A new approach to determine the degree of subcooling in phase-change paraffin emulsion: equilibrium volumetry

doi:10.11949/0438-1157.20190293

Abstract

Abstract:

Paraffin phase change emulsion is a new type of functional fluid that integrates heat storage and heat transfer, and has broad application prospects. However, the application of phase-change paraffin emulsion suffers from subcooling phenomenon, which weakens its ability to store and transfer heat remarkably. The degree of subcooling in phase-change paraffin emulsion is conventionally determined by differential scanning calorimetry (DSC), the result of which is dependent on the heating / cooling rate. As the heating / cooling rate increases, the degree of subcooling is higher. Here an equilibrium volumetric method was presented to determine the degree of subcooling in phase-change paraffin emulsion by measuring its specific volume at different temperatures. The specific volume obtained was plotted against the temperature to identify the phase transition temperature of paraffin during heating / cooling process, then the degree of subcooling was deduced from the phase transition temperatures obtained. The results showed that the degree of subcooling in phase-change paraffin emulsion can be measured accurately using the equilibrium volumetric method presented in this work. The results also revealed the mechanism of subcooling in phase-change paraffin emulsion from the point of view of specific volume change.

Key words: volumetric method, DSC, subcooling, paraffin, phase transition

摘要：

石蜡相变乳液是集储热与传热于一体的新型功能流体，具有广阔的应用前景。但石蜡相变乳液在降温时会出现过冷现象，极大降低了其储热与传热的性能。采用差示扫描量热法（DSC）测量石蜡相变乳液的过冷度受到升/降温速率的影响，且升/降温速率越大，测得过冷度越大。提出一种测量石蜡相变乳液过冷度的方法——平衡态比容法。该方法通过测量石蜡相变乳液在不同温度下的比容，以确定乳液中石蜡粒子在升/降温过程中的相变温度，并进一步求解石蜡相变乳液的过冷度。实验结果表明，本研究提出的平衡态比容法能准确测量石蜡相变乳液的过冷度，并从比容变化的角度揭示石蜡相变乳液过冷现象的机理。

关键词: 比容法, 差示扫描量热法, 过冷, 石蜡, 相变

CLC Number:

O 648.23

Lin CHEN, Yafei WU, Liming CHE. A new approach to determine the degree of subcooling in phase-change paraffin emulsion: equilibrium volumetry[J]. CIESC Journal, 2019, 70(9): 3370-3376.

陈琳, 武亚飞, 车黎明. 一种测量石蜡相变乳液过冷度的新方法：平衡态比容法[J]. 化工学报, 2019, 70(9): 3370-3376.

Figures/Tables 9

Fig.1 Equilibrium volumetric method apparatus

Fig.2 Preparation of phase-change paraffin emulsion

Fig.3 Particle size distribution of paraffin emulsion

Fig.4 DSC curves of bulk paraffin

Fig.5 Correlation between phase transition temperature of bulk paraffin and heating/cooling rate

Fig.6 DSC curves of paraffin emulsions with different particle sizes

Table 1 Degree of subcooling of paraffin emulsions with different particle sizes

平均粒径/nm	过冷度/℃
平均粒径/nm	5 K·min^-1	10 K·min^-1	15 K·min^-1	20 K·min^-1	0 K·min^-1
330	16.5	18.1	19.0	20.1	15.5
217	16.3	18.1	19.4	21.0	14.9
147	16.0	17.3	18.6	19.3	15.0

Fig.7 Volumetric evolution of paraffin emulsion during heating/cooling

Fig.8 Thermal expansion of paraffin emulsion with different particle sizes

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