Semitransparent material

The absorption, reflection, and transmission of incident radiation by a semitransparent material. 

Similar quantities can be defined for the transmissivity of semitransparent materials. For example, the spcciral hemispherical transmissivity of a medium can be expressed as... 

The complex subject of thermal radiation transfer has received much study in recent years and is covered in a number of texts. The following introductory treatment discusses the following topics emission of radiation, absorption by opaque solids, radiation between surfaces, radiation to and from semitransparent materials, and combined heat transfer by conduction-convection and radiation. 

The major problem in using a single wavelength radiation thermometer to measure the surface temperature is the unknown emissivity of the measured surface. The emissivity is the major parameter in the spectral radiance temperature equation (Eq. 16.28) for the temperature evaluation. Objects encountered for temperature measurements are often oxidized metal surfaces, molten metal, or even semitransparent materials. On these surfaces, the emissivity is usually affected by the surface temperature and the manufacturing process for these materials. 

FIGURE 18.4 Steady-state temperature distributions in the x and z directions for a circular, CW, Gaussian irradiation of a moving, semitransparent material [26],... 

Source-Load Coupling for Opaque and Semitransparent Materials. Because no materials exhibit true gray behavior, a primary issue in the design or operation of process hardware is radiative source-load coupling. The coupling efficiency may be estimated only if the spectral radiative properties of the source and load are known. 

Semitransparent Material. When the load is not opaque, radiative heat transfer occurs within the material in conjunction with conduction and/or advective transfer (if the load is moved with respect to a coordinate system). The thermal response of the load is, therefore, determined in part by volumetric radiation heat transfer, necessitating prediction or measurement of the relevant radiative properties. 

Semitransparent material Material partially transparent for thermal radiation in certain wavelength regions the results of its measurement concerning the radiative heat transfer are influenced by the surface emittance of the boundaries... 

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