Absorption technique

The process of absorption of energy in a gaseous medium is well-modeled by the expression

	(7.1)

Equation 7.1 is presented in the context of one dimensional radiative heat transfer. Here, is the intensity of radiation in the direction along the x-coordinate and suffixindicates dependence on wavelength. Suffix 0 refers to the value of intensity at , namely the initial intensity before radiation enters the region filled with the medium being studied. The parameter is called absorption coefficient; it is dependent on the chemical composition of the material being studied as well as wavelength. Equation 7.1 is called Beer's law. Equation 7.1 shows that the gas has a transmittivity equal to

Hence, it has an absorptivity that can be calculated as

Total material properties can be determined from the spectral values by suitable integration over the entire range of wavelength .