Synthesis And Characteristics Of Organic Composite Phase Change Materials For Thermal Energy Storage With Enhanced Heat Transfer

Phase change materials have attracted increasing attention at home and abroad in recent years.They have the characteristics of constant temperature,large latent heat of phase change,stable performance and abundant reserves.Faced with the energy shortage,the supply and demand of energy are contradictory in many cases.The use of thermal energy storage technology is an important way to improve energy efficiency and protect the environment.This paper proposes an innovative method of combining organic phase change materials with different supporting materials so as to overcome the shortcomings like the volume change,supercooling and phase separation during phase transition process.The first chapter introduces the general situation of phase change technology,including the development background,principle,characteristics and research scope.In the second chapter,the binary organic eutectics/bentonite composite phase change materials,organic phase change material/metal foam composites,are prepared and analyzed in detail.In the third chapter,the preparation process and thermal physical properties of composites with organic alcohol as phase change material and high density polyethylene as matrix,strengthened by high thermal conductivity carbon fiber,are introduced.Thermal conductivity of polyvinyl butyral has been improved with the addition of graphene nanoplate.The physical and electrical properties of the composites are studied.1.Preparation and properties of organic composite phase change materials for energy storageBentonite-based composite phase change materials(CPCMs)were fabricated by the impregnation of fatty acid eutectics into bentonite clay.In the composites,the palmitic acid(PA)-stearic acid(SA)eutectics mixtures were undertook as phase change materials(PCMs)for thermal energy storage,and the bentonite were performed as the supporting material.Expanded graphite(EG)was employed for helping restrain the eutectic mixtures from leakage as well as improving thermal conductivity of the CPCMs.The differential scanning calorimetry(DSC)was adopted to assess the thermal properties of the composites,the results showed that the CPCMs have suitable melting temperature of around 54 ? with latent heat capacity of 89.12-163.72kJ/kg.Fourier transformation infrared(FT-IR)and X-ray diffractometer(XRD)were utilized to test the chemical structure and crystalline phase of the CPCMs.The scanning electron microscope(SEM)images revealed that the organic PCMs homogenously spread to the surface and interior of the bentonite.The thermal gravimetric analyzer(TGA)detected that the CPCMs were provided with good thermal stability.As the content of the EG increased,the leakage of the PA-SA eutectics reduced considerably.The results from the thermal conductivity meter(TCM)showed that the thermal conductivity of the CPCM with content of 5%EG reached to 1.51 W/(m.K)in liquid state and 1.66 W/(m.K)in solid state,which was nearly 5.6 times and 4.9 times higher than that of the CPCM without the EG.Experiments displayed that the thermal storage and release rates were noticeably enhanced by combining the EG into original CPCMs.The CPCMs maintained thermal properties after 50 heating-cooling cycling.It is envisioned that the satisfactory CPCMs maintain considerable prospects in thermal energy storage.Myristyl alcohol(MA)/metal foam composite phase change materials(CPCMs)were fabricated by vacuum melting infiltration.MA was used as the phase change material(PCM)and the metal foam was used as skeleton.Nickel foam and copper foam were both employed for comparison.Furthermore,effects of pore size of metal foam on thermal performances were analyzed.Thermal properties,including differential scanning calorimeter(DSC)test results and thermogravimetry analyzer results(TGA)were investigated and analyzed.As compared to latent heat of pure MA,the latent heat of CPCMs for the melting process decreases by 3-29%.TGA results showed that the composites have good thermal stability.Fourier transformation infrared spectroscope(FT-IR)and X-ray diffractometer(XRD)were used to determine chemical and crystalloid structure of the composites,respectively.Microstructures of the composites were analyzed by scanning electron microscope(SEM),and the results indicated that the PCM was well absorbed by the metal foam.Thermal conductivity of the composites was measured by thermal conductivity meter(TCM),and the results indicate that MA/metal foam composites have an improved thermal conductivity.2.Preparation and properties of polymer-based composite phase change materialsForm-stable phase change materials consisting of organic cetyl alcohol(CtA)and high density polyethylene(HDPE)were modified by carbon fiber(CF).Mass proportion of PCMs ranges from 70 wt%to 90 wt%.Cetyl alcohol(CtA)was chosen as the solid-liquid PCM and HDPE worked as the supporting material.The novel shape-stabilized composite phase change materials(CPCMs)were fabricated via impregnation of CtA into HDPE.In addition,the thermal conductivity of CPCMs was enhanced by carbon fiber(CF).The microstructure,crystalline phase and chemical structure were determined by scanning electronic microscope(SEM),X-ray diffractometer(XRD)and Fourier transformation infrared spectroscope(FT-IR).The results demonstrated that CtA was well impregnated into the HDPE.Differential scanning calorimeter(DSC)was utilized to analyze thermal properties of the composite phase change materials(CPCMs),and the results indicate that the CPCMs nearly melt at around 50 ? with a latent heat of 149.02-212.42 kJ/kg.Thermal gravimetric analyzer(TGA)confirmed that the CPCMs have an improved thermal reliability and the addition of CF contributed to a significant decrease in the leakage of CtA.The thermal conductivity meter(TCM)determined that the thermal conductivity of CPCM with 5wt%CF is 0.33 W/(m.K)and 0.47 W/(m.K)in liquid and solid state respectively,which is 1.25 and 1.22 times higher than that of original CPCM without CF.The experimental results indicate that the prepared CPCMs have prospects in thermal energy storage field.Polyvinyl butyral(PVB)composites were successfully fabricated using graphene as thermal conductivity enhancement filler.The novel composite was prepared via solution blending.Graphene nanoplates(GN)were added to modify thermal conductivity of PVB.Thermal conductivity meter(TCM)and thermo-gravimetric analyzer(TGA)were used to investigate thermal properties of the composites like thermal conductivity and thermal stability,respectively.Fourier transformation infrared spectroscope(FT-IR)and X-ray diffractometer(XRD)were used to analyze chemical structure and crystalline phase of the composites,respectively.Microstructure of samples was determined by scanning electronic microscope(SEM).The results from the thermal conductivity meter(TCM)showed that the thermal conductivity of sample with a content of 30(Wt%)GN can reach 4.521 W/(m.K),which is nearly 20.55 times higher than that of pure PVB.The heating and cooling rates of 30(wt%)GN sample are accelerated noticeably with an enhancement of 28%and 37%,respectively,over that of original PVB.The composites have appropriate ionic conductivities as encapsulation materials,which are generally lower than 10'5 S/m.It is forecasted that the prepared composites have considerable prospects in encapsulation of solar cells and cooling of electronic devices.