(83g) Thermal Conductivity of High Temperature Molten Salts for Concentrated Solar Power Applications

High temperature heat transfer fluids can play an important role in increasing the efficiency of solar thermal systems. Being able to operate at higher tempetaures than existing limit of traditional heat transfer fluids (synthetic oil at 400 ºC, and eutectic nitrate salts at 550 ºC), greately increases the efficiency of the system. However, identification and characterization of a suitable fluid with low melting point and high tempearature stability has been a challenge. It is imprative to have accurate measurement or correlation of the thermal conductivity (and other physical properties) of any newly developed fluid. The accurate assesment of these properties would enable the optimal design of other components of the solar plant such as piping system, and storage tanks. Several novel halide eutectic molten salt mixtures are proposed as future high temperature heat transfer fluids, to meet critical criteria that will advance the efficiency of concentrated solar power (CSP).

In this study, the thermal conductivity of low melting point (< 250 ºC) eutectics in three tertiary chlorinated compounds (1)NaCl, KCl, AlCl₃, (2) NaCl, KCl, ZnCl₂, and (3) NaCl, KCl, FeCl₃, are predicted based on the modified rough hard sphere theory. We have also measured the thermal conductivities of these systems at low temperature, and compared them with the predicted results from the model. All of the studied eutectic systems have melting points of less than 250 ºC, and low vapor pressure (less than 2 atm) at 1000 ºC. These novel salt mixtures are evaluated for their sutability as high tempearature heat transfer fluids in CSP technology.