Modes of Heat Transfer
The process heat transfer is defined as the exchange of thermal energy between two or more physical systems. The rate of heat transfer completely depends on the system temperature and the properties of the principal medium through which the heat is transferred. The three major modes of heat transfer are conduction, convection and radiation.
1) Conduction is the mode of heat transfer in which the macroscopic collisions of different particles and the movement of electrons within a body. The microscopically colliding objects, such as atoms, electrons and molecules, which transfer disorganized microscopic kinetic and potential energy. Conduction takes place in solids, liquids, gases and plasmas, means all phases of matter. The energy is conducted as heat between two bodies is the function of temperature gradient (Temperature difference) between two bodies. Thermal conduction also called diffusion. The property of heat is that transfer heat from a hotter body to colder body . When the two bodies reaches the thermal equilibrium, heat transfer becomes diminished.
2) Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion. It involves combined effects of conduction and fluid motion. The faster the fluid motion, the greater the convection heat transfers. If there is any absence of bulk fluid motion, heat transfer between adjacent fluid and solid surface is by pure conduction.
3) Radiation is the mode of heat transfer which transfers of energy by electromagnetic waves between surfaces with different temperature, separated by a medium that is at least partially transparent to the radiation. Radiation is especially important at high temperatures, during combustion process but can also have measurable effect at room temperatures.
The following figures illustrate the conduction, convection and radiation process.
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