Preparation Of Composited Phase Change Material And Charging Experiment For The Cascade Thermal Storage Served In The Cold Region Of Inner Mongolia

With the development of society,people’s living requirements are constantly improving,and the building energy consumption is constantly increasing.The application of renewable energy can alleviate the problem of traditional energy shortage,which is the main trend of energy development.However,most renewable energy source is intermittent and unstable,and the phase change heat storage technology is an effective way to solve the intermittence of renewable energy source.Most areas of Inner Mongolia are cold region in the building climate zone,with higher heating energy consumption.On the other hand,Inner Mongolia is rich in solar energy resources,which is more suitable for using solar energy for clean heating.Due to the low efficiency of the heat storage of the heat storage system due to the low thermal conductivity of the phase change material.In recent years,domestic and foreign scholars at home and abroad have improved the efficiency of the heat storage system by improving the thermal conductivity,increasing the heat transfer area of the heat storage system,and improving the temperature difference between the heat transfer working matter and the material.In this paper by adding high thermal conductivity of expanding graphite preparation composite phase transition materials,application fins,cascade heating means to improve the heat storage efficiency of the system,explore the influence of different heat transfer medium inlet parameters on the heat storage system,finally match the change of cascade heat storage system configuration,analyze the typical day heat storage process.Stearic acid and lauric acid are chosen in this thesis to form a cascade phase change heat storage material group.The thermal conductivity of the phase change material is improved by the addition of thermally conductive expanded graphite.The melt blending method is used to prepare the composite phase change material in order to detect phase change temperature,phase change latent heat,thermal conductivity,and other thermophysical performance parameters.Expanded graphite stearic acid has a phase transition temperature of 65°C～75°C,a phase transition latent heat of 210.91J/g,and a thermal conductivity of 0.742W/(m·K).Expanded graphite lauric acid has a phase transition temperature of 43°C～50°C,a phase transition latent heat of 202.41J/g,and a thermal conductivity of 1.362W/(m·K).The performance of the cascade phase change heat storage system was analyzed experimentally.The influence of inlet parameters of different flow rate and temperature of heat exchange medium on the melting rate of phase change materials(PCMs)was investigated under certain conditions,the results show that the melting rate of the composite phase change material near the inlet of the heat exchange medium is faster,the flow rate of the heat exchange medium increases from 6L/min to 14L/min,and the phase change time in the first-stage heat accumulator decreases by 15%,the phase change time in the secondstage heat accumulator decreases by 6%.When the heat exchange medium’s temperature rises from 90°C to 110°C,the phase change time in the first-stage heat accumulator is shortened by 61% at most and that in the second-stage heat accumulator is shortened by 31%at most.By changing the heat exchange medium flow to match the change of solar radiation intensity in one day,the spring equinox and winter solstice are selected as typical days for analysis and research.The radiation intensity of spring equinox is high,and the cascade heat storage system can complete phase change heat storage The winter solstice irradiation intensity is low,the duration is short,the heat storage material can’t complete the phase transformation,and the design matching heat exchange mass flow change is unreasonable,which can’t meet the heat storage requirements of the system.Therefore,the heat storage efficiency can be improved by increasing the heat exchange mass flow to meet the heat storage requirements of the system.This experimental study provides a certain reference for the cascade heat storage technology suitable for the use of solar energy in the severe cold area of Inner Mongolia,and provides ideas for the subsequent practical use optimization.