温室多壁碳纳米管芒硝基相变材料储能性能

Energy storage properties of mans nitro phase transition materials of multi-walled carbon nano-tubes of greenhouse

该文对比不同温度下强酸处理多壁碳纳米管(multi-walled carbon nanotubes,MWCNTs)对其表面结构改性,并以物理分散制备出含MWCNTs的十水硫酸钠基复合相变储能材料。探讨不同酸化温度下MWCNTs对十水硫酸钠基复合相变储能材料的过冷和相分层影响。并对其比热,导热系数及相变潜热特征进行分析。结果表明:酸化处理后MWCNTs产生羧基;添加质量分数1%的120℃酸化后的MWCNTs的A、B两种十水硫酸钠基复合相变储能材料过冷度降低最大;添加酸化处理后的MWCNTs的十水硫酸钠基复合相变储能材料相容性较好;含120℃酸化后的1%的MWCNTs的A、B两种十水硫酸钠基复合相变储能材料比热及导热系数在相变温度点附近都达到最大,分别为5.095 mm2/s和0.932 5 w/mk、4.235 6 mm2/s和0.941 3 w/mk;含质量分数1%的120℃酸化处理的MWCNTs的B类复合相变储能材料较A类的潜热值大,其分别为143.6 J/g,97.42 J/g;该试验表明含1%MWCNTs-B相变储能材料更适合应用于温室。

It is significant to study low temperature phase change materials（PCM） widely used in hothouses. The performance of low temperature sodium sulfate decahydrate based PCM composite affects hothouse temperature directly.Sodium sulfate decahydrate based PCM composite has suitable phase change temperature, but presents supercooling and phase stratification phenomenon. These problems restrict its practical application. The result of related study indicated that the heat conductive material had a certain influence on supercooling and phase stratification of PCM. We studied that the effect of nano-powders of sodium sulfate decahydrate on subcooling and phase stratification, of which the nano-carbon had the better effects on sodium sulfate decahydrate′ s supercooling and phase stratification. This paper explored the effect of multi-walled carbon nano-tubes（MWCNTs） with high thermal conductivity on 2 kinds of sodium sulfate decahydrate based PCM composites, named PCM A and PCM B. PCM A consisted of 90wt% Na2SO4·10H2O and 10wt% KCl. PCM B consisted of 86.4wt% Na2SO4·10H2O, 9.6wt% Na2CO3·10H2O, and 4wt% Na Cl. Firstly, MWCNTs was modified on surface by acid treatment at 90, 120 and 140 ℃ respectively, in order to obtain good compatibility with PCM A and B. Fourier transform infrared spectroscopy was used to detect the acid-treated MWCNTs and the surface functional groups on the MWCNTs were analyzed. Low vacuum scanning electron microscope was used to observe the surface morphology of acid-treatment MWCNTs. The acid-treated MWCNTs were added into PCM A and B by physical dispersion method. The time dependence of the temperature of PCM A and B containing acid-treated MWCNTs or not was recorded by date acquisition instrument to explore the effects of acid treatment temperature and mass fraction of MWCNTs on the degree of supercooling of PCM. The phase stratification phenomenon was photographed and investigated. The specific heat and thermal conductivity were measured by thermal constant analyzer. And the thermal conductivity and specific heat of thermally conductive material added into the PCM A and B were analyzed. The latent heat of PCM was analyzed by different scanning calorimetry measurements. Latent heat value directly affects the size of the heat storage capacity of the material. The results indicated that carboxyl group was formed in MWCNTs after acid treatment, which could improve the compatibility between MWCNTs and PCM A or B. By the scanning electron microscope, the surface topography change of the MWCNTs without oxidization and the MWCNTs with the surface modified by acid treatment at 90 ℃ was not obvious. And the MWCNTs with the surface modified by acid treatment at 120 ℃ had slight agglomeration. The MWCNTs with the surface modified by acid treatment at140 ℃ had serious agglomeration and shear break. When 1wt% acid-treated MWCNTs at 120 ℃ were added, both of PCM A and B showed low degree of supercooling. Their specific heat and thermal conductivity reached the maximum, which were5.095 mm2/s, 0.932 5 w/mk and 4.235 6 mm2/s, 0.941 3 w/mk respectively in the vicinity of the phase transition temperature. Abrupt change of specific heat of the phase change material at this point showed that mutations occurred for latent heat material itself. The increase of thermal conductivity showed that the heat transfer effect of phase change energy storage material was enhanced in the process of heat absorption and heat transfer. Besides, PCM B containing 1wt%MWCNTs acid-treated at 120 ℃ had higher latent heat than PCM A. They were 143.6 and 97.42 J/g respectively. These experiment results indicate that the PCM B containing 1wt% MWCNTs is more suitable for hothouse application.