MOLTEN SALT SPECTROSCOPY FOR QUANTIFICATION OF RADIATIVE ABSORPTION IN NOVEL METAL CHLORIDE-ENHANCED THERMAL STORAGE MEDIA

摘要

This study describes the development and characterization of novel high-temperature thermal storage media, based on inclusion of transition metal chlorides in the potassium-sodium chloride eutectic system, (K-Na)Cl (melting temperature of 657°C, latent heat of 278 J/g). At the melting temperature of (K-Na)Cl, infrared (IR) radiation can play a major role in the overall heat transfer process-90 percent of spectral blackbody radiation falls in the range of 2 to 13 μm. The authors propose inclusion of small amounts (less than 0.2 wt %) of IR-active transition metal chlorides to increase radiative absorption and thereby enhance heat transfer rates. A new IR reflectance apparatus was developed to allow for determination of the spectral absorption coefficient of the newly formulated PCMs in the molten state. The apparatus consisted of an alumina crucible coated at the bottom with a reflective (platinum) or absorptive (graphite) surface, a heated ceramic crucible-holder, and a combination of zinc sulfide (ZnS) and zinc selenide (ZnSe) windows for containment of the salt and allowance of inert purge gas flow. Using this apparatus, IR spectra were obtained for various transition metal chloride additives in (K-Na)Cl, and improved infrared activity and radiative transfer properties were quantified. Further, thermophysical properties relevant to thermal energy storage (i.e., melting temperature, latent heat) are measured for the pure and additive-enhanced thermal storage medium.