三水醋酸钠相变储能复合材料改性制备及储/放热特性
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摘要
水合盐相变储热材料普遍存在的过冷和相分离现象是影响其热稳定性和热性能的关键问题。以中低温水合盐相变储热材料三水醋酸钠(SAT)为研究对象,采用熔融共混法将羧甲基纤维素(CMC)和十二水磷酸氢二钠(DHPD)作为添加剂对三水醋酸钠进行了改性研究,通过各成分的配比优化制备了高性能相变储热复合材料,利用DSC及熔融-凝固装置对改性材料进行了热物性和稳定性的测试,分析了不同质量分数的添加剂对相变储热复合材料的相变焓、相变温度、过冷度及相分离现象的影响;在此基础上采用改性的SAT相变储热复合材料构建了高密度储热器并搭建了相变储能热水实验系统,研究了不同运行工况下相变储热器的储/放热性能。结果表明:添加0.5%CMC和2%DHPD的相变储热复合材料有效改善了纯SAT的相分离严重和过冷度大的问题,具有良好的热稳定性,多次循环后复合样品的相变焓为258 k J?kg~(-1),相变温度为57℃,过冷度在2℃以内;相变储能热水系统在不同放热工况下出口水温度均超过50℃,放热过程中相变材料温度变化平稳,储热器的储放热效率高于90%,放热功率大于10 k W,且随着入口水温下降,放热功率、放热量及储放热效率都提高,相变储热器的储能密度是传统水箱的2.6倍。
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 hydrate salt, 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 stable performance 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 transition temperature, supercooling and phase separation were analyzed. Finally, a high-density heat reservoir was built by using the modified PCM and a latent heat storage water system was set up. The charging and discharging performance 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℃, respectively. The modified PCM had good cycling stability and its supercooling degree was smaller than 2℃. In addition, the output water temperature of the latent heat storage system under different cooling conditions can be heated up to over 50℃. The efficiency was higher than 90% and the heating power was as high as 10 k W. The heating power, energy storage capacity and thermal storage efficiency increased with the decrease of the inlet water temperature. The system has good charging and discharging performance and its volume heat storage density is 2.6 times as higher as traditional water tank.
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 hydrate salt, 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 stable performance 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 transition temperature, supercooling and phase separation were analyzed. Finally, a high-density heat reservoir was built by using the modified PCM and a latent heat storage water system was set up. The charging and discharging performance 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℃, respectively. The modified PCM had good cycling stability and its supercooling degree was smaller than 2℃. In addition, the output water temperature of the latent heat storage system under different cooling conditions can be heated up to over 50℃. The efficiency was higher than 90% and the heating power was as high as 10 k W. The heating power, energy storage capacity and thermal storage efficiency increased with the decrease of the inlet water temperature. The system has good charging and discharging performance and its volume heat storage density is 2.6 times as higher as traditional water tank.
引文
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[20]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.
[21]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.
[22]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.
[23]HAMMICK D L,GOADBY H K,BOOTH H.CLXXV-Disodium hydrogen phosphate dodecahydrate[J].Journal of the Chemical Society,Transactions,1920,117:1589-1592.
[24]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.
[25]SANDNES B,REKSTAD J.Supercooling salt hydrates:stored enthalpy as a function of temperature[J].Solar Energy,2006,80(5):616-625.
[2]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.
[3]SHARMA S D,SAGARA K.Latent heat storage materials and systems:a review[J].International Journal of Green Energy,2005,2(1):1-56.
[4]汪意,杨睿,张寅平,等.定型相变材料的研究进展[J].储能科学与技术,2013,4:362-368.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.
[5]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.
[6]PIELICHOWSKA K,PIELICHOWSKI K.Phase change materials for thermal energy storage[J].Progress in Materials Science,2014,65(10):67-123.
[7]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.
[8]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.
[9]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.
[10]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.
[11]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.
[12]孟令然,郭立江,李晓禹,等.水合盐相变储能材料的研究进展[J].储能科学与技术,2017,6(4):623-631.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.
[13]苑坤杰,张正国,方晓明,等.水合无机盐及其复合相变储热材料的研究进展[J].化工进展,2016,35(6):1820-1826.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.
[14]张仁元.相变材料与相变储能技术[M].北京:科学出版社,2009.ZHANG R Y.Phase Change Material and Phase Change Energy Storage Technology[M].Beijing:Science Press,2009.
[15]张雪梅,蔡路茵,苏忠杰,等.超声波对三水醋酸钠相分离及结晶的影响[J].化工学报,2010,61(1):104-108.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.
[16]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.
[17]LANE G A.Phase change materials for energy storage nucleation to prevent subcooling[J].Solar Energy Material and Solar Cells,1991,27:135-160.
[18]方玉堂,金策,梁向晖,等.三水醋酸钠/甲酰胺复合相变材料的制备及性能[J].化工学报,2015,66(12):5142-5148.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.
[19]徐建霞,柯秀芳.CH3COONa·3H2O相变储能性能研究[J].材料开发与应用,2007,22(6):24-27.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.
[20]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.
[21]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.
[22]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.
[23]HAMMICK D L,GOADBY H K,BOOTH H.CLXXV-Disodium hydrogen phosphate dodecahydrate[J].Journal of the Chemical Society,Transactions,1920,117:1589-1592.
[24]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.
[25]SANDNES B,REKSTAD J.Supercooling salt hydrates:stored enthalpy as a function of temperature[J].Solar Energy,2006,80(5):616-625.