In thermal physics,<unk>  is the passage of thermal energy from a hot to a colder body. When a physical body, e.g. an object or fluid, is at a different temperature than its surroundings or another body,<unk>  of thermal energy, also known as<unk> , or<unk>  exchange, occurs in such a way that the body and the surroundings reach thermal equilibrium.<unk>  always occurs from a hot body to a cold one, a result of the second law of thermodynamics. Where there is a temperature difference between objects in proximity,<unk>  between them can never be stopped; it can only be slowed down.
Classical<unk>  of thermal energy occurs only through conduction, convection, radiation or any combination of these.<unk>  associated with carriage of the<unk>  of phase change by a substance (such as steam which carries the<unk>  of boiling) can be fundamentally treated as a variation of convection<unk> . In  each case, the driving force for<unk>  is a difference of temperature.There are 3 types of<unk>  known as convection, conduction and radiation.<unk>  is of particular interest to engineers, who attempt to understand and control the flow of<unk>  through the use of thermal insulation,<unk>  exchangers, and other devices.<unk>  is typically taught as undergraduate and graduate subjects in chemical, electrical and mechanical engineering curricula.<unk>  — a<unk>  of thermal energy, (i.e., of energy and entropy) from hotter material to cooler material.<unk>  may change the internal energy of materials.
Internal energy — the internal vibrational energy that the molecules or electrons composing all materials contain (except at absolute zero)
Conduction —<unk>  of<unk>  by electron diffusion or phonon vibrations (see below)
Convection —<unk>  of<unk>  by conduction in a moving medium, such as a fluid (see below)
Radiation —<unk>  of<unk>  by electromagnetic radiation or, equivalently, by photons (see below).
Phase change —<unk>  of<unk>  by the potential energy associated with the<unk>  of phase change, such as boiling, condensation, or freezing.
1-D Application Using Thermal Circuits — application of<unk>  analysis using the concept of thermal circuits.
Heat transfer
Blood flow
Oxygenation
Thermoregulation
Photosynthesis
Flux 
Muscle contraction
Drug metabolism