Quote: Heat can be moved in three ways: By conduction, where heat is transferred by physical contact; by radiation, where heat is transferred over a distance via electromagnetic waves; and by convection. Convection is simply a combination of conduction and physical movement, where the material in contact with the heat source is fluid. Where the fluid contacts the heat source, it absorbs energy through conduction and its density changes as it gains heat. Because fluids are able to move freely, this now warmer and less dense area of fluid rises and physically carries its new heat energy away from the heat source.
This article will review the basic principles behind heat transfer. It will consider examples of each and discuss ways of optimizing heat transfer efficiency and, hopefully, help you save energy and reduce costs. Endquote
Understanding the Mechanics of Heat Transfer | 2013-08-21 | Process Heating