Enhanced thermal conductivity and shape stabilized LiNO3-NaCl eutectic/exfoliated graphite composite for thermal energy storage applications

LiNO3 and NaCl salt mixtures are explored as phase change material (PCM) for thermal energy storage. We developed a process for synthesizing LiNO3 and NaCl eutectic mixture at room temperature and found that eutectic mixture consists of 88.8 wt% LiNO3 and 11.2 wt% NaCl salts. The latent heat and melting point of PCM are similar to 230 degrees C and 302 kJ kg(-1). Thermal conductivity of eutectic composition is measured with transient plane source (TPS) technique and value is 0.8 W m(-1) K-1. We used thermochemically exfoliated graphite (ExG) in 5, 10, 15, and 20 wt% ratio with the developed eutectic to prepare PCM-ExG composites to enhance thermal conductivity of pristine eutectic PCM. The maximum thermal conductivity of these PCM-ExG composite PCMs is similar to 13.8 W m(-1) K-1 for 20 wt% ExG and similar to 1400 kg m(-3) density, similar to 16.5 times of pristine eutectic PCM. We observed that PCM-ExG composite containing ExG >= 15 wt% retains liquid PCM inside the ExG pores, useful to reduce leakage problem of thermal energy storage vessel. The high thermal conductivity, high latent heat of fusion and suitable melting point of LiNO3-NaCl eutectic PCM-ExG composite PCM make it suitable for solar thermal energy storage and industrial waste heat recovery applications.