Venturimeter Principle, Construction and Working with Diagram

What is Venturimeter?

A venturimeter is a device used for measuring the rate of flow of a fluid flowing through a pipe.

Main parts of Veturimeter

The main parts of a venturimeter are:

Main parts of Veturimeter

  1. A short converging part: It is that portion of the venturi where the fluid gets converges.
  2. 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.
  3. Diverging part: It is the portion of the venturimeter (venturi) where the fluid gets diverges.

Principle of venturimeter

The working of venturimeter is based on the principle of Bernoulli’s equation.

Bernoulli’s Statement: it states that in a steady, ideal flow of an incompressible fluid, the total energy at any point of the fluid is constant. The total energy consists of pressure energy, kenetic energy and potential energy or datum energy.

Mathematically



Here all the energies are taken per unit weight of the fluid.

The Bernoulli’s equation for the fluid passing through the section 1 and 2 are given by



Construction

The construction of venturimeter is shown below:

It has three main parts

Venturimeter Principle, Construction and Working with Diagram

  1. Short converging part: It is a tapered portion whose radius decreases as we move forward.
  2. Throat: It is middle portion of the venturi. Here the velocity of the fluid increases and pressure decreases. It possesses the least cross section area.
  3. Diverging part: In this portion the fluid diverges.

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.

Expression for the rate of flow through Venturimeter

Considered a venturimeter is fitted to a horizontal pipe through which fluid ( water) is flowing as shown in the figure given below.

Venturimeter Principle, Construction and Working with Diagram


Let d1, p1, v1 & a1, are the diameter at the inlet, pressure at the inlet, velocity at the inlet and area  at the cross section 1. And d2, p2, v2 and a2 are the corresponding values at section 2.

Applying bernoulli’s equation at sections 1 and 2



As the pipe is horizontal, so z1 = z2
Therefore


(P1 – P2)/ρg is the difference of pressure heads at section 1 and 2 and it is equal to h. so



Substituting this value of h in equation (1), we get


Now applying continuity equation at section 1 and 2


Substituting this value of v1 in equation (2) and solving, we get


Discharge



Substituting value of v2 in above equation


Q is the theoretical discharge under ideal conditions. Actual discharge will be less than the theoretical discharge. The actual discharge is given by the formula



Where Cd is the coefficient of venturimeter and its value is less than 1.

Difference Between Rotary and Reciprocating Compressor

The difference between rotary and reciprocating compressor can be done on the basis of maximum delivery pressure, free discharge rate, speed of compressor, supply of air, size of compressor, balancing, lubrication system, cleanliness of delivered air, efficiency calculation, suitability, maintenance, initial cost, space requirement for installation, working fluid and cycle of operation.

Difference Between Rotary and Reciprocating Compressor

Difference between rotary and reciprocating compressor in tabular form


S.no
Basis
Rotary Air Compressor
Reciprocating Air Compressor
1.
Maximum delivery pressure
The maximum delivery pressure for rotary compressor is 10 bar only.
The maximum delivery pressure is as high as 1000 bar.
2.
Free air discharge rate
The maximum free air discharge rate is as high as 3000 m3/min.
The maximum free air discharge rate is about 300 m3/min.
3.
Speed of compressor
Speed is high.
Speed is low.
4.
Supply of air
The supply of air is continuous.
The supply of air is intermittent (i.e. not continuous).
5.
Size of compressor
Small for the given discharge.
Large for the same discharge.
6.
Balancing
No balancing problem
Balancing is a major problem
7.
Lubrication system
Simple lubrication system.
Complicated lubrication system.
8.
Cleanliness of delivered air
The delivered air is more clean because if does not come in contact with the lubricating oil.
The delivered air is less clean because it comes in contact with the lubricating oil.
9
Efficiency calculation
Isentropic efficiency is used for all sorts of calculation.
Isothermal efficiency is used for all sorts of calculation.
10
Suitability
They are suitable for large discharge of air at low pressure.
They are suitable for low discharge of air at high pressure.
11.
maintenance
Lower
Higher
12.
Initial cost
Lower
Higher
13.
Space requirement for installation
Less space is required.
More space is required.
14.
Working fluid
Air or some other gases.
Pressurised steam.
15.
Cycle of operation
Executes one step of Rankine cycle.
Executes whole Brayton cycle.

This is all about the difference between rotary and reciprocating compressor. If you find anything missing or incorrect than let me know through it by your comments.