Theoretical and experimental determination of chemical and physical properties of novel high thermal energy density molten salt systems for concentrating solar power (csp) storage
By using thermodynamic modeling, new eutectic multi-component salt systems have been developed. On the basis of the melting points, the novel systems were categorized into low melting point (LMP) systems and high melting point (HMP) systems. LMP can be used to serve as heat transfer fluid for solar parabolic trough system while the HMP can be used in solar tower or dish systems. Both LMP and HMP systems were synthesized and their melting points and heat capacities were determined using Differential Scanning Calorimetry (DSC). The experimentally determined melting points have excellent agreement with the predicted values. The densities for the selected systems were experimentally determined by using both standard densitometer method and Archimedes's principle method. In liquid state, the density values of both LMP and HMP systems decrease linearly as temperature increases. Thermal stabilities of novel systems were determined using TG-DTA. The upper limit temperatures of thermal stability were evaluated for LMP and most of values were found in the range between 673.15K and 723.15K. Compare to LMP systems, HMP salt mixtures show much higher upper limit temperatures, which enable them to be applied as heat transfer fluid for high temperature solar energy collection systems. Thermal conductivities in solid states of salt mixtures were also tested using simplified inverse method. For both LMP and HMP systems, the thermal conductivities decrease as function of temperature. Life cycle information such as the corrosion behaviors of various metallic samples in contact with molten salt systems was determined using both electrochemical method and isothermal dipping method. When dipped inside the LMP systems, protective and dense oxide scales formed on the sample surface prevent any further severe corrosion. For HMP systems, Ni-201 alloy has excellent resistance to high temperature corrosion and can be considered as the construction material for molten salt container. On the basis of density, heat capacity and the melting point, energy storage densities of novel systems were calculated and compared to the existing binary solar salt and HITEC salt. The larger thermal energy density values of current molten salts indicate the better energy storage capacity for solar power generation systems.