Experimental Measurement of Corrosion Involving Inorganics (Salt Hydrates) Phase Change Materials (PCM) for Thermal Energy Storage (TES) Applications

Abstract

Phase Change Materials (PCMs) have gained popularity for their high energy storage densities, which makes them suitable for various applications including, as heat transfer fluids (HTF) for waste heat management and supplementary thermal energy storage (TES) systems for dry cooling enhancement. PCMs are also used for Latent Heat Thermal Energy Storage Systems (LHTESS). PCMs can be classified as organic (i.e. Paraffin, and Fatty acids) and inorganic (i.e. Salt hydrates). For a given volume, salt hydrates tend to have larger storage capacity due to their higher densities compared to that of organic PCMs. However, corrosive nature of salt hydrates towards various metals and alloys renders a challenge for their engineering applications. Corrosion is further enhanced on addition of nucleating agents to the PCMs. Additives can affect the operational performance and efficacy of PCMs. The effect of additives on the corrosivity of these PCMs are currently lacking in the contemporary literature. Hence, in this study the effect of nucleating agents (additives) on the rate of corrosion is explored for applications in LHTESS. In this study, various PCMs in liquid phase (with or without nucleating additives) are exposed to a variety of test coupons. The test coupons are made from stainless steel (SS347) and aluminum (AL 1000 Series). The corrosion tests were performed in sealed glass test tubes. The PCM samples utilized in the corrosion tests are lithium nitrate trihydrate, zinc nitrate hexahydrate, and calcium chloride hexahydrate. The glass tubes were fully submerged in 45°C water bath for 6 ~ 18 weeks. The mass loss of the test coupons were measured at 6 week intervals. The results obtained in this study were compared to the literature data and the efficacy of the various PCM samples for TES applications were explored. This study helped in the selection of appropriate platforms for the ARPA-E ARID program based on their material compatibility. The study showed that aluminum (Al 1000 series) and stainless steel (SS 347) metals are corrosion resistance to lithium nitrate trihydrate. Whereas only stainless steel (SS 347) is corrosion resistance to zinc nitrate hexahydrate and calcium chloride hexahydrate. Aluminum (AL 1000 series) metals are not recommended for usage with zinc nitrate hexahydrate and calcium chloride hexahydrate due to their high corrosion rate of 71 and 127 mg/cm2.yr.