Modes of Heat Transfer

The three basic modes of heat transfer are: - 

• Conduction

• Convection

• Radiation

Conduction: -

Heat conduction is a process in which heat energy is transferred from the hotter body to the colder part in a body without involving any actual movement of the molecules in the body. Heat transfer takes place from one surface to another surface because of the vibratory motion of the molecules. Heat transfer through the process of conduction occurs in substances which the surfaces in direct contact with each other. It generally takes place in solids.

For example: When frying vegetables in a pan. Heat transfer takes place from flame to the pan and then to the vegetables.

Based on the conductivity of heat, substances can be classified as conductors and insulators. Substances which conduct heat easily are known as conductors and those that do not conduct heat are known as insulators.

Convection: -

In this process, heat is transferred in the liquid or gases from a region of higher temperature to a region of lower temperature. Convection heat transfer occurs partly due to the actual movement of molecules or due to the mass transfer.

For example: Heating of milk in a pan. In this, Heat is transferred to milk with a medium of pan. There is no direct contact with the heat source.  

Radiation: -

It is the process in which heat is transferred from one body to another body without involving the molecules or the medium. Radiation heat transfer does not depend on the medium.

For example: In a microwave the substances are heated directly without any heating medium. Objects exposed to sunlight affect heat by radiation.

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