Preparation And Thermophysical Properties Of Novel Composite Phase Change Materials

The development and utilization of solar energy has solved the problem of the shortage of traditional fossil energy.Among them,photovoltaic power generation is one of the important ways,however,the photovoltaic system is less efficient at current stage.To improve the comprehensive utilization efficiency of solar energy and ensure the photoelectric conversion efficiency of photovoltaic cells,it is of great significance to carry out the waste heat recovery of the high-density heat flow generated by photovoltaic system.Heat storage during solid-liquid phase change has attracted much attention due to its advantages of almost constant temperature and high heat storage density during charging and discharging.The thermal properties of phase change material and the structure of heat storage unit are two important factors affecting the performance of thermal storage system.The development of high-performance shaped phase change materials has far-reaching significance for improving the heat storage and release efficiency.In addition,the structure of heat storage unit affects both the performance of thermal storage system and the ost of thermal storage system.Therefore,composite phase change material with high thermal conductivity would be developed,the correlation mechanism between the thermal physical properties and its constituent structure would be established,and a high-efficiency phase change thermal storage device would be designed to explore its heat storage characteristic.Hydrated salt has the advantages of large latent heat,wide source and low cost,while it exist large undercooling and serious corrosion characteristics to the container material.Thus,Alum/expanded graphite composite was prepared.The expanded graphite acted as nucleating agent and thermal conductive porous medium skeleton.And experimental and mechanistic studies on thermal properties and heat storage characteristics were carried out.In addition,the compatibility of composite with the metal material was studied and its compatibility with the container material is explored,Finally,relevant theoretical analysis of the corrosion mechanism was carried out.In order to expand the application range of Alum,experimental research found that the addition of effective melting point modifier can significantly reduce its melting point.The addition of Ala can effectively reduce the melting point of Alum.Sod is used as its nucleating agent and expanded graphite is acted as nucleating agent and thermal conductive porous framework.Alum-Ala/expanded graphite composite was prepared.The thermal properties of the prepared Alum-Ala/expanded graphite composite were measured by experiment.The experimental result showed that the melting point can be adjusted from 74.61 ° C to 91.11 ° C by adjusting the amount of Ala,greatly widening its application temperature range.And detailed theoretical analysis of its melting point modification mechanism was carried out.With the addition of expanded graphite,the thermal conductivity of Alum-Ala/Expanded graphite composite was enhanced by a factor of 21.9(relative to the original Alum-Ala),and the subcooling degree was reduced from 2.238 K to 1.866 K by the addition of Sod and expanded graphite.Since the organic phase change material has excellent thermal cycle stability during application and without supercooling and phase separation.However,it still exists the disadvantages of liquid mobility and low thermal conductivity.The AC/expanded graphite composite was prepared with AC as phase change thermal storage material,and the thermal properties of the composite were studied in detail.With the addition of expanded graphite,the thermal conductivity was increased to 6.159 W/m/K,and an effective thermal conductivity prediction method was established.The development of organic eutectic phase change materials is mostly concentrated on fatty acids and linear hydrocarbons which possessed relatively low melting temperature.Due to the excellent thermal properties of AC,low cost and excellent performance of SA,SA and AC were used to prepare SA-AC eutectic phase change material with mass ratio of 83:17.Then SA-AC/expanded graphite composite was prepared and thermal properties was measured in detail.The melting temperature and latent heat of fusion of the SA-AC eutectic phase change material are 66.35°C and 202.5 J/g,respectively,which indicated that the SAAC eutectic phase change material had excellent heat storage capacity and suitable for waste heat recovery.Theoretical analysis of phase change characteristics of SA-AC/Expanded graphite composite was carried out by the second law of thermodynamics.The structure of the heat storage unit is one of the important factors affecting the performance of heat storage system.A cylindrical serpentine phase change unit was designed.The OP80E/expanded graphite composite was used as heat storage carrier.The experiment and numerical simulation method were carried out to study the impact of the operating parameters and the thermal properties of the composite.To analyze the influence law,the average power is proposed to theoretically analyze its performance.