Exothermic Characteristics of Inorganic Phase Change Materials Suitable for Greenhouse Applications

In order to explore exothermic characteristics of four inorganic phase change materials of CaCl2·6H2O，Na2CO3·10H2O，Na2SO4·10H2O and Na2HPO4·12H2O under different environmental conditions，the experimental conditions were set between cold water and air.The phase change temperature and supercooling degree of four phase change materials under different media and temperature conditions were tested in 5，10 and 15 ℃ temperature solidification.Experimental results showed that phase change temperature of CaCl2·6H2O was about 30 ℃，it could not condense and release heat at 15 ℃；the phase transition temperature of Na2CO3·10H2O is about 31 ℃，the heat release of Na2SO4·10H2O was unstable，the latent heat of phase transition was small，and the secondary heat release phenomenon was obvious at 5 ℃；the phase transition temperature of Na2HPO4·12H2O was about 33 ℃.Supercooling degree of phase change materials in air environment was lower than that in cold water environment by comparing supercooling degree under different environmental conditions.With the increase of temperature，the supercooling degree of CaCl2·6H2O decreased gradually，while that of Na2CO3·10H2O increased gradually.The supercooling degree of Na2SO4·10H2O and Na2HPO4·12H2O had no obvious change.The degree of supercooling was related to thermal conductivity of heat transfer medium in cooling environment.The stronger the thermal conductivity （the thermal conductivity of water was stronger than that of air），the shorter the continuous heat release time in the phase change solidification process.