Preparation And Thermal Storage Properties Of Composite Phase Change Materials Based On Paraffin

Paraffin is a typical organic phase change material,especially suitable for the temperature range of 0-90 ?,with such characteristics as higher latent heat,no supercooling and phase segregation,stable performance and no corrosion etc,but due to the disadvantage of the lower thermal conductivity coefficient,its heat transfer rate is affected in the process of phase change.Moreover,in the use of paraffin as phase change material,since its phase change temperature usually doesn't exactly match with the operation temperature of latent heat storage system,and the single paraffin cannot satisfy the requirements of building applications in the performance comparatively well.Therefore,the preparation and heat storage performance investigation of composite phase change material based on paraffin have more important practical value.In allusion to the disadvantages of the single paraffin such as lower thermal conductivity coefficient and it cannot satisfy the requirements of building applications comparatively well,the preparation,performances and heat transfer analyses in the process of phase change for the OC-LA composite phase change material were researched,and the nano-copper of high thermal conductivity was added to solve the problem with lower thermal conductivity coefficient of this composite phase change material,and the experimental measurements and investigation on its heat storage performance and phase change process were made.The main contents of the whole investigation are as follows:1.The preparation,performances and thermal stability investigation of the OC-LA composite phase change material.Firstly the OC-LA composite phase change material was prepared with a melting method by the octadecyl(OC)and lauric acid(LA).Then the phase change process of the OC-LA composite phase change material was measured by using the thermocouples installed in the test tubes,DH3816 Temperature Testing Analytical System and the computer with related software.The main thermophysical parameters including phase change temperature,latent heat,thermal conductivity coefficient and specific heat were measured by using NETZSCH STA449F3 Differential Scanning Calorimeter(DSC)and DRE-2C Thermal Conductivity Testing Instrument,and the experiment of the repeated melting-solidification cycles was carried out to verify the thermal stability of the OC-LA composite phase change material.The experimental results showed that,the phase change temperature and latent heat of the OC-LA composite phase change material were changed as the change of the molar ratio of the octadecyl(OC)and lauric acid(LA),the OC-LA composite phase change material had the lowest eutectic point,the corresponding mole ratio was OC:LA=0.572:0.428,and the lowest eutectic temperature was 21.51 ?.The thermal conductivity coefficient of the OC-LA composite phase change material had an inversely proportional relationship with its phase change temperature,when its phase change temperature was decreased,its thermal conductivity coefficient was raised.For the same composite phase change material,the thermal conductivity coefficient was enhanced as the temperature was increased,after the temperature was raised to a certain stage,since heat transfer was stable,its thermal conductivity coefficient became approximately constant.The OC-LA composite phase change material with the mole ratio of 6:4 had the suitable phase change temperature and latent heat,whose magnitudes were 24.29 ? and 176.8 kJ·kg-1 respectively,the composite phase change material had a comparatively good thermal stability after the experiment of 210 melting-solidification cycles.2.The preparation,performances and thermal stability investigation of OC-LA/nano-copper composite phase change material.The OC-LA composite phase change material with the mole ratio of 6:4 was selected as a research object,the OC-LA/nano-copper composite phase change material was prepared by the means of physical and chemical dispersion method.The main thermophysical parameters including phase change temperature,latent heat,thermal conductivity coefficient and specific heat were measured by using NETZSCH STA449F3 Differential Scanning Calorimeter(DSC)and DRE-2C Thermal Conductivity Testing Instrument,and the experiment of the repeated melting-solidification cycles was carried out to verify the thermal stability of the OC-LA/nano-copper composite phase change material.The experimental results showed that,the effect of the presence of nano-copper on phase change temperature of the composite phase change material was not obvious,but the effect on its latent heat was more obvious,and the maximum decrease extent was 12.2 kJ·kg-1.The thermal conductivity coefficient of OC-LA/nano-copper composite phase change material in solid or liquid state was all raised as the nano-copper mass fraction was increased,when the nano-copper mass fraction was more than 3%,its thermal conductivity coefficient was no longer increased.The thermal conductivity coefficient of the OC-LA/nano-copper composite phase change material was enhanced as the temperature was increased,after the temperature was raised to 50 ?,since heat transfer was stable,its thermal conductivity coefficient became approximately constant.The addition of nano-copper could improve heat transfer performance of the composite phase change material effectively,the addition of nano-copper mass fraction of 1.5%was comparatively suitable,and this composite phase change material had a comparatively good thermal stability after the experiment of 210 melting-solidification cycles.3.Simulation analyses of heat transfer process of the two composite phase change materials.The ANSYS software was used for analyzing the heat transfer process of the OC-LA composite phase change material and OC-LA/nano-copper composite phase change material,the research results showed that,the addition of nano-copper could improve heat transfer performance of the composite phase change material effectively,the OC-LA/nano-copper composite phase change material had a comparatively better heat transfer rate than that of the OC-LA composite phase change material.The research and achievements in this paper can solve the problem of the single paraffin such as lower thermal conductivity and it cannot satisfy the requirements of building applications comparatively well,which will provide comparatively reliable experiment evidence and technical foundations for the utilization in the heating of the industrial and civil building structures.