Study On Thermal Properties Of Phase Change Energy Storage Materials

Phase change materials (PCMs) can store energy and discharge energy by phasetransition of PCMs, which is called latent heat storage. PCMs have the advantages ofsmaller temperature difference between storing and releasing heat, and higher storagedensity, and easily controlled. PCMs have been applied in the field of solar energystorage, building heating, waste heat utilization, agriculture.In this paper, heat and cooling curves of lauric acid、stearic acid and palmitic acidwere investigated by using time-temperature curve method. Their liquid thermalconductivities are0.4265W m K、0.6175W m K and0.4590W m K respectively; and the corresponding solid thermal conductivities are0.2379W m K、0.4184W m K and0.2612W m K. DSC test was used toanalyse thermodynamic properties. The result shows that the phase changetemperatures of lauric acid、stearic acid and palmitic acid are43.7℃、62.4℃、67.7℃, with phase change enthalpies151.9J/g、184.7J/g、224.3J/g correspondingly.The eutectic mixtures (LA-SA、OC-LA、LA-PA、OC-PA、CA-LA and HD-PA)were prepared by using phase diagram method. Their phase chang temperatures are31.6℃、23.4℃、33.6℃、26.6℃、16.0℃and42.2℃, with mass fraction70.5%、65.6%、67.1%、70.3%、61.1%and64.5%correspondingly. Phase change temperaturesof eutectic mixtures can also be obtained by DSC analysis. they are32.1℃、23.2℃、35.6℃、28.2℃、19.6℃and45.3℃respectively, which are consistent with the resultsof phase diagram method. The corresponding phase change enthalpies are176.3J/g、162.3J/g、155.3J/g、181.6J/g、115.8J/g and199.2J/g respectively.As to low conductivity characteristics of organic phase change materials,activated carbon and graphite are added to single phase change materials and eutecticmaterials seperaturely. The result shows that the heat transfer enhancement is veryobvious, and the effects are different to different kinds of phase change materials. Theinfluence of heat medium temperature on heat transfer of single phase changematerials and eutectic materials were investigated. The result shows that the heattransfer is enhanced with increasing heat medium temperature during melting process,on the other hand, the heat transfer is enhanced with decreasing heat mediumtemperature during solidification process. Moreover, the influence of heat mediumvolume flowrate on heat transfer of single phase change materials and eutectic materials were investigated. The result shows that Renault coefficient of fluid isincreased, and turbulence degree of fluid is strengthened. At the same time, heattransfer of materials is enhanced, and phase change time of materials is shortened.