Conduction is the transfer of heat or electricity through a medium from one point to another. The word comes from the Latin conductio, which means “to lead”. It is the most fundamental mode of heat transfer and occurs in all phases of matter: solid, liquid, and gas. Heat can be conducted through a material by means of thermal conduction (also known as diffusiveheat flow), or it can be transmitted by means of electrical conduction. In solids, conduction takes place via phonon diffusion; that is, heat is transferred between atoms or molecules when they collide with one another. In liquids and gases, conduction takes place via molecule-molecule collisions.
Thermal conductivity is a measure of a material’s ability to conduct heat. It is generally expressed in units of watts per meter per Kelvin (W/m·K). The higher the thermal conductivity of a material, the more rapidly heat will be conducted through it. Electrical conductivity is a measure of a material’s ability to conduct electricity and is generally expressed in units of siemens per meter (S/m). The higher the electrical conductivity of a material, the more easily it will allow an electric current to flow through it.
Materials that are good thermalconductors have high lattice vibration frequencies and low atomic masses; that is, they are lightweight and have numerous small atoms that are able to vibrate quickly. Good electricalconductors have high electron mobility; that is, their electrons are free to move about within the materials’ crystal structures. Metals are generally good thermal and electricalconductors because they possess these properties. Non-metallic materials such as ceramics and polymers are poor thermalconductors because they have low lattice vibration frequencies and high atomic masses. However, there are some non-metallic materials – such as carbon nanotubes – that have been shown to be excellent thermalconductors due largely to their extremely small diameters which enable them to take advantageof quantum effects .
The three typesof heat transfer – radiation , convection ,and conduction – all play important rolesin determining how fast heat will spreadthrough a medium . Radiation involvesemitting energy in the form of electromagneticwaves ; these waves travel throughthe vacuum of space at the speedof light until they encounter an object ,at which point they either pass throughentirely ( ifthe objectis transparent ),or bounce off( ifit ‘s opaque ). Convectioninvolves moving heated fluidscontaining molecules with kinetic energy ;as these molecules come into contactwith cooler molecules ,they transfer someof their energyto them ,causingthe fluids towarm up . Conductioninvolves transferringenergybetween particlesby wayoftheir mutual collisions ;as mentioned earlier ,this processis facilitated by havinga large numberof small particleswhich canvibrate quickly .
All three forms oftansfer play important rolein many naturalphenomenaand technologicalapplications . For example ,conductionis responsiblefor heatingup food on agrill ; convectioncauses fluidsto circulate arounda room so thatthe temperatureis evenly distributed ;and radiationallows sunlightto reach Earth’s surfaceand warm it up .