Methods of Heat Transfer
Remember that heat is the presence of thermal energy or excited molecules. Cold, on the other hand is the absence of heat. When we touch something and feel that it is cool, it is because the heat in our hands and fingers is transferring towards the object and we feel the coolness of the object. Our bodies have heat because it is constantly working on a molecular level, and our fat content works as insulation, thereby storing heat and keeping us warm.
There are three methods of heat transfer. These methods are conduction, convection, and radiation. Conduction of heat occurs when the object experiences direct contact with the heat source. The atoms in the object begin to move and the object begins to heat up. When atoms move throughout the entire object, this object can conduct heat onto another object so long as it doesn't lose its contact with the heat source.
An example of this is what happens when a metal rod is heated with an open flame. The metal rod heats up. Without losing contact with the flame, if the metal rod touches a piece of cloth, the cloth will start to burn up due to the heat of the metal rod. The transfers of heat from the flame to the rod and from rod to the cloth are both examples of conduction.
Convection is the method of heat transfer that occurs when the object being heated physically moves and in doing so heats up. This can occur in liquids and gases, and not in solids. For example, when you put water in a kettle and heat it over the stove, the water begins to boil. Boiling water is an example of the physical movement caused by heat. Because the water is in motion, the molecules heat up. This example can be argued as an example of conduction as well since the water is touching the kettle which is touching the hot stove. If you are able to turn or circulate water really quickly without using a stove, you will notice that it will also be warmer than the temperature you began with.
Finally, radiation involves transferring heat in the form of waves through space. This can be explained by studying the relationship of the earth and the sun. The sun heats the earth by radiating light and heat through the space between the two celestial bodies. The sun never physically touches the earth, so it doesn't conduct heat, nor does it physically move the earth, so it doesn't convect heat (though it can convect heat to air on earth, but not without radiating first.) When you focus an infrared lamp or intense light on any object but never allow the objects to touch, you are demonstrating heat transfer in the form of radiation.
The three methods of heat transfer have been very useful to modern society. Conduction and convection help us cook our food, run machines, heat our swimming pools or water for our baths. Radiation has helped us heat our homes, and cure us or examine us from disease, such as the type of radiation used on malignant tumors or cancer.
Next Article: Conduction, Convection and Radiation
