Study On Thermal Properties And Packaging Materials Of Complex Phase Change Energy Storage Materials

Phase change energy storage material can solve the supply and demand of energy on problem of time and space does not match,because it can absorb or release heat during the phase change process to control the temperature and storage energy.Sodium sulfafe decahydrate as a salt hydrate phase change material exists supercooling degree and stratification.At the same time,the solid-liquid phase change process causeleakage problems with improperlypackage,which need further research.The first part using composite phase change energy storage materials?PCM?,such as Cu-Na₂SO₄.10H₂O,Al-Na₂SO₄.10H₂O,and C-Na₂SO₄.10H₂O,were prepared by the method of physical and chemicaldispersion.The effect of nano Cu,nano Al,and nano C on the undercooling and phase stratification ofNa₂SO₄.10H₂O was investigated.The thermal conductivity,thermal diffusivity,specific heat,latentheat,and morphology of the C-Na₂SO₄.10H₂O composites were analyzed.The results show that theaddition of aforementioned three nano materials makes the supercooling property decrease significantly to1.8?,2.1?,1.2?,respectively.Nano Cu powder and Nano Al powder PCM tend to lose efficacyafter a phase change circulation,while C nano powder PCM has no obvious stratification phenomenon.Besides,with the increase of C nano,the coefficient of thermal conductivity of PCM is increased,and thethermal diffusivity increases as well,while the specific heat is decreased.The thermal conductivity ofcomposite materials in the melt and crystallization state increases with the increase of temperature,andthe latent heat value of the 4% C-Na₂SO₄.10H₂O composite after 50 times phase change cycle is changed to 188.3 J/g.The influence of MWCNTs was modified on surface by different acid temperayure on supercooling and phase separation of Na₂SO₄.10H₂O was investigated.And the specific heat,thermal conductivity and latent heat of phase change were analyzed.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 at 140 ? 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 were 5.095 mm2/s,0.932 5 w/mk and 4.235 6 mm2/s,0.9413 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.The second part using the corrosion kinetics of metal packaging materials by sodium sulfate decahydrate based composite phase change material were investigated by weight-loss method.The results show that the corrosion resistance of stainless steel is best,and the pure copper is worst.Order of corrosion resistance is: stainless steel 304>stainless steel 201>1060 aluminum>aluminum alloy 5052>aluminum alloy 6061 >aluminum alloy7075>brass>copper.The pitting corrosion is the main corrosion form for copper and brass.For copper,the corrosion hole is consisted of Cu2 O,the presence of adsorption oxygen competing with Cl-accelerates the corrosion.Brass also exists pitting corrosion,while the reaction of brass and phase change materials,the formation of material adhesion on the surface of brass.Aluminum shows pitting corrosion,of which the corrosion product is cracking like and adhere to the substrate surface.Copper,brass and aluminum alloy are not suitable for the packaging materials for phase change energy storage material.Stainless steel 201 and 304 presentes good resistance to corrosion,are suitable as metal-based packaging materials for storage phase change material.The thirdpart uses inorganic package material to packagesodium sulfafe decahydrate based phase change.Using temperature recorder to test the change of temperature in phase change greenhouse and ordinary greenhouse.On maximum temperature in the daytime,the temperature in the phase change greenhouse is lower than ordinary greenhouse.On the minimum temperature in thenight,the temperature in the phase change greenhouse is higher than ordinary greenhouse.So the PCM has good application in the greenhouse.