Storage of Water in Inorganic Salt Hydrates and the Implications to Latent Heat in Phase Changes

ZHAN Jia, QIN Shan†, GAO Jing

The Key Laboratory of Orogenic Belts and Crustal Evolution (MOE), School of Earth and Space Sciences, Peking University, Beijing 100871; † Corresponding author, E-mail: sqin@pku.edu.cn

Abstract The dehydration processes of three selected inorganic salt hydrates, CUSO4·5H2O, NA2HPO4·12H2O and NA2SO4·10H2O, were respectively investigated to obtain the influence of water on the latent heat. Simultaneous DSC (differential scanning calorimetry)-tg (thermogravimetry) combined with Raman spectroscopy were employed to monitored the dehydration processes and the structural variations. The result reveals that for those salt hydrates which dehydrate mainly crystal water at melting point, the role of water in the structure directly influences not merely the thermal effect but the latent heat. For most salt hydrates, the water content exhibits a negative correlation with the latent heat for per mole water. NA2HPO4·12H2O melts to a salt hydrate with fewer moles of water, whereas NA2SO4·10H2O melts to its anhydrous form. Previous studies claim that there exists a quantitative relationship between the latent heat of salt hydrate and the number of crystal water. However, the comparison of the dehydration processes of NA2HPO4·12H2O and NA2SO4·10H2O indicates that whether this conclusion is generally applicable needs further study. Key words inorganic salt hydrate; crystal structure; latent heat

热能的储存分为显热储能和潜热储能。显热储能是利用材料所固有的热容进行的, 潜热储能则利用材料在相变时吸热或放热来实现能量的储存或释放[1–2]。这种材料在相变过程中可以保持恒温, 储

热密度大, 易于设计, 使用方便, 因此在太阳能热利用、废热余热回收、电力“移峰填谷”、热管理系统及建筑节能等领域有着广泛的应用前景[3–4]。作为相变材料的一个种类, 无机水合盐价格便宜, 储