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The sources of heat energy for domestic and industrial purposes are mainly wood, charcoal, petrol, kerosene, etc. These substances are called fuels. A good fuel is one which is readily available. It is cheap. It burns easily in air at a moderate rate. It produces a large amount of heat. It does not leave behind any undersirable substances.
There is probably no fuel that could be considered as an ideal fuel. We should look for a fuel which fulfils most of the requirements for a particular use. Fuels differ in their cost. Some fuels are cheaper than others.
Fuels can be divided into three main categories
Solid fuels: Solid fuels left some ash or residue after combustion. The solid fuels are given below.
|S. No.||Solid Fuels|
|2||Cow dung cake|
Liquid fuels: Most of the liquid fuels in use are the hydrocarbons which exist in the liquid phase at room temperature. The liquid fuels are given below.
|S. No.||Liquid Fuels|
Gaseous fuels: Some of the gaseous fuels exist naturally at room temperature and some are made by the treatment of coal. The gaseous fuels are given below.
|S. No.||Gaseous Fuels|
Suppose you were asked to boil a given quantity of water using cow dung, coal and LPG as fuel. The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg). Calorific values of some fuels are given in Table.
|Cow dung cake||6000-8000|
The increasing fuel consumption has harmful effects on the environment.
For centuries, wood was used as domestic and industrial fuel. But now it has been replaced by coal and other fuels like LPG. In many rural parts of our country, people still use wood as a fuel because of its easy availability and low cost. However, burning of wood gives a lot of smoke which is very harmful for human beings. It causes respiratory problem. Also, trees provide us with useful substances which are lost when wood is used as fuel. Moreover cutting of trees leads to deforestation which is quite harmful to the environment.
Global warming is the rise in temperature of the atmosphere of the earth. This results, among other things, in the melting of polar glaciers, which leads to a rise in the sea level, causing floods in the coastal areas. Low lying coastal areas may even be permanently submerged under water.
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