The transfer of heat from a region of higher temperature to a region of lower temperature occurs by three basic mechanisms:

• Conduction
• Convection
• Radiation

Heat Transfer Mechanisms

Conduction

In a solid, a liquid, or a gas is the movement of heat through a material by the transfer of kinetic energy between atoms or molecules.

The transfer of energy from the more energetic particles of a substance to the adjacent, less energetic one as a result of interactions between the particles.

Convection

In a gas or a liquid is the bulk movement of fluid caused by the tendency for hot areas to rise due to their lower density.

The mode of heat transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion.

Radiation

The dissemination of electromagnetic energy from a source. This does not require any intervening medium and occurs most efficiently through a vacuum.

The energy emitted by matter in the form of electromagnetic waves as a result of the changes in the electronic configurations of the atoms or molecules.

Thermal Conductivity

A physical property which describes its ability to transfer heat

Driving Force

The basic requirement for the heat transfer is the presence of a temperature difference.
No net heat transfer between two mediums that are at the same temperature.
The temperature difference is the driving force for heat transfer, just as the voltage different is the driving force for electric current flow and pressure difference is the driving force for fluid flow.

Temperature Gradient

Heat transfer occurs in the direction of hotter regions to colder regions.
If there is a temperature gradient, the heat transfer will act to destroy the gradient.
The shape of the temperature gradient is defined by the conditions (hot and cold face temperatures, thermal conductivity of barrier, heat capacity and thickness of material etc.).

Some Application Areas of Heat Transfer

• Car Radiators
• Power Plants
• Refrigeration Systems
• The Human Body
• Circuit Boards
• Air Conditioning
• Heat Pump
• Solar Collectors