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| Non-isothermal crystallization of aqueous graphene oxide suspensions |
| WANG Xiao1,YAO Xiao-li1,HOU Jian-feng1,FAN Li-wu1,XU Xu2,YU Zi-tao1,HU Ya-cai1 |
| 1. Institute of Thermal Science and Power Systems,Zhejiang University,Hangzhou 310027,China；2. College of Metrological and Measurement Engineering,China Jiliang University,Hangzhou 310018,China |
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Abstract The thermal conductivity of phase change materials can be efficiently increased by adding graphene nanoadditives to form suspensions. The presence of the graphene nanoadditives is expected to have considerable influence on the solid-liquid phase change characteristics of the suspensions. The aqueous suspensions in the presence of graphene oxide nanosheets at dilute concentrations were characterized via the non-isothermal crystallization method on a differential scanning calorimeter. The dependence of the supercooling degree of the suspensions on the concentration (up to mass fraction of 1%) and the cooling rate was analyzed. Results show that the supercooling degree is lower than that of pure water due to the presence of the graphene oxide nanosheets and decreases gradually with increasing the mass fraction. The lowering of the supercooling degree was nearly 5 ℃ at the highest mass fraction of 1%. In addition, the supercooling degree was shown to rise slightly with increasing the cooling rate, whereas the relative variation of the supercooling degree with respect to mass fraction was unaffected. The utilization of aqueous graphene oxide suspensions as cold storage media can lower the supercooling degree,whereas the non-isothermal crystallization processes are unable to be shortened．
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Published: 04 August 2014
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氧化石墨烯水悬浮液的非等温结晶过程
采用添加石墨烯纳米材料形成悬浮液的方法可以有效地提高相变储能材料的导热系数,石墨烯纳米材料的存在将对悬浮液的固液相变行为产生可观的影响. 利用差示扫描量热仪对低质量分数的氧化石墨烯水悬浮液进行非等温结晶实验观测,对比分析不同质量分数（最高为1%）的悬浮液在不同降温速率情况下过冷度的变化规律. 实验结果表明,由于氧化石墨烯的存在,悬浮液的过冷度较纯水有所降低. 随着质量分数的提高,悬浮液的过冷度呈逐步下降的趋势,当最高质量分数为1%时,悬浮液的过冷度较纯水下降了近5 ℃. 悬浮液的过冷度随着降温速率的增大会略微升高,但降温速率对过冷度随悬浮液质量分数的相对变化没有影响. 采用氧化石墨烯水悬浮液作为蓄冷工质能够有效地降低水的过冷度,但对整个非等温结晶过程未体现出加速的效果．
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