Preparation and thermal property enhancement of sodium acetate trihydrate-lithium chloride-potassium chloride expanded graphite composite phase change materials

Abstract

Phase change materials (PCMs) present promising solutions for enhancing energy efficiency in solar heat pump systems. In our study, we have innovatively developed a composite PCMs (CPCMs) by combining sodium acetate trihydrate (CH3COONa·3H2O, SAT), lithium chloride (LiCl), potassium chloride (KCl), and incorporating expanded graphite (EG). This addition of high thermal conductivity EG was aimed at bolstering the CPCM's thermal stability. Our findings reveal that SAT-LiCl-KCl/EG CPCMs, with 14 wt% EG, significantly enhances thermal energy storage performance while preserving the fundamental phase change characteristics. The resulting CPCMs demonstrates a phase transition temperature of 49.3 °C and a latent heat of 196.4 J/g, ideally suited to meet the demands of hot water heat pump systems operating in the 45–50 °C range. Notably, the thermal conductivity of this CPCMs, following the incorporation of 14 wt% EG, registers at 4.54 W/(m K), representing a remarkable 10.6-fold increase compared to the SAT-LiCl-KCl ternary eutectic salt. To ensure long-term stability, secondary encapsulation with a thermally conductive sealant was applied. Subsequent tests involved subjecting the CPCM to 3000 heating/cooling cycles, resulting in minimal deviations, with the phase transition temperature shifting by approximately 1 °C and a modest 6 % reduction in latent heat of phase transition. These outcomes underscore the robustness and reliability of our developed composite phase change materials.