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Modes of heat transfer


Posted Date: 08-Jan-2011  Last Updated:   Category: Education    
Author: Member Level: Gold    Points: 30


Heat usually transfers from one place to another place via conduction, convection and radiation. This tutorial discusses about each mode of heat transfer in detail. Conduction is the mode of heat transfer with no molecular movement between the hot and cold body. Convection is the mode where heat is transferred by real molecular motion. Radiation is another mode which does not require even a medium for its propagation. Let see what is more,



Modes of heat transfer



We learned that transfer of heat occurs in three ways. Namely conduction, convection and radiation. Conduction heat transfer is found to be common in solids. Conduction in liquids and gases are found to a lesser extent. Convection heat transfer is another mode which can be found in the case of heat transfer between solids and gases, solids and liquids and within the liquids and gases. Radiation heat transfer requires no medium for propagation of heat transfer and heat radiation can be treated as electromagnetic radiations.

1. Conduction


When two bodies are in physical contact having a temperature difference between them or when there is a temperature gradient between two parts of the same body. Then method of heat transfer between them occurs almost by conduction. In conduction the molecules of the body are not moving as they are moving in the case of convection. Conduction heat transfer is found to be common in solids and between solids. Conduction in liquids and gases are also found in nature but will become negligible when comparing with the conduction in solids, see conduction in liquids and gases. To know the mechanism of conduction heat transfer and associated laws and derivations, see mechanism of heat transfer by conduction.
conduction in solids

2. Convection


Transfer of heat in liquids or between a solid body and a liquid occurs by mode of convection. Convection can be broadly classified in to free or natural convection and forced convection. Forced convection happens when there is an external pump work and in free convection the driving force for the molecular motion is the natural flow of heated particle to upper level by replacing cold molecules.
convection boiling
To have a better understanding, consider the boiling of water in a pot on your stove. Transfer of heat from the hot pot to the water occurs almost by convection. Water at the bottom of the pot gets heated up and become less dense and will begin to rise by replacing the cold water molecules from the top. This process continues till thermal equilibrium attains after you switching of the stove. To know more about different types of convection and mechanism of convection see heat transfer by convection.

3. Radiation


The rich amount of energy of heat and light from the sun to the earth which is necessary to sustain the life of living things on earth occurs by radiation heat transfer. Heat radiation thought as electromagnetic radiations and it is not necessary to have a medium for radiation takes place. In the case sun heat is radiated through vacuum.
radiation

All bodies having temperature greater than zero Kelvin will emit and receive heat radiations. Hot bodies emit heat radiations more than they receive. Cold bodies receive radiations than they emit. To know advanced theories behind radiation heat transfer see mechanism of radiation heat transfer.


Next: mechanism of conduction heat transfer Previous: Heat transfer



Related: Heat transfer, fluid mechanics
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