先进材料疑固实验室 Heat transfer Laboratory of Advanced Materials Solidification Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. The characteristics of thermal radiation depend on various properties of the surface it is emanating from,including its temperature,its spectral absorptivity and spectral emissive power,as expressed by Kirchhoff's law.[3] The radiation is not monochromatic,i.e.,it does not consist of just a single frequency,but comprises a continuous dispersion of photon energies,its characteristic spectrum. If the radiating body and its surface are in thermodynamic equilibrium and the surface has perfect absorptivity at all wavelengths,it is characterized as a black body. A black body is also a perfect emitter.The radiation of such perfect emitters is called black-body radiation.The ratio of any body's emission relative to that of a black body is the body's emissivity,so that a black body has an emissivity of unity. 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITYHeat transfer Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. • The characteristics of thermal radiation depend on various properties of the surface it is emanating from, including its temperature, its spectral absorptivity and spectral emissive power, as expressed by Kirchhoff's law.[3] • The radiation is not monochromatic, i.e., it does not consist of just a single frequency, but comprises a continuous dispersion of photon energies, its characteristic spectrum. • If the radiating body and its surface are in thermodynamic equilibrium and the surface has perfect absorptivity at all wavelengths, it is characterized as a black body. • A black body is also a perfect emitter. The radiation of such perfect emitters is called black-body radiation. The ratio of any body's emission relative to that of a black body is the body's emissivity, so that a black body has an emissivity of unity