Preparation and thermal conductivity enhancement of binary non-eutectic phase change materials based on alum-urea for solar heat storage system

Heat accumulators using latent heat storage are commonly used in solar energy storage systems. Potassium aluminum sulfate dodecahydrate (Alum) is an inexpensive phase change material , but the high phase change temperature limits its application in heat accumulator. To address this limitation is controlling the melting temperature of Alum. In this study, Alum-urea mixtures were first developed by adding 10 wt% urea. Modified phase change materials (MPCM) without phase separation and supercooling were developed by adding NiSO 4 ·6H 2 O and xanthan gum to the Alum-urea mixture. Composite phase change materials (CPCM) with high thermal conductivity were developed by loading MPCM in expanded graphite . The melting temperature of the Alum-urea mixture was 72.52 °C with 10 wt% urea content, which was 21.4% lower compared to the Alum. The MPCM still has a high phase change enthalpy (157.7 J·g −1 ) and ignorable subcooling degree (0.8 °C). The thermal conductivity of CPCM is increased by 16 times, and it has good photothermal conversion ability. The CPCM holds significant promise for applications in latent heat energy storage.