Thermal conductivity improvement of chloride molten salts for better high temperature thermal energy storage

PI: Alparslan Oztekin
Co-PI(s): Joshua Charles, Sudhakar Neti
University: Lehigh University

Renewable energy technologies have begun to replace fossil power plants, with one of the consequences being an increase in electric supply variability. This issue is not negligible since solar energy does not match load characteristics after sunset and, if ignored, will eventually limit solar energy deployment.

One method for dealing with electric supply variability is through thermal energy storage. Thermal energy storage (TES) typically utilizes molten salts to store energy at temperatures close to 900 K. Currently, nitrate/nitrite salts are the most common TES salts, but chloride salts are seen to be more important in the future, especially for supercritical CO2 power generation cycles. Chloride salts are lower in cost and have better chemical stability at high temperatures. On the other hand, chloride salts can be corrosive and have low thermal conductivities, which results in higher system-level costs, as additional heat transfer area is required when transporting energy into or out of the salt.

Through embedding of salts into graphite foam (GF), researchers have shown significant improvements in conductivity. Graphite foam is a highly porous, carbon-based material with a high thermal conductivity. By embedding the chloride salt into the porous structure of the foam, the foam serves as additional heat transfer surface area for the salt. This additional heat transfer surface area increases the effective conductivity, which could reduce overall system-level costs, making the salt much more desirable. As part of the proposed experimental work, samples of GF embedded with chloride salts will be tested for thermal storage potential by drop calorimetry. Drop calorimetry has been used extensively by the Lehigh University Energy Research Center and is a proven method for determining the thermal storage capacity of a material. This thermal analysis will be used to ensure that the salt continues to have good TES thermal properties despite being embedded into GF.