Preparation And Thermal-physical Properties Of Erythritol Based Composite Phase Change Materials

The improvement of efficient energy storage and release technology has become the core technology of priority development around the world since the increasing serious issues of energy shortage and environmental problem caused by the fossil fuel energy supply system.Latent heat thermal energy storage technology,which using latent heat absorbed or released during phase transition of phase change materials to achieve energy storage,conversion and utilization,has become an ideal choice for utilizing low-grade heat sources such as solar energy and industrial waste heat due to its features of low cost,high energy storage density and excellent stability.As an excellent phase change material,erythritol has large latent heat and suitable phase transition temperature,especially suitable for industrial waste heat recovery and domestic hot water production.However,its serious supercooling and unmatched heat release efficiency limit its large-scale application.In view of this,this paper takes erythritol as the object and aims to improve its thermal-physical properties.A series of erythritol-based shape-stabilized composite phase change materials were prepared by hydrothermal and impregnation method.And the effects of carrier,nucleating agent and thickening agents on the supercooling and heat release efficiency of erythritol were investigated.Erythritol/reduced graphene aerogel(ET/HGA)composite phase change materials were prepared by hydrothermal method using erythritol as phase change material and graphene oxide as carrier precursor.The effects of nucleating agent and thickening agents on the thermal-physical properties of erythritol were studied.The results showed that the maximum loading rate of erythritol is 86.40% and the supercooling of ET/HGA2.0 decreased from 85.5 ℃ to 63.3 ℃,the heat release efficiency increased from 64.1% to 71.3% compared with pure ET due to the shape-stability and heterogeneous nucleation of HGA.The addition of xylitol(XT)could not only alleviate the supercooling of ET/HGA composite,but also arise the cold-crystallization when the addition amount was 20.0 wt%.Carboxymethyl cellulose(CMC)could effectively inhibit the supercooling of ET/HGA.And the supercooling trend of ET/HGA decreased first and then increased with the increase of CMC content,the minimum supercooling 6.8 ℃ and the highest heat release efficiency 97.0% when adding 2.0 wt% CMC.In order to further explore the influence of thickening agents for supercooling suppression of phase change materials,the effect of hydroxyethyl cellulose(HEC)and guar gum(GG)on supercooling degree and heat release efficiency of ET/HGA composies were studied.The results showed that GG had no obvious effect on the supercooling suppression of ET/HGA,and HEC also showed similar trend to that of CMC,which was decreased first and then increased,but the effect was significantly weaker than that of CMC.Meanwhile,CMC was applied to XT/HGA and PEG6000/HGA composite.The effect of CMC on supercooling supperssion of XT and PEG6000 was analyzed and the results showed that CMC could not improve the supercooling properties of XT and PEG6000.Combined with thermal infrared images and T-t curves,CMC might be suitable for phase change materials with difficult nucleation but fast crystallization rate.ET/rGA composite phase change materials were prepared by impregnation method using reduced graphene aerogel(rGA)which was prepared by self-assembly graphene oxide aqueous solution with ascorbic acid as reducing agent.The preparation process was optimized and the effects of rGA at different reduction temperature on the supercooling characteristics and cold-crystallization of ET were investigated.The results showed that the optimum preparation conditions were GO concentration 4 mg/mL,reduction time 5 h and one-time impregnation.The loading rate of erythritol in ET/rGA composites was over 92% and the supercooling degree of ET was decreased by about 20 ℃ with the introduction of rGA.Meanwhile,the supercooling degree decreased and the heat release efficiency increased gradually with the increase of reduction temperature of rGA.When adding 2.0 wt% CMC as thickening agent,compared with the thermal-physical properties of ET/HGA2.0-C2.0 and ET/rGA-C2.0 composite phase change materials which were respectively prepared by hydrothermal and impregnation method,the latent heat of fusion,supercooling degree and heat release ability were 297.0 J/g and 300.2 J/g,6.8 ℃ and 8.5 ℃,97.0% and 96.7%,respectively,which further illustrated that CMC had a specific inhibition effect on the supercooling of erythritol.At the same time,they also had excellent thermal cycling stability and reliability after 100 thermal cycles.To sum up,erythritol based composite phase change materials were prepared through both hydrothermal method and impregnation method,the thickener CMC could not only improve the thermal conductivity of ET,reduce the supercooling degree and improve the heat release efficiency,but also has the specific effect on inhibiting the supercooling of ET.Therefore,in order to verify the relationship between the thickening effects of thickeners and supercooling suppression,it can be applied to suppress the supercooling of phase change materials with poor nucleation and fast crystal growth rate,such as d-dulcitol and disodium hydrogen phosphate dodecahydrate.At the same time,the pore structure and interface effect of the confined carrier and the regularity of phase change behavior of phase change materials still need to be further explored and verified.