Supercooling suppression and crystallization behaviour of erythritol/ expanded graphite as form-stable phase change material

The serious supercooling of erythritol (ET) limits its application in the field of mid-temperature thermal energy storage (TES), especially in the recently developed form-stable phase change materials (PCMs). The primary purpose of this paper is to find out the factors to mitigate the supercooling of ET/expanded graphite (EG) formstable composite PCM and obtain the correlation among the morphology, kinetic parameters, and a supercooling degree in the non-isothermal crystallization process. Firstly, five types of supercooling relaxation agents (nanoAl2O3, nano-SiO2, CMC, urea, and citric acid) were added to prepare the ET/EG form-stable CPCMs. Among them, the ET/EG/nano-Al2O3 exhibited excellent form-stable ability, a high heat release ratio of 78.9%, and the lowest supercooling degree (?T) of 45.7 ?C. Based on the chosen ET/EG/nano-Al2O3 CPCM, the tablet pressures from 1 to 13 MPa were applied, obtaining lowest ?T decreased by 59.0% in 1 MPa. Moreover, the non-isothermal crystallization processes were discussed on the ET/EG/nano-Al2O3 with the Avrami equation modified by Jeziorny. ET tended to grow spherulites under the high cooling rate of 18 ?C/min with triggering as the JohnsonMehl-Avrami exponent n increased to 4.22. Meanwhile, the supercooling degree increased from 48.8 to 56 ?C with the cooling rate growing from 2 to 18 ?C/min. And the activity energy ?E of the ET/EG/nano-Al2O3 CPCM (7092.35 kJ/mol) was smaller than that of the ET/EG CPCM (8211.19 kJ/mol) because of the interaction between the heterogeneous nucleation effect and blocker effect of nano-Al2O3.

Automated summary

The study aims to mitigate the supercooling issue in erythritol/expanded graphite composite phase change materials, focusing on the correlation between morphology, kinetic parameters, and supercooling degree during non-isothermal crystallization. Various supercooling relaxation agents were tested to prepare the composite PCM, with nano-Al2O3 showing the best results. In addition, pressure and cooling rate were found to impact the supercooling degree and crystallization behavior of the composite PCM.