Heat transfer ; is the physical thermal energy generated by the exchange of heat between two systems.The concepts of temperature and heat flow are the two basic principles of heat transfer. The amount of thermal energy present is determined by temperature, and heat flow represents the movement of thermal energy.
When examined at a microscopic level, the kinetic energy of molecules is directly related to thermal energy. As the temperature increases, the thermal agitation caused by the linear motion and vibration of the molecules increases. Thus, the regions where higher kinetic energy is formed transfer energy to points with lower kinetic energy.
Types of Heat Transfer
Heat transfer can be simply classified into three categories: conduction, convection, and radiation.
Conduction: Heat transfer by conduction occurs when molecules collide directly with each other. A higher kinetic energy field transfers energy to a lower kinetic energy field. The higher speed particles collide with the lower speed particles. However, the kinetic energy of the lower speed particles increases. Conduction is the most common method of heat transfer and occurs through physical contact. An example would be placing a metal object over a burning fire.
Convection:A type of energy transfer between a solid surface and an adjacent moving liquid or gas. It involves the combined effects of conduction and fluid motion. The faster the fluid motion, the greater the convective heat transfer. If bulk fluid motion is eliminated, heat transfer between a solid surface and an adjacent fluid is by pure conduction.
Radiation: It is the energy emitted from matter in the form of electromagnetic waves (or photons) as a result of changes in the electronic arrangements of atoms and molecules. Unlike conduction and convection, heat transfer by radiation does not require an intermediary medium. Heat transfer by radiation occurs at the speed of light and does not slow down in a vacuum. The heat that the Earth receives from the sun is a result of electromagnetic waves traveling in the space between the Earth and the Sun. It is related to thermal radiation, which is the type of radiation that objects emit due to their temperature. All objects emit thermal radiation at temperatures above absolute zero.
