Charge Assessment for Nitrate-Based Salt as a Phase Change Material for a Medium-Temperature Latent Storage Tank

Abstract

The present study assesses the heat characteristic of the nitrate-salt mixture as a phase change material (PCM) for a medium-temperature latent storage system (LSS). Two binary and ternary mixtures are evaluated, which demonstrate different thermal behaviour. The highest melting and latent heat capacity is obtained by KNO3(0.4)/NaNO3(0.6) at 223.8 °C and 161.5 J/g. However, it has a higher supercooling degree with a partial phase transition between 217.6 °C and 251.5 °C, making it unfeasible for a medium-temperature LSS tank. The ternary mixture (TM) with NaNO2(0.4)/KNO2(0.53)/NaNO3(0.7) demonstrates a stable phase transition with minimum partial phase transition (22.1 °C) and suitable heat of fusion (98.1 J/g). Further evaluation through static thermal profiling demonstrates that the TM has a notable performance during solid-sensible charge with a charge level indicator (CLI) around 45.3 %–49.1 %. The TM can be charged up to 85.7 % until the end stage of the phase transition. It promotes a better storage capacity with suitable performance since the system can be charged effectively at a suitable temperature range (< 160 °C) for various applications. The micrograph observation indicates some dispersed particles and local agglomeration, which makes phase stabilization as an advantageous method to promote a stable phase change process. The TM can be considered a suitable PCM for a medium-temperature LSS tank that allows for a better solar thermal renewable system operation.