Investigation Of The Expanded Graphite/Erythritol Form-Stable Composite Phase Change Materials For Medium Temperature Thermal Energy Storage

In the future energy era,the proportion of concentrating solar power(CSP)generation is expected to increase gradually.If thermal energy storage(TES)can be introduced to solar systems,the problem of mismatching the solar energy supply and power demand can be solved,and the efficiency of the use of turbines and other energy equipment can be improved.In the development of medium temperature phase change heat storage,erythritol as a non-toxic,non-corrosive,non-polluting medium temperature phase change material(PCM)has a very broad application prospect.However,the low thermal conductivity and the high degree of supercooling restrict the application of erythritol.A form-stable erythritol/expanded graphite(EG)composite PCM for mid-temperature TES was successfully developed by an "impregnation,compression and sintering" three-step method.Five composite samples were prepared with the EG contents of 5 wt.%,8 wt.%,10 wt.%,12 wt.%and 15 wt.%.During the fabrication,erythritol and EG showed good chemical compatibility,and erythritol can be well absorbed in the worm-like porous structure of EG.After measuring the thermal properties,the thermal conductivity is increased from 0.72 W/(m·K)to 15.01 W/(m·K)and the freezing temperature is increased from 60? to 70? with the increase of the EG content from 0 wt.%to 15 wt.%.However,the melting temperature is decreased from 116? to 98?,the supercooling degree is reduced from 39.5? to 15.3? and the latent heat of the composite PCMs is reduced from 244.4 J/g to 198.3 J/g with the increase of the EG content.Furthermore,the 40 times charging-discharging cyclic performance of the form-stable composite PCMs was also tested on a supercooling test platform from room temperature to 1308.The charging time was obviously shortened and the supercooling degree can be significantly reduced with the increase of the EG content.The present work shows that the 10 wt.%EG content of form-stable composite PCM exhibits an optimal overall performance with a high thermal conductivity of 12.51 W/(m-K)(17.38 times higher than pure erythritol),a low supercooling degree of 19.5?(11? lower than that of pure erythritol),and a good cyclic stability after 140 cycles.Therefore,it is proposed in this study as a promising PCM for mid-temperature TES.