1、 1 外文翻译 学 院： 专 业： 建筑环境与设备工程 班 级： 学 号： 姓 名： 指导教师： 2 5 Radiation Transmission through Glazing: Absorbed Radiation The transmission, reflection, and absorption of solar radiation by the various parts of a solar collector are important in determining collector performance. The transmittance, reflectance
2、, and absorptance are functions of the incoming radiation, thickness, refractive index, and extinction coefficient of the material. Generally, the refractive index n and the extinction coefficient K of the cover material are functions of the wavelength of the radiation. However, in this chapter, all
3、 properties initially will be assumed to be independent of wavelength. This is an excellent assumption for glass, the most common solar collector cover material. Some cover materials have significant optical property variations with wavelength, and spectral dependence of properties is considered in
4、Section 5.7. Incident solar radiation is unpolarized (or only slightly polarized). However, polarization considerations are important as radiation becomes partially polarized as it passes through collector covers. The last sections of this chapter treat the absorption of solar radiation by collector
5、s, collector-storage walls, and rooms on an hourly and on a monthly average basis. Reviews of important considerations of transmission of solar radiation have been presented by Dietz (1954, 1963) and by Siegel and Howell (2002). 5.1 REFLECTION OF RADIATION For smooth surfaces Fresnel has derived exp
6、ressions for the reflection of unpolarized radiation on passing from medium 1 with a refractive index 1n to medium 2 with refractive index 2n: 221221s i n ( )s i n ( )r (5.1.1) 3 2 212 21t a n ( )t a n ( )rP (5.1.2） 2rirrIrI P (5.1.3) where 1 and 2 are the angles of incidence and refraction, as show
7、n in Figure 5.1.1. Equation 5.1.1 represents the perpendicular component of unpolarized radiation r, and Equation 5.1.2 represents the parallel component of unpolarized radiation rP. (Parallel and perpendicular refer to the plane defined by the incident beam and the surface normal.) Equation 5.1.3 t
8、hen gives the reflection of unpolarized radiation as the average of the two components. The angles 1 and 2 are related to the indices of refraction by Snells law, Figure 5.1.1 Angles of incidence and refraction in media with refractive indices n1 and n2. 1 1 2 2s i n s i nnn (5.1.4) Thus if the angl
9、e of incidence and refractive indices are known, Equations 5.1.1 through 5.1.4 are sufficient to calculate the reflectance of the single interface For radiation at normal incidence both 1 and 2 are zero, and Equations 5.1.3 and 5.1.4 can be combined to yield 21212( 0 ) riI n nrI n n （ 5.1.5） If one medium is air (i.e., a refractive index of nearly unity), Equation 5.1.5 becomes 21( 0 )1nrn (5.1.6) Example 5.1.1 Calculate the reflectance of one surface of glass at normal incidence and at 60. The average index of refraction of glass for the solar spectrum is 1.526.
