The High Temperature Phase Change Heat Storage Materials, Preparation And Properties Of,

Phase change heat storage,especially the phase change from solid state to liquid state,has the advantages of high heat storage density per unit weight (volume),narrow range in temperature variation around the phase change point for heat absorption and release.Nowadays it has been widely used in many fields such as solar energy dynamics in outer space,thermal control in semiconductor industry,airconditioning cooling system and temperature modulation of constructions.Due to the shortage of energy resources the research related to the technology and fabrication of phase change materials (PCMs)has been the hot topic recently.As one of the biggest energy resources consumer,China is facing the significant problem of low usage factor of energy resources.For example,the fuel burner whose energy consumption accounts for 20%of the total energy consumption in China has the thermal efficiency less than 50%.The burners in non-ferrous metallurgical industry and silicate industry only have the thermal efficiency less than 30%because the periodicity of productivity results in the intermittently remnant heat and therefore the low heat recycle rate.In this thesis,based on the practical reduction of the energy resources consumption in China,the novel and high performance composite energy storage materials which combine the sensible heat energy storage material with the phase change energy storage material have been successfully synthesized and detailed studied.Such composite energy storage materials take the advantages of both materials while avoid their disadvantages,and therefore enhance the recycle rate of remnant heat and thermal efficiency.The thesis consists of following five parts:1.Based on the well-established phase change theory combining with the character of composite PCMs,the solidification and melt during the phase change were investigated with the aid of phase diagram.The detailed application of phase diagram was also analyzed for the preparation of composite phase change materials. 2.With regard to the application of industrially remnant heat recycle,the thermal properties of the base materials and the PCMs were examined.The chemical capability between the base material and PCMs was simulated by HSC5.1 software.The suitable high temperature PCMs and base material were preliminarily selected.Through the repetitious experiment the compatible PCMs and base materials were preferentially determined,i.e.the PCMs such as K₂CO₃,Na₂SO₄,KCl or Al with the base materials such as Al₂O₃,MgO or porous Ni.3.Scanning electron microscope(SEM),X-ray diffraction,Differential scanning calorimetry/ Differential thermal analysis(DSC/DTA),Energy dispersive spectroscopy(EDS)were used to explore the properties of synthesized composite heat energy storage materials.In the synthesized melting salt/metal base composite PCMs,the melting salt were uniformly distributed in the porous network-shaped metal base which separates the PCMs as numerous smaller heat energy storage unit.These small heat energy storage units not only enhance the heat absorption and release but prevent the melting PCMs outflowing due to the capillary tensions.Similarly in the prepared melting(or metal)/ ceramic base,the melting salt were also uniformly distributed in the ceramic base.The good capability between the melting salt(or metal)and ceramic base also makes the heat energy storage material more stable and more efficient.4.Powder-pressured pallet method and porous ceramic base(or metal base)melting method were used to prepare the heat energy storage materials. Three types of high temperature phase change composite heat energy storage materials were prepared corresponding to different applications,i.e. metal/ceramic base,melting salt/ceramic base and melting salt/metal base.The effect of preparation parameters such as sintering temperature,sintering time duration and pressure to form pallet and so on were also investigated.5.How to choose the suitable phase change material is the key problem for the remnant heat at certain temperature in the real application.The sensible heat and phase change energy storage systems were both thermodynamically optimized according to the minimum enthalpy theory.The derivation and analysis of optimum phase change temperatures for one phase change heat storage system or various classified systems provide the theoretical reference for the proper selection of PCMs in the real application.