Background

There are three types of heat transfer: conduction, convection, and radiation. Conduction involves the transfer of heat through a solid. Convection involves the energy exchange between a surface and a fluid. Radiation involves the transfer of heat from electromagnetic waves and does not require a transferring medium such as air.

Types of Heat Transfer

Picture Source: http://www.roasterproject.com/2010/01/heat-transfer-the-basics/

Heat flux equations for the three heat transfer types:

Picture Source: http://industrials-heater.com/industrial-heaters/heat-transfer-by-conduction.html

There are two different types of convection: natural and forced. Natural convection is caused by a difference in fluid density due to temperature (e.g. warm air rises as cool air falls). Forced convection is caused by an external force on the fluid over the surface. Radiation is heat transfer between two objects that are not in contact.