What is a Boiler? Different Types of Boiler

In this article we will study about what is a boiler? Different types of boiler(steam).

The boilers are used in power plants for the generation of steam. They are crucial for the working of a power plant. They are mostly used in the power plants where steam turbines are used for the generation of electricity. The knowledge of boiler is very essential if you are a mechanical engineer.

What is a Boiler? Different Types of Boiler

What is a Boiler?

A boiler is a closed vessel which is used to convert the water into high pressure steam. The high pressure steam so generated is used to generate power.

Working Principle of a Boiler

Working Principle of a Boiler

The boiler works on the same principle as the water is heated in a closed vessel and due to heating, the water changes into steam. This steam steam possesses high pressure kinetic energy.

The boiler contains water. The water is heated to its boiling temperature by the use of heat from the furnace. Due to heating of water, it gets converted into high pressure steam. The steam generated is passed through the steam turbines. As the high pressure steam strikes the turbine, it rotates the turbine. A generator is attached to the turbine and the generator also starts to rotate with the turbine and produces electricity.

Different Types of Boiler

Boilers can be classified in different basis but here I am discussing the only important basis of boiler classification.

1. According to the Contents in the Tubes

According to the contents in the tubes, the boilers can be classified as fire tube boiler and water tube boiler.

(i) Fire Tube Boiler: In fire tube boiler the fire or hot gas are present inside the tubes and water surrounds these fire tubes. Since fire is inside the tubes and hence it is named as fire tube boiler.
The heat from the hot gases is conducted through the walls of the tube to the water.

  • The examples of the fire tube boiler are: simple vertical boiler, Cochran boiler, Lancashire boiler, Cornish boiler, Locomotive boiler, Scotch marine boiler and Velcon boiler.
(ii). Water Tube Boiler: In water tube boilers, the water is present inside the tubes and the fire or hot gases surrounds these water tubes.

  • The examples of water tube boilers are: La-Mont boiler, Benson boiler, Stirling boiler, Babcock and Wilcox boiler, Yarrow boiler and Loeffler boiler.

2. According to the Number of Tubes

According to the no of tubes, the boilers are classified as single tube boiler and multitubular boilers.

(i). Single Tube Boilers: The boilers which contain one fire tube or water tube are called as single tube boiler.

  • The examples of single tube boilers are Cornish boiler and simple vertical boiler.

(ii). Multitubular Boiler: The boilers which has two or more water tube or fire tubes are called multi tubular boilers.
  • Lancashire boiler, Locomotive boiler, Cochran boiler, Babcock and Wilcox boilers are multitubular boilers.

3. According to the Position of the Furnace

According to the position of the furnace, the steam boilers are classified as internally fired boilers and externally fired boilers.

(i). Internally Fired Boilers: The boilers in which the furnace is located inside the boiler shell are called internally fired boilers.
  • Among all the fire tube boilers, most of the boilers are internally fired boilers.

(ii). Externally Fired Boilers: In externally fired boilers, the furnace is located outside the boiler shell. In this the furnace is arranged underneath in brick work setting.
  • Water tube boilers are always externally fired boilers.

4. According to the Axis of the Shell

According to the axis of the shell, the boilers are classified as vertical boilers and horizontal boilers.

(i). Vertical Boilers: the in which the axis of the shell is vertical are called vertical boilers.
  • Examples of vertical boilers are: simple vertical boiler and Cochran boiler.

(ii). Horizontal Boilers: when the axis of the shell in a boiler is found horizontal than it is called as horizontal boiler.
  • Lancashire boiler, Babcock and Wilcox boiler and locomotive boilers are examples of horizontal boilers.

5. According to the Methods of Circulation of Water and Steam

According to the method of circulation of water and steam, the steam boilers are divided into natural circulation boilers and forced circulation boilers.

(i). Natural Circulation Boilers: In natural circulation boilers, the circulation of water takes place naturally by the convection currents that set ups during the heating of water.
  • In most of the boilers there is a natural circulation of water such as Lancashire boiler, Cochran boiler etc.

(ii). Forced Circulation Boilers: In this type of steam boilers, the water circulation takes place with the help of a centrifugal pump driven by some external power. Here the circulation is forced by some external agency.
  • Forced circulation is used in high pressure boilers such as La-Mont boiler, Loeffer boiler, Benson boiler etc.

6. According to the use

According to the use, the boilers are classified as stationary boilers and mobile boilers

(i). Stationary Boilers: These are the boilers which are stationary and cannot be moved from one place to another. Once they are installed, cannot be transported to other destination.
  • These boilers are used in power plants and in industrial process works.

(ii). Mobile Boilers: these are the steam boilers which can be moved from one place to another.
  • Locomotive and marine boilers are mobile boilers.

In this article we have studied about what is a boiler?, different types of boiler. If you find anything missing or incorrect than don’t forget to comment. If you find this article informative than like us on Facebook.

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.


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


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.


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

(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


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.