ABSTRACT
For many centuries, heat was interpreted as an invisible form of matter called caloric. This caloric view persisted until about 1840, when the British physicist James Joule showed that heat was not a material substance, but rather a form of energy. Heat is not a property; instead, it is a mechanism to transfer energy across the boundaries of a system. The fundamental modes of heat transfer are conduction, convection, and radiation. Conduction heat transfer occurs from one part of a body to another, or between bodies in contact, without any movement on a macroscopic level. On the other hand, convection occurs when heat is transferred between a solid surface and a fluid region, or between different fluid regions, due to bulk fluid movement. In the case of forced convection, external processes (such as pressureinduced forces) drive the fluid motion; these external effects may result from devices such as pumps, fans, or atmospheric winds. In free convection, buoyancy (rather than external forces) drives the fluid motion. Finally, radiative heat transfer results from the emission of electromagnetic waves (or photons, i.e., packets of energy) by all surfaces above absolute zero. These processes will be described in detail in individual chapters devoted to each mode of heat transfer.
