石蜡与石蜡/膨胀石墨熔化性能的实验研究

doi:10.11949/0438-1157.20191527

摘要/Abstract

摘要：

为改善相变储能过程中石蜡(PA)的熔化性能，向PA中添加少量膨胀石墨(EG)制备了4种配比的石蜡/膨胀石墨复合相变材料(PA-EG)。通过热物性分析筛选出合适配比的PA-EG，并对其和PA在水平管壳式相变储能单元中的熔化过程进行了实验研究。根据相变材料的温度场变化以及加权法计算得到的熔化分数变化，对比分析了添加EG前后PA的熔化性能，并探究了加热温度对相变材料熔化性能的影响。结果表明，PA-EG3的热导率比PA高了7倍，且两者的相变温度和潜热相差不大。PA-EG3熔化过程中的自然对流效应弱于PA，但是较高的热导率能够显著改善相变储能单元中下部的熔化，使得其整体熔化速度快于PA。当加热温度为80℃时，PA-EG3的熔化过程比PA缩短了78.16%。此外，降低加热温度会使PA和PA-EG3的完全熔化时间都显著增加，但相同条件下PA-EG3的增加幅度更小。

关键词: 相变, 复合材料, 膨胀石墨, 水平管壳式, 加权法, 传热, 熔化性能

Abstract:

To improve the melting performance of paraffin (PA) during the phase change energy storage process, a small amount of expanded graphite (EG) was added to the PA to prepare four kinds of paraffin/expanded graphite composite phase change materials (PA-EG). The PA-EG with suitable proportion was screened out by thermophysics analysis, with melting process of PA-EG and PA in the horizontal shell and tube latent heat thermal energy storage unit being experimentally studied. Based on the changes in the temperature field of the phase change material and the weighted melting fractions calculated, the melting performance between PA and PA-EG was compared. Also, the effect of the heating temperature on the melting performance was explored. The results indicated that the thermal conductivity of PA-EG3 was 7 times higher than that of PA, while the phase transition temperature and latent heat remained relatively identical. The natural convection effect of PA-EG3 during melting was weaker than that of PA. However, higher thermal conductivity resulted from added EG could significantly improve the melting of middle and lower parts in the latent heat thermal energy storage unit, making its overall melting rate higher than that of pure PA. When the heating temperature was 80℃, the melting process of PA-EG3 is 78.16% shorter than that of PA. In addition, reduced heating temperature can significantly increase the complete melting time of PA and PA-EG3, with smaller increment for PA-EG3 under the same condition.

Key words: phase change, composites, expanded graphite, horizontal shell and tube, weighting method, heat transfer, melting performance

中图分类号:

TK 02

刘正浩, 张小松, 王昌领, 张牧星. 石蜡与石蜡/膨胀石墨熔化性能的实验研究[J]. 化工学报, 2020, 71(7): 3362-3371.

Zhenghao LIU, Xiaosong ZHANG, Changling WANG, Muxing ZHANG. Experimental study on melting performance of paraffin and paraffin/expanded graphite[J]. CIESC Journal, 2020, 71(7): 3362-3371.

图/表 11

图1 相变材料熔化性能测试台

Fig.1 Melting performance test bench for phase change materials

图2 相变储能单元及温度测点布置

Fig.2 Latent heat thermal energy storage unit and temperature measurement point arrangement

图3 相变储能单元控制区域划分

Fig.3 Control area division of latent heat thermal energy storage unit

图4 4种PA-EG在70℃下的形貌

Fig.4 Morphology of four PA-EG at 70℃

图5 PA和PA-EG的热导率

Fig.5 Thermal conductivity of PA and PA-EG

图6 PA和PA-EG3的DSC曲线

Fig.6 DSC curves of PA and PA-EG3

图7 两种相变材料熔化过程中最外层测点(y=3)的温度变化

Fig.7 Temperature variation of the outermost measurement point (y = 3) during the melting of two phase change materials

图8 两种相变材料熔化过程中3方向测点的温度变化

Fig.8 Temperature variation in 3 direction during the melting of two phase change materials

图9 两种相变材料的熔化分数随时间变化

Fig.9 Melting fractions of two phase change materials over time

图10 PA的15个测点温度随时间变化(51~58 min)

Fig.10 Temperature variation of 15 measurement points of PA (51—58 min)

图11 两种相变材料在不同加热温度下的熔化分数随时间变化

Fig.11 Melting fraction over time of two phase change materials at different heating temperatures

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