Construction and Working ‘It is a device used to measure the speed and flow rate or discharge of fluid through a pipe.’ Venturimeter is work on Bernoulli’s equation. Its basic principle also depend on Bernoulli’s equation and continuity equation.

Venturimeter : This device is used to measure the rate of flow (or say flow speed) of the incompressible fluid flowing through a pipe. It works on the principle of Bernoulli’s theorem. It consists of two wider tubes A and A’ (with cross sectional area A) connected by a narrow tube B (with cross sectional area a).

A manometer in the form of U-tube is also attached between the wide and narrow tubes. The manometer contains a liquid of density ‘ρ m ‘. Let P 1 be the pressure of the fluid at the wider region of the tube A. Let us assume that the fluid of density ‘ρ’ flows from the pipe with speed ‘v 1 ‘ and into the narrow region, its speed increases to ‘v 2 ‘.

According to the Bernoulli’s equation, this increase in speed is accompanied by a decrease in the fluid pressure P 2 at the narrow region of the tube B. Therefore, the pressure difference between the tubes A and B‘ is noted by measuring the height difference (∆P = P 1 – P 2 ) between the surfaces of the manometer liquid. From the above equation, the pressure difference The volume of the liquid flowing out per second is

Contents

#### What is a venturimeter used for?

Main parts of Venturimeter – The main parts of a venturimeter are:

- A short converging part: It is that portion of the venturi where the fluid gets converges.
- Throat: It is the portion that lies in between the converging and diverging part of the venturi. The cross section of the throat is much less than the cross section of the converging and diverging parts. As the fluid enters in the throat, its velocity increases and pressure decreases.
- Diverging part: It is the portion of the venturimeter (venturi) where the fluid gets diverges.

#### What is the function of Venturi?

A venturi is a device that can be used to measure the flow of fluid in a pipe. The fluid flow rate can also be increased by using a venturi. Venturimeter is a type of flowmeter that works on the principle of Bernoulli’s Equation.

### What is the central part of the venturimeter?

Construction of Venturimeter: –

As stated above, it consists of three parts, the part of the larynx and the deviation. These three parts are arranged in a systematic order. The first is an inlet section or converging section. This is the area where the cross-section emerges in a conical shape for contact with the throat region. In this section, the cross-section area decreases from beginning to end. This section is connected by an inlet pipe at one end and a cylindrical throat at the other end. The angle of convergence is typically 20–22 °. the other is a cylindrical larynx. This is the central part of the venturimeter. It is a cylindrical pipe in the ventimeter through which the fluid passes after converting to the convergence section. The throat usually has a diameter of the throat that is half the diameter of the pipe. The throat diameter remains the same through its length. The last one is turning the section. This is the end of the ventimeter. On one side, it is connected to the throat of the venturimeter, and on the other side is attached to the pipe. The divergent section has an angle of 5 to 15 degrees. The deviation angle is less than the convergence angle because the length of the deviation cone is larger than the convergence cone. The main reason for the small deviation angle is to avoid isolation of the flow from the walls.

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## How is the rate of flow calculated in a venturimeter?

Working – The venturimeter is used to measure the rate of flow of a fluid flowing through the pipes. Lets understand how it does this measurement step by step.

- Here we have considered two cross section, first at the inlet and the second one is at the throat. The difference in the pressure heads of these two sections is used to calculate the rate of flow through venturimeter.
- As the water enters at the inlet section i.e. in the converging part it converges and reaches to the throat.
- The throat has the uniform cross section area and least cross section area in the venturimeter. As the water enters in the throat its velocity gets increases and due to increase in the velocity the pressure drops to the minimum.
- Now there is a pressure difference of the fluid at the two sections. At the section 1(i.e. at the inlet) the pressure of the fluid is maximum and the velocity is minimum. And at the section 2 (at the throat) the velocity of the fluid is maximum and the pressure is minimum.
- The pressure difference at the two section can be seen in the manometer attached at both the section.
- This pressure difference is used to calculate the rate flow of a fluid flowing through a pipe.

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