Development, characterization and modification of mannitol-water based nanocomposite phase change materials for cold storage

Under the background of low carbon, phase change energy storage technology has been developed rapidly, which is widely used in solar energy utilization, industrial heat recovery, building temperature regulation, and cold chain logistics. In the fields of cold chain logistics, low-temperature phase change materials(PCMs) below 0 °C have great application space. However, the application of PCM in practice is still limited by high undercooling, low thermal conductivity, low cold storage efficiency and poor stability. In this paper, mannitol aqueous solution, which mannitol can reduce the undercooling degree, an organic-inorganic composite PCM, was used as the main energy storage. After adding MgCl₂ as cooling agent, a base solution of salt with phase change temperature of −6 °C and latent heat of 240.1 J/g was prepared. In order to improve the thermal conductivity and cold storage efficiency, nano-copper oxide (Nano CuO) and covalently modified hydroxylated multi-walled carbon nanotubes (MWCNT-OH) were added as thermal conductivity enhancers to prepare nano-composite phase change materials (NCPCMs). In order to obtain good dispersion effect in base solution, sodium dodecyl benzene sulfonate (SDBS), polyacrylamide (PAM) and Guar gum (GG) were used as dispersants. The effects of different dispersants on the dispersion of nanoparticles under phase transition behavior were investigated. The results showed that the anionic dispersant SDBS had poor dispersion effect in salt solution, while the polymer dispersant was better than PAM and GG. The thermal properties and cycle stability of NPCMs were also explored and the result show that the phase change system of mannitol/MgCl₂@MWCNT-OH/PAM had the best thermal performance, which has the thermal conductivity of 0.685 W/(m K), increased by 18.16 %, and the cold storage time was reduced by 57.3 %. Without supercooling, the NCPCM has high melting enthalpy, high thermal conductivity and good thermal stability, which has a broad development prospect in the field of cold chain.