Experimental study on melting performance of paraffin and paraffin/expanded graphite

doi:10.11949/0438-1157.20191527

Abstract

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

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

CLC Number:

TK 02

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.

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.

Figures/Tables 11

Fig.1 Melting performance test bench for phase change materials

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

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

Fig.4 Morphology of four PA-EG at 70℃

Fig.5 Thermal conductivity of PA and PA-EG

Fig.6 DSC curves of PA and PA-EG3

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

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

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

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

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

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