This short note aims to give the reader a global overview of the principle of heat flux with more details:
It describes the rate of heat energy that passes through a surface. Depending on its exact definition, its unit can be expressed as either W/m2 or W. Practically, it originates from a temperature differences in a given system. The induced heat always flows from the hot to the cold side. In order for this phenomenon to exist, it requires, not only a temperature difference, but also a medium through which it can flow.
As you have understood, this phenomenon is complexed, multidimensional and imply the combination of three distinctives mechanisms based on the medium or the set of media where the temperature gradient occurs. Indeed, heat can flow through solid materials (in which case it is called conduction), through gases and liquids (which is called convection) and through electromagnetic waves (which is called radiation).
In addition, heat flux depends on the temperature difference and the thermal transfer coefficient. The following equation defines heat flux with respect to the temperature difference and the thermal transfer coefficient: **HF = ∆T x HTC **with HF, the Heat Flux, in W/m2, ∆T, the temperature difference [K], and HTC, the heat transfer coefficient, in W/(m2K).
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