Thermal Expansion

Materials which contract with increasing temperature are rare; this effect is limited in size, and only occurs within limited temperature ranges. The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature.

Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:

Metal framed windows need rubber spacers

Rubber tires

Heat transfer

Heat transfer is the transition of thermal energy from a hotter mass to a cooler mass. When an object is at a different temperature from its surroundings or another object, transfer of thermal energy, also known as heat flow, or heat exchange, occurs in such a way that the body and the surroundings reach thermal equilibrium; this means that they are at the same temperature.

Conduction

Conduction is the transfer of heat by direct contact of particles of matter. The transfer of energy could be primarily by elastic impact as in fluids or by free electron diffusion as predominant in metals or phonon vibration as predominant in insulators. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is greater in solids, where a network of relatively fixed spacial relationships between atoms helps to transfer energy between them by vibration.

Convection

Convection is the transfer of thermal energy by the movement of molecules from one part of the material to another. As the fluid motion increases, so does the convective heat transfer. The presence of bulk motion of the fluid enhances the heat transfer between the solid surface and the fluid.

Radiation

Radiation is the transfer of heat energy through empty space. All objects with a temperature above absolute zero radiate energy at a rate equal to their emissivity multiplied by the rate at which energy would radiate from them if they were a black body.