A theoretical approach on estimating temperature-dependent optical properties of two typical molten alkali chloride salts (KCl and NaCl)

Abstract

Due to high working temperature of molten salts, radiative heat transfer has great effects on the temperature field computation accuracy. Since few optical property data of alkali chlorides is available, making it difficult to take radiative heat transfer into consideration, hence hindering its further application. In this paper, a theoretical approach on estimating temperature-dependent optical property of molten salts is developed to get temperature effect involved into optical property computation. After this, temperature-dependent optical properties of KCl and NaCl are estimated as an example. Due to the similarity of K and Na, the optical properties of KCl and NaCl exhibit extremely similar patterns. In short-wavelength region, they all show very high absorption intensity. In long-wavelength region the refractive index nearly keeps unchanged along with wavelength, while the extinction coefficient subtly increases. When temperature increases, the variations of optical properties of KCl are much more obviously than that of NaCl, but the overall trends are consistent. In short-wavelength region, an increase in temperature could lead to a slight red shift of refractive index peak and a decrease of extinction coefficient peak value. In long-wavelength region, increasing temperature will make both refractive index and extinction coefficient decrease.