Prevention of supercooling and stabilization of inorganic salt hydrates as latent heat storage materials

Abstract

Abstract Various inorganic salt hydrates have been studied as a latent heat storage medium. A super-absorbent polymer (SAP) made from an acrylic acid copolymer is proposed as an effective thickener to prevent undesirable phase separation of the high hydrate inorganic salts (Na2SO4· 10H2O, Na2HPO4·12H2O, Na2CO3·10H2O). Most of these materials can be stabilize by the addition of 3 to 5 wt% SAP as a thickener. For the low hydrate inorganic salts (CH3COONa· 3H2O, Na2S2O3·5H2O), carboxymethyl cellulose (CMC) is found to be an effective thickener. Similarly, the phase separation of the low hydrate salts can be prevented by the addition of 2 to 4 wt% thickener. To overcome the supercooling of the thickened phase change materials, various potential nucleators have been evaluated. For the thickened Glauber's salt, borax reduces supercooling of the salt from 15 to 3–4°C. Three different powders of carbon (1.5–6.7 μm), copper (1.5–2.5 μm) and titanum oxide (2–200 μm) are found to reduce the supercooling of thickened Na2HPO4·12H2O. Also, the supercooling of thickened CH3COONa·3H2O is reduced from 20 to 2–3°C by adding 2 wt% potassium sulfate. New compositions for preventing supercooling and phase separation of PCMs are developed in the temperature range 30–60°C: Glauber's salt/SAP/borax (94/3/3 wt%, Tm = 35°C), Na2CO3·10H2/SAP/Sr(OH)2 (93/3/4 wt%, Tm = 32°C), Na2HPO4·12H2O (92.8/3.5/3.7 wt%, Tm = 35°C), Na2S2O3·5H2O/CMC/ SrSO4 (92/3/5 wt%, Tm = 48°C), CH3COONa·3H2O/CMC/K2SO4 (95/3/2 wt%, Tm = 58°C).