Preparation and performance of modified sodium acetate trihydrate composite phase change material for thermal energy storage
【Abstract】Phase separation and supercooling are common phenomenon of salt hydrates, which is a key problem affecting the thermal stability and thermal performance of phase change material. Sodium acetate trihydrate (SAT), as a low and medium temperature salt hydrate, is the main study object. Carboxyl methyl cellulose (CMC) and disodium hydrogen phosphate dodecahydrate (DHPD) were firstly used to modify SAT by melt blending method. A high-performance composite phase change material (PCM) was prepared by optimizing the ratio of the additives. The thermophysical properties and stability of different samples were tested by using differential scanning calorimetry (DSC) and a melting-freezing setup. The effects of the additives on phase change enthalpy, phase change temperature, supercooling and phase separation were analyzed. Finally, a high-density heat reservoir was built by using the modified PCM and a phase change thermal storage water system was set up. The thermal storage and release performances of the system under different working conditions were analyzed. The results showed that adding 0.5% CMC as the thickening agent and 2% DHPD as the nuclear agent could avoid phase separation and decrease supercooling degree. The phase change enthalpy and temperature range of modified SAT were 258 k J·kg−1 and 57 °C, respectively. The modified PCM had good cycling stability and its supercooling degree was smaller than 2 °C. In addition, the output water temperatures of the phase change thermal storage water system under different cooling conditions can be heated up to over 50 °C. The efficiency was higher than 90% and the exothermic power was as high as 10 kW. The exothermic power, released heat and thermal storage/release efficiency increased with the decrease in the inlet water temperature. The system had good storage and release performance and its energy storage density was 2.6 times as higher as traditional water tank.
【Keywords】 salt hydrate; sodium acetate trihydrate; composite phase change material for thermal energy storage; supercooling; thermal stability; thermal storage and release;
(Translated by WANG YX)
 ZHANG Y P, HU H P, KONG X D, et al. Phase Change Energy Storage: Theory and Application [M]. Hefei: University of Science and Technology of China Press, 1996 (in Chinese).
 FARID M M, KHUDHAIR A M, RAZACK S A K, et al. A review on phase change energy storage: materials and applications [J]. Energy Conversion & Management, 2004, 45 (9/10): 1597–1615.
 SHARMA S D, SAGARA K. Latent heat storage materials and systems: a review [J]. International Journal of Green Energy, 2005, 2 (1): 1–56.
 WANG Y, YANG R, ZHANG Y P, et al. Recent progress in shapestabilized phase change materials [J]. Energy Storage Science and Technology, 2013, 4: 362–368 (in Chinese).
 AGYENIM F, HEWITT N, EAMES P, et al. A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS) [J]. Renewable and Sustainable Energy Reviews, 2010, 14 (2): 615–628.
 PIELICHOWSKA K, PIELICHOWSKI K. Phase change materials for thermal energy storage [J]. Progress in Materials Science, 2014, 65 (10): 67–123.
 SU W, DARKWA J, KOKOGIANNAKIS G. Review of solid-liquid phase change materials and their encapsulation technologies [J]. Renewable and Sustainable Energy Reviews, 2015, 48: 373–391.
 SHAO J, DARKWA J, KOKOGIANNAKIS G. Review of phase change emulsions (PCMEs) and their applications in HVAC systems [J]. Energy and Buildings, 2015, 94: 200–217.
 SHUKLA A, BUDDHI D, SAWHNEY R L. Solar water heaters with phase change material thermal energy storage medium: a review [J]. Renewable and Sustainable Energy Review, 2009, 13 (8): 2119–2125.
 SHARMA R K, GANESAN P, TYAGI V V, et al. Developments in organic solid-liquid phase change materials and their applications in thermal energy storage [J]. Energy Conversion and Management, 2015, 95: 193–228.
 KENISARIN M, MAHKAMOV K. Salt hydrates as latent heat storage materials: thermophysical properties and costs [J]. Solar Energy Materials and Solar Cells, 2016, 145: 255–286.
 MENG L R, GUO L J, LI X Y, et al. Salt hydrate based phase change material for thermal energy storage—a review [J]. Energy Storage Science and Technology, 2017, 6 (4): 623–631 (in Chinese).
 YUAN K J, ZHANG Z G, FANG X M, et al. Research progress of inorganic hydrated salts and their phase change heat storage composites [J]. Chemical Industry and Engineering Progress, 2016, 35 (6): 1820–1826 (in Chinese).
 ZHANG R Y. Phase Change Material and Phase Change Energy Storage Technology [M]. Beijing: Science Press, 2009 (in Chinese).
 ZHANG X M, CAI L Y, SU Z J, et al. Effects of ultrasound on phase separation and crystallization of sodium acetate trihydrate [J]. CIESC Journal, 2010, 61 (1): 104–108 (in Chinese).
 DANNEMAND M, KONG W Q, FAN J H, et al. Laboratory test of a prototype heat storage module based on stable supercooling of sodium acetate trihydrate [J]. Energy Procedia, 2015, 70: 172–181.
 LANE G A. Phase change materials for energy storage nucleation to prevent subcooling [J]. Solar Energy Material and Solar Cells, 1991, 27: 135–160.
 FANG Y T, JIN C, LIANG X H, et al. Preparation and performance of sodium acetate trihydrate/formamide composite phase change material [J]. CIESC Journal, 2015, 66 (12): 5142–5148 (in Chinese).
 XU J X, KE X F. An investigation on phase change property of CH3COONa·3H2O as energy storage material [J]. Development and Application of Materials, 2007, 22 (6): 24–27 (in Chinese).
 MAO J, PENG G, LI J, et al. As election and optimization experimental study of additives to thermal energy storage material sodium acetate trihydrate [J]. Energy and Environment Technology, 2009, 1: 14–17.
 LUISA F C, MANUEL I, CRISTIAN S, et al. Experimentation with a water tank including a PCM module [J]. Solar Energy Materials & Solar Cells, 2006, 90: 1273–1282.
 ANICA T, KRISTIAN L, BERNARD F. Analysis of the influence of operating conditions and geometric parameters on heat transfer in water-paraffin shell-and-tube latent thermal energy storage unit [J]. Applied Thermal Engineering, 2006, 26: 1830–1839.
 HAMMICK D L, GOADBY H K, BOOTH H. CLXXV-Disodium hydrogen phosphate dodecahydrate [J]. Journal of the Chemical Society, Transactions, 1920, 117: 1589–1592.
 SIDGWICK N V. CCXXI—The solubilities of the alkali formates and acetates in water [J]. Journal of the Chemical Society, Transactions, 1922, 121: 1837–1843.
 SANDNES B, REKSTAD J. Supercooling salt hydrates: stored enthalpy as a function of temperature [J]. Solar Energy, 2006, 80 (5): 616–625.