In
the heat storage applications, Na2HPO4·12H2O phase change materials (PCM) show significant
defects including form instability, high supercooling degree and low
thermal conductivity. Aiming at these drawbacks, the Na2HPO4·12H2O-alumina/expanded vermiculite
(EVM) form-stable composite phase change materials (NEA fs-CPCMs)
with supercooling suppression and heat transfer enhancement were prepared.
The favorable wettability of NEA fs-CPCMs was beneficial to their
form-stabilization (encapsulation mass fractions above 59.7 wt %).
The supercooling degree of NE5.3 was reduced to 1.4 °C after
adding 5.3 wt % alumina as the nucleating agent (decreased by 90%).
The surface effects of EVM and alumina and high wettability of PCM-alumina
were responsible for the supercooling suppression of PCM. Large specific
surface area of EVM could provide nucleation sites for crystallization
of PCM. The surface electronegativity of alumina increased the affinity
ability and diffusion rate of ions, thus effectively increasing the
probability of nucleation. The heat transfer of NEA fs-CPCMs was significantly
enhanced by the alumina as the thermal conductivity enhancement filler.
The thermal conductivity of NE5.3 reached 0.418 W/(m K). Thermal energy
storage behavior analysis indicated that the NEA fs-CPCMs showed large
heat storage capacity (melting process: 97–151 J/g; solidification
process: 60–89 J/g). The thermal reliability of NEA fs-CPCMs
was effectively improved by coated paraffin.
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