Heat transfer/modes of heat transfer

Heat transfer:

• According to the 2^nd law of thermodynamics, heat always transfers from a higher medium to a lower medium.
• Heat transfer takes place between two different temperature objects.
• Heat transfer takes place from a hot body to a cold body until both bodies get an equal temperature.
• Its transfer depends on the phase of substance i.e it is either solid/liquid/gas.
• It is expressed in watt.

Conduction:

• In this mode of heat transfer, the heat transfers from one atom to its neighboring atom through the molecular level.
• It takes place in the case of solid.   

Example:

Let's say 4 boys are standing in a row. If we give a book to the 1^st boy and tell him to give this book to the 4^th boy. Then one method is 1^st boy will pass the book to 2^nd and 2^nd will pass the book to 3^rd and 3^rd will pass the book to 4^th without changing the position.

The same scenario is followed by heat.

When we apply heat to the pot, the molecule of the pot transfers heat to its neighboring molecule without changing the position as per the above example. By this process heat transfers to all molecules of the pot.

Convection:

• This mode of heat transfer occurs due to the transfer of energy through the bulk masses.
• It takes place between solid and fluid (Air/Gas or liquids).
• It takes place between the two fluids.

 Example:

Here 4 boys are standing in a row. If we give a book to the 1^st student and tell him to give this book to the 4^th boy. Then the second method is 1^st boy will pass the book to the 4^th boy by changing the position. 

Heat follows the same process.

When we apply the heat to the pot, the pot will get heat by the conduction process, but the particles of water transfer heat by changing the position means after heat lower particles go to the top and top particle comes to below and this process will continue until all the particles get an equal temperature. This process is known as the convection process.

Radiation:

• This mode of heat transfer occurs as quantum pockets of light energy. This is the mode by which we receive solar energy from the sun.
• It does not require any medium.
• Here heat transfer in the form of electromagnetic waves.

Example:

Here 4 boys are standing in a row. If we give a book to the 1^st student and tell him to give this book to the 4^th boy. Then the third method is 1st boy will pass by throwing the book to the 4^th boy without changing the position. similarly, it is for heat.

Waste energies come out from the stove without any medium is known as Radiation.