Thermal Physical Properties Of Fly Ash-based Shaped Stable Phase Change Thermal Storage Materials

Human production and life are closely related to the use of thermal energy.In order to improve energy utilization efficiency and solve the mismatch between thermal energy supply and demand,the development of high-performance thermal storage materials is imminent.Nitrate is one of the widely used high-performance phase change materials,with low cost and high heat storage density,which has a promising application in solar thermal utilization and industrial waste heat recovery,but there are still problems such as liquid leakage.However,the preparation of matrix materials in existing shaped stable phase change thermal storage materials requires the consumption of large amounts of energy and natural minerals.In order to further solve the problem of nitrate molten salt liquid leakage,reduce the preparation cost of the shaped stable phase change thermal storage materials and save natural resources,this paper selects nitrate(sodium nitrate and solar salt)as the phase change material and solid waste fly ash with huge reserves and low reuse rate as the matrix material,and prepares the shaped stable phase change thermal storage materials by mixing-briquetting-sintering preparation method.The chemical composition,thermal properties,chemical compatibility and cold-thermal cycling characteristics of fly ash and shaped stable phase change thermal storage materials were investigated by XRD,FT-IR,SEM,DSC and thermal conductivity analyzer.The specific research of the paper is as follows.(1)Thermal physical properties of fly ash/sodium nitrate shaped stable phase change thermal storage materials.Firstly,the chemical composition,microscopic morphology and specific surface area of the matrix material fly ash were characterized and its feasibility was discussed.After that,the related study on the prepared shaped stable material showed that the optimum pressure of fly ash/sodium nitrate shaped stable phase change thermal storage material is 15 MPa and the sintering temperature is 350 ?.The fly ash has more inter-particle pores and good compatibility with sodium nitrate molten salt.When the content of fly ash was 40 wt%,the shaped stable phase change thermal storage material was intact,without cracks and no leakage of molten salt,and SEM showed the existence of pores between fly ash particles.The phase change temperature of the 4:6 fly ash-sodium nitrate shaped stable phase change material was 300.3 ?,the latent heat of melting was 85.6 J/g,and the thermal conductivity was 0.4531W/(m·K).With the increase of fly ash content,the latent heat and thermal conductivity of the composites decreased.After 100 cold and hot cycles,the 4:6 fly ash-sodium nitrate shaped stable phase change material showed a 9.3% reduction in enthalpy and a 3.41% mass loss,and showed good cycling stability in terms of appearance and chemical compatibility.(2)Thermal physical properties of fly ash/solar salt shaped stable phase change thermal storage materials.The molten salt-solar salt(60 wt% sodium nitrate-40 wt% potassium nitrate)with low melting point and high thermal conductivity was selected as the phase change material and fly ash as the matrix material,and the shaped stable phase change thermal storage materials with different mass ratios were prepared.The results showed that the optimum pressure of fly ash/solar salt shaped stable phase change thermal storage material is 15 MPa and the sintering temperature is 260 ?.The 5:5 fly ash-solar salt and 4:6 fly ash-solar salt shaped stable phase change thermal storage materials were complete,and the SEM analysis showed that the overall structure of the two thermal storage materials was embedded and there were no pores between fly ash particles;the phase change temperatures of the two were 212.1 ? and 210.6 ?,the latent heats of melting were 54.4 J/g and 64.1 J/g,and the thermal conductivities were 0.5764W/(m·K)and 0.6471 W/(m·K),respectively.The enthalpy reductions of both were 6.7% and5.2%,and the mass reductions of both were 2.3% and 1.98%,respectively,when the samples were treated with 100 times of hot and cold cycles.The shaped composite phase change thermal storage material prepared by using solar salt as the phase change material has good thermal stability and is expected to be a low-cost medium and high temperature shaped composite phase change thermal storage material.