Thermal and Transport Properties of NaCl–KCl–ZnCl2 Eutectic Salts for New Generation High-Temperature Heat-Transfer Fluids

Abstract

Three eutectic salts from a system of halide salts NaCl–KCl–ZnCl2 were chosen for detailed study of thermal and transport properties with the objective of developing a next generation high-temperature heat-transfer fluid (HTF) for concentrated solar thermal power (CSP) technology. The acceptable range of the working temperatures for the HTF is from below 250 °C to at least 800 °C. The tested properties are presented here for the three candidate eutectic salts, including melting point, heat of fusion, heat capacity, vapor pressure, viscosity, density, and thermal conductivity. Data-fitted equations are provided for all the measured properties for convenience in engineering application. It is concluded that the three eutectic salts can satisfy the needs for a high-temperature HTF and thus are recommended as a new generation high-temperature HTF.

Experimental Test of Properties of KCl–MgCl2 Eutectic Molten Salt for Heat Transfer and Thermal Storage Fluid in Concentrated Solar Power Systems

“…An in-house developed density meter based on the Archimedean law was employed to conduct the experimental test for the density of MgCl 2 -KCl eutectic molten salt. The calibration of this device was completed in previous work [15]. The density of pure NaCl and KCl were measured using this system at 1200 C, and the difference is less than 1% when compared to data published in literature.…”

“…The studies about molten salts for many years have found that mixing different salts to form a eutectic system is a viable approach to lower the melting point and hold the high boiling temperature in the meantime. For example, eutectic nitrate molten salts were employed as HTF which could operate at temperatures as high as 550 C [15].…”

“…In order to achieve the target of a temperature as high as 800 C for a fluid being able to serve as HTF and thermal storage material in advanced CSP technologies bearing supercritical CO 2 power cycles, a system of chloride salts have been examined and recommended [15,16] due to their favorable thermal and transport properties, chemical stability at high temperatures, relatively low cost, and good availability from natural resources. A comprehensive literature survey has been reported in the authors' previous papers [15][16][17]. It has been found that MgCl 2 and KCl are two chloride salts candidates with high boiling point (1420 C and 1412 C, respectively), and can be available from mining or from the products of seawater desalination.…”

Advanced Materials for High‐Temperature Thermal Transport

“…Room to intermediate temperature TES has yet to identify an ideal system with both high gravimetric and volumetric energy densities . The state‐of‐the‐art large‐scale TES is based on molten salts, mostly solar salts (60 wt% NaNO 3 –40 wt% KNO 3 mixture) that have the stable liquid phase within the temperature window of 228 to 650 °C . Development of future TES systems with higher hot‐side temperature requires the solutions to a host of material issues, including suitable TES media (e.g., eutectic halide molten salts, liquid metals, and thermochemical reactions), as well as chemically stable and thermally insulating containment materials that interact with them …”

Solar Thermal‐Driven Desalination Pursuing Products of Pure Water and Salts and Leaving Minimum Impact to Environment

“…For example, the recent technology development on solar [31,[36][37][38] recently developed a chloride salt mixture (NaCl 7.5 wt%-KCl 23.9 wt%-ZnCl 2 68.6 wt%), its melting temperature is about 850 C, while its viscosity is only 0.325 Pa s at 300 C. The cost of this ternary chloride salt mixture is expected to be below 1 $/kg.…”