Radiation heat transfer absorption capacity

Theoretical research has proved that the radiation ability of blackbody is:

= (This formula is called Stefane-niels Bohr Zmann Law, where is absolute temperature; Is the radiation constant of the blackbody (or Stefan-Boltzmann constant), and its value is 5.669× 10 W/(mK). For the convenience of application, this formula can be rewritten as:

[152-0 1] is the radiation coefficient of black body, and [kg 1] is 5.669W/(mK). This formula shows that temperature has a great influence on thermal radiation. Thermal radiation at low temperature (such as in ordinary heat exchangers) can often be ignored; At high temperature (such as in a furnace), it becomes the main heat transfer mode.

The wavelength distribution law of radiation energy of real objects varies with the object and temperature. Let [kg 1][kg 1] of an actual object radiate arbitrary waves, and [152-0ru] of a blackbody radiate the same wavelength at the same temperature; If /[ 152-0ru]= constant, that is, the radiation ability of an object has nothing to do with the wavelength, then the object is called a gray body. Most engineering materials are close to the gray body in the wavelength range of thermal radiation. The radiation ability of the gray body can be expressed as:

[152-02] in which (

At the same temperature, the ratio of radiation ability between an object and a blackbody is equal to the ratio of their respective radiation coefficients, that is, =/=/. It is called blackness, which represents the relative radiation ability of an object. G.R. Kirchhoff found that the ratio of radiation capacity to absorption rate of any object is the same, which is always equal to the radiation capacity of an absolute blackbody at the same temperature, namely:

This formula is called Kirchhoff's law. It shows that the absorption rate and blackness of the object are equal in value, that is, the greater the radiation ability of the object, the greater the absorption ability.