Effects of thickeners on thermophysical properties of Alum as phase change material for energy storage

Abstract The main objective of this research is to characterize, via experimental analysis, the effects of thickeners on thermophysical properties of Alum (KAl[SO 4 ] 2 ·12H 2 O) as phase change material (PCM) for energy storage. Six thickeners, including sodium carboxymethyl cellulose (CMC‐Na), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol, xanthan gum (XG) and methylcellulose (MC), are added in Alum. Then the thermophysical properties and the cycle stability are tested and analyzed by step cooling experiment, differential scanning calorimeter, hot disk, scanning electron microscopy, high‐low temperature alternating test chamber, X‐ray diffraction (XRD), and Fourier transform infrared spectrometer (FT‐IR). The results showed that the adding of 2 wt% CMC‐Na, 1 wt% PAAS, 2 wt% PAM, 5 wt% XG, and 1 wt% MC to Alum can effectively reduce the subcooling of Alum while still maintaining the latent heat at a high level. After stability test with 60 melting‐solidification cycles, the results indicate that Alum with 1 wt% MC has the best thermal cycle stability and has the highest latent heat (230 J/g). The latent heat is only 8.1% lower than that of pure Alum after 1 cycle, and 11.1% higher than that of pure Alum after 60 cycles. The XRD, FT‐IR, and thermogravimetry results show that it has good chemical and thermal stability.