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The vibrational and rotational excited states of greenhouse gases that emit thermal infrared radiation are in LTE up to about 60 km. [7] Radiative transfer calculations show negligible change (0.2%) due to absorption and emission above about 50 km. Schwarzschild's equation therefore is appropriate for most problems involving thermal infrared in ...
In general, the heat transfer between surfaces is governed by temperature, surface emissivity properties and the geometry of the surfaces. The relation for heat transfer can be written as an integral equation with boundary conditions based upon surface conditions. Kernel functions can be useful in approximating and solving this integral equation.
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
Radiative transfer (also called radiation transport) is the physical phenomenon of energy transfer in the form of electromagnetic radiation. The propagation of radiation through a medium is affected by absorption, emission, and scattering processes. The equation of radiative transfer describes these interactions mathematically. Equations of ...
The heat transfer processes (or kinetics) are governed by the rates at which various related physical phenomena occur, such as (for example) the rate of particle collisions in classical mechanics. These various states and kinetics determine the heat transfer, i.e., the net rate of energy storage or transport.
In reality, however, the radiosity will have a specular component from the reflected radiation. So, the heat transfer between two surfaces relies on both the view factor and the angle of reflected radiation. It was also assumed that the surface is a gray body, that is to say its emissivity is independent of radiation frequency or wavelength.
Intensity of thermal radiation from the sun depends on view factor. In radiative heat transfer, a view factor, , is the proportion of the radiation which leaves surface that strikes surface . In a complex 'scene' there can be any number of different objects, which can be divided in turn into even more surfaces and surface segments.
Naturally, a good reflector must be a poor absorber. This is why, for example, lightweight emergency thermal blankets are based on reflective metallic coatings: they lose little heat by radiation. Kirchhoff's great insight was to recognize the universality and uniqueness of the function that describes the black body emissive power.