The Selection And Performance Research Of PCMs' Container Materials Used For Solar Energy

Metal phase change material(PCMs) plays an important role in the application of energy storage technology at medium-high temperature,because they have the following features:high energy storage density,good thermal stability,high thermal conductivity,small subcooling degree and segregation and so on.As one of the PCMs,eutectic Al-Si storage alloy has successfully been developed and utilized in various heat storage applications.In the field of solar thermal power generation,Al-Si alloy is nearly ideal PCMs at medium-high temperature.But in practice,the molten Al-Si metal fluid can corrode metal containers by scour and the formation of intermetallic compound etc,thinning the metal containers and then resulting in intensity decrease and the final failure,which seriously restrain the application of phase change energy storage.Therefore,it is very important that a stable energy storage power generation should be provided and application of PCMs should be improved by seeking the affordable and safe container marweial and practical coatings'solutions.In this thesis,the Al-Si alloy(content of silicon was 12.07%) were used for PCMs.Corrosion resistant Al-Si(12.07%) of gray irons and them with brushing paint coatings and the ceramics were researched by repeatly heating at 495～620℃.The following conclusions were found by studying corrosion resistant aluminum of gray irons at 495～620℃.Fe2Al5 ang FeAl3 were found in the gray iron alloy layer of corrosion.Under the action of organization into stress and thermal stress,Fe2Al5 were broken and dissolved,resulting the erosion happened on the surface of gray irons.It was found that the slope of thickness loss and weight loss unit area were getting smaller after 600 hours of corrosion.The elements Al and Si were infiltrated into surface of gray irons through spectrum analysis.As the distance increases with the molten Al,content of Al were decreased and almost non-existent within the gray irons.To reduce the corrosion of Al-Si on the surface of gray irons,four coatings were deployed.By testing their performance,the following conclusions were explored.1) After the thermal shock experiment,all coatings did not fall off and blistering occurred,but had a good thermal shock resistance.2) According to GB/T-9286,four coatings all had good bonding strength,such as adhesion of T3 solution achieved to 0,and adhesion of Tl,T2andT4 achieved to 1.3) By testing thermal conductivity of four coatings and the original sample by HotDisk,they were little difference between the thermal conductivity,and did not affect heat transfer performance between Al-Si storage alloys and gray irons.Through thermal cycling and thermal stability tests between gray irons brushing coatings and Al-Si storage alloys,the following conclusions were explored.1) Brushing coatings to the surface of gray irons for corrosion test,corrosion layer was thinner and corrosion rate was less than before.Especially,corrosion layer thickness of T1 coating solutions were thinner 68.55% than gray irons without coating.Same as above,T2 were thinner 74.12%,T3 were thinner 77.05%,T4 were thinner 77.23%.So,T3 and T4 coatings solutions were better than T1 and T2.2) The melting point of Al-Si storage alloys contactings with T1-T4 coatings had increased by 0.67%,0.66%,0.64%,0.61%.But,the latent heat of Al-Si storage alloys correspondly decreased 9.38%,9.27%,9.14%,9.09%.On the whole, the impact on these coatings of latent heat was very limited.Therefore,basing on experimental datas above,selecting them as PCMs container of solar energy should be feasible.In addition,by studying corrosion-resistant Al-Si to ceramics R-SiC and Si3N4-SiC at 495～620℃,the following results were revealed.Relative to gray irons,R-SiC corrosion thickness was reduced by 91.96%,and Si3N4-SiC corrosion thickness was reduced by 92.10%.Ceramic material's surface was not wetted by molten Al-Si or did not react with them.Basing on the analysis above,the area and time of ceramic surface contacting with molten Al-Si were relatively fewer than other gray irons materials.So,the ceramics's resistance to molten Al-Si was better than gray irons covered with T3 or T4 coatings.Relativing to R-SiC,the ceramics Si3N4-SiC selected for container material of solar energy storage alloy had a certain cost benefits.Therefore,selecting Si3N4-SiC,T3 and T4 coatings of gray irons as the container materials,not only can resist the corrosion of molten Al-Si, but aslo increase equipment life, more to further promote the application of PCMs.