Study On The Improvement Of Supercooling And Thermal Conductivity Of Erythritol As Phase Change Materials

Erythritol(ET)with an appropriate phase transition temperature(～118 ~oC)has the advantages of high energy storage density,non-corrosiveness,etc.It is a promising phase change material(PCM)in the field of medium temperature energy storage,which is widely used in solar energy storage,industrial waste heat recovery,clean heating and other fields.However,erythritol has severe supercooling and its thermal conductivity is relatively lower.These shortcomings limit its application in energy storage.In this paper,the ET is used as heat storage material,and the organic salt is used as nucleating agent because it can form intermolecular hydrogen bond with erythritol,which breaks the balance between the internal molecules of erythritol and promotes the release of latent heat.Therefore,the supercooling can be inhibited.Secondly,the thermal conductivity of ET will be enhanced through adding expanded graphite(EG)as thermal strengthening material.Lastly,appropriate PCMs are selected to adjust its phase change temperature through the eutectic theory,so that it can be used in different thermal environments.The major conclusions of this thesis are as follows.Nine nucleating agents were selected to inhibit the supercooling of erythritol.Experimental results reveal that calcium pimelate(Ca Pi)as a nucleating agent has a positive influence on the supercooling elimination of erythritol measured by Temperature-time curves.The optimal Ca Pi/erythritol composite phase change material(CPCM),with the Ca Pi mass percentage of 1%,melts at 118 ~oC and the supercooling degree of erythritol drops to 0.6 ~oC.The latent heat of CPCM is 344.86 J/g,and it remains above 300 J/g after 50 cycles.The ET/expanded graphite(EG)CPCMs with mass fraction of 1%—8%were prepared.It can be found that the supercooling degree of 2%EG/ET CPCMs gradually decreased with the increase of cycle times,and the fusion latent heat is higher.In order to explore the influence of Ca Pi and EG on erythritol,the2%EG/1%Ca Pi/ET CPCM was prepared,of which the melting latent heat is 352.66 J/g,the supercooling is 10.29 ~oC and the thermal conductivity is 1.287 W/(m·K),which is52.5%higher than that of pure erythritol.The solidification temperature is above 98.5~oC during the cycling,which indicates that the CPCM has good thermal reliability in terms of the changes in thermal properties.Therefore,it is a kind of potential medium temperature CPCM.The effect of sebacic acid(SA)on the phase transition temperature of erythritol was investigated.Experimental results show that the SA/ET binary phase transition system with different mass fractions can form heat storage materials with a temperature range of 105 ~oC to 132 ~oC,which has high thermal utilization value.Then,the regulating influence of D-mannitol(DM)and magnesium chloride hexahydrate(MCH)on the phase transition temperature of erythritol were verified.When the mass fraction of DM is less than 20%,a heat storage material with cooling point ranging from 80.6 ~oC to118.2 ~oC is formed.When the mass fraction of MCH is less than 15%,a heat storage material with cooling point range of 64.6 ~oC to 118.2 ~oC is formed.The CPCMs broaden the application range of erythritol,which can be used in heating and domestic hot water production and other fields.