Water-graphene nanoplatelets based thermal energy storage material with nucleating and thickening agents: An investigation on thermal behavior during phase change

Application of the water-phase change material (PCM) in the cold thermal energy storage (CTES) units has been restricted due to the subcooling degree (SCD), instability, and lower thermal transport behavior. To sort out these issues, D-sorbitol (DS), Polymer polyacrylic acid sodium (PPAS) and graphene nanoplatelets (GNP) have been added as agents. Further, the influences of these agents on the thermal behavior of water-PCM during freezing/ melting in a spherical enclosure have been explored. At first, the excellent physical and chemical stability of the nanocomposite PCM (NCPCM) was confirmed through stability test and FTIR analysis. Seeding of DS and PPAS significantly reduced the SCD by 90 %, despite prolonged freezing and reduced thermal conductivity (TC). However, adding GNP maximized the TC by about 56 % and 15 % with 0.9 wt% in solid and liquid states; as a result, solidification and melting has been hastened by 18.6 % and 21.4 % respectively. Further, the reduced SCD was confirmed by identifying the droplet contact angle (DCA) of the water-PCMs and results showed a reduced DCA with increased wettability due to the PPAS and GNP addition. Overall, hastened freezing/melting process of the CTES system with the use of NCPCM can be helped to minimize the cost of energy by 5.6 % in a 2TR chiller unit for space cooling application.

Automated summary

The application of water-phase change material in cold thermal energy storage units has been improved by adding D-sorbitol, polymer polyacrylic acid sodium, and graphene nanoplatelets as agents. These agents enhance the thermal behavior of water-PCM, reducing subcooling degree, improving thermal conductivity, and accelerating freezing/melting processes, thus helping to minimize energy costs.