, also known as an air-entrainment mask, is medical equipment that allows patients on controlled oxygen therapy to get a known oxygen concentration.

## References

1. https://byjus.com/physics/venturi-tube/.