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الجمعة، 27 سبتمبر 2019




Heat Transfer
It’s a thermal engineering branch that concerns with the transfer of heat between different systems according to the temperature difference. Heat transfer can be defined according to thermodynamics as the movement of heat from any physical system to the surroundings depending on the temperature difference between them.

Temperature gradient between systems is so important for the transfer of heat between these systems. There are three different methods of heat transfer which are known as conduction, convection and radiation. These three methods will be discussed briefly in the next section of this article. 

Heat Transfer Methods
Conduction_ It’s the transfer of heat between atoms and particles in the case of rapid vibration and in contact with each other at the same time. The vibration of adjacent atoms is the main cause of the transfer of heat by conduction. This method of heat transfer occurs between solids which are in thermal contact. A hand on a cup of cold water is the best example on the transfer of heat by radiation, in this case the heat will transfer from the hand to the cup.

Convection_ In this method the heat transfers from any place to another by fluids’ movement. This method of heat transfer occurs in liquids and gases as it requires mass transfer. Convection cooling which is known as Newton’s law of cooling which provides for: “The rate of heat loss of a body is proportional to the temperature difference between the body and its surroundings” but, this law will be applied in only linear cases of convection.

Radiation_ In this method the heat transfers through any medium or vacuum as photons in electromagnetic waves. Radiation doesn’t require any matter to propagate as it can propagate through vacuum. The heat which come from the sun is the best example of the transfer of heat by radiation.

Heat Transfer Applications
Heat transfer is applied widely in almost all fields. It has a wide range of applications in everyday life. Here are the most important applications of heat transfer:

ü It’s applied in climate engineering for the management of solar radiation in order to decrease greenhouse gases effect.
ü It’s used for evaporative cooling which required for the conversion of the sensible heat to latent heat and that leads to the evaporation of water by transferring the heat from air to water.
ü It’s used in laser cooling techniques such as Doppler cooling which required to achieve a very law temperature near to absolute zero.
ü It’s applied in magnetic cooling which is used for achieving temperature degrees below 0.3 Kelvins by using magnetocaloric effect.
ü Thermal insulators are designed depending on the principles of heat transfer. These insulators are used for resisting the transfer of heat through materials.
ü There are many devices are functioned according to heat transfer principles such as thermoelectric cooler, thermal diode and thermocouple.
ü Heat exchangers which are widely used in all industries is the most important application of heat transfer. These devices exchange the heat between two materials to achieve the required heat. They are used in many devices such as refrigerators, power generators, and air conditioners.  

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