Optimal selection of thickeners for the phase change material of Na2S2O3·5H2O–CH3COONa·3H2O
In order to solve the phase separation problem of Na 2 S 2 O 3 ·5H2O–CH3COONa·3H 2 O PCM (phase change material), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), xanthan gum (XG), sodium polyacrylate (PAAS) and polyacrylamide (PAM) were selected as additives. The effects of different proportions of the above thickeners on the supercooling degree, phase separation, phase change temperature and latent heat of Na 2 S 2 O 3 ·5H2O–CH3COONa·3H 2 O system were studied by using the cooling curve and DSC, so as to screen the best thickener for eutectic PCM. The experimental results show that CMC, XG and PAAS can eliminate the phase separation of Na 2 S 2 O 3 ·5H2O–CH3COONa·3H 2 O. Among them, the optimal ratio of CMC, XG and PAAS is 3 mass%, 3 mass% and 1 mass%, respectively. From the perspective of heat storage performance, PAAS is the optimal thickener for Na 2 S 2 O 3 ·5H2O–CH3COONa·3H 2 O. The phase change temperature is 40.5 °C. The subcooling degree is about 14.7 °C, and the latent heat is about 221 J g −1 . The melting time is 15 min. Only PAAS can make Na 2 S 2 O 3 ·5H2O–CH3COONa·3H 2 O eutectic PCM completely exothermic at room temperature, which can not only play the role of thickener to eliminate phase separation, but also is a nucleating agent. After 100 melting-solidification cycles, the change rate of latent heat value was only 5%, and the change rate of phase transition temperature was less than 1%. Considering heat storage performance and cyclic stability, PAAS is the optimal thickener for Na 2 S 2 O 3 ·5H2O–CH3COONa·3H 2 O PCM.
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