Visualized experiment on solid-liquid phase change heat transfer enhancement with multiple PCMs

doi:10.11949/j.issn.0438-1157.20180936

Abstract

Abstract:

Visualization experiments were carried out on the melting-solidification cycle process and heat transfer characteristics of the multiple phase change materials (multiple PCMs) using high-definition cameras and infrared thermal imaging technology. Three paraffins (RT65, RT42 and RT27) were used as multiple PCMs and filled into the TES container. The effect of PCM arrangement on thermal performance of the TES container was investigated. The dynamic evolution of solid-liquid interfaces was recorded by a high definition (HD) camera and the variation of temperature distribution was measured by an infrared camera. As the melting-solidification cyclic process was stabilized, the solid-liquid phase change behavior and thermal characteristics of the multiple-PCM TES container were obtained and compared with that of single-PCM TES container. The results show that the PCM with higher phase change temperature should be located near the heated wall. There exist multiple solid-liquid interfaces in multiple-PCM TES container, the paraffins in different PCM units can melt/solidify simultaneously. The uniformity of phase change rate is greatly improved by multiple PCMs, which increases the average phase change rate. The phase change fraction of multiple-PCM TES container is 40% higher than that of single-PCM TES container. Although the sensible heat storage capacity of multiple-PCM TES container is a little lower than that of single-PCM TES container, the variation rate of temperature is reduced, which enables the TES container work more stable. The latent heat storage capacity of TES container is significantly increased by the utilization of multiple PCMs. As a result, the total heat storage capacity of multiple-PCM TES container is 34.6% higher than that of single-PCM TES container.

Key words: multiple PCMs, thermal energy storage, phase interface, temperature distribution, visualization

摘要：

采用高清相机和红外热像技术，对组合相变材料融化-凝固循环过程与传热特性开展了可视化实验研究。以填充三种石蜡的相变蓄热腔体为研究对象，追踪了腔体内固液相界面的动态演化过程和温度分布的变化规律。在此基础上，考察了相变材料布置顺序对蓄热腔体热性能的影响，分析了组合相变材料蓄热腔体的相变行为及强化传热特性。结果表明，相变温度较高的相变材料应靠近加热壁面布置；组合相变材料蓄热腔体存在多个固液相界面现象，不同相变材料可同时融化/凝固；与单一相变材料相比，组合相变材料的应用改善了蓄热腔体各单元相变速率的均匀性，提高了平均相变速率；组合相变材料虽然降低了蓄热腔体的显热蓄热量，但减小了温度变化速率，增强了系统的稳定性，并显著增加了潜热蓄热量，有效提高了相变蓄热腔体的总蓄热量。

关键词: 组合相变材料, 蓄热, 相界面, 温度分布, 可视化

CLC Number:

TK 124

Huiru WANG, Zhenyu LIU, Yuanpeng YAO, Huiying WU. Visualized experiment on solid-liquid phase change heat transfer enhancement with multiple PCMs[J]. CIESC Journal, 2019, 70(4): 1263-1271.

王慧儒, 刘振宇, 姚元鹏, 吴慧英. 组合相变材料强化固液相变传热可视化实验[J]. 化工学报, 2019, 70(4): 1263-1271.

Figures/Tables 12

Fig.1 DSC curves of paraffins

Table 1 Thermophysical properties of paraffins

热物性参数	RT65	RT42	RT27
相变温度T _m/℃	63.2	43.4	28.8
潜热h _sf /(kJ·kg^-1)	172.0	148.2	154.3
比热容c_p /(kJ·kg^-1·K^-1)
固体	2.90	3.02	3.44
液体	2.50	2.33	2.53
密度ρ /(kg?m^-3)
固体	870	880	870
液体	760	760	740
热导率λ/(W?m^-1?K^-1)
固体	0.23	0.24	0.23
液体	0.17	0.17	0.16

Fig.2 Schematic of visualized experimental system

Table 2 Arrangement of paraffins for single-PCM and multiple-PCM TES containers

编号	单一/组合相变材料	PCM 1^#	PCM 2^#	PCM 3^#
1^#	RT27	RT27	RT27	RT27
2^#	RT42	RT42	RT42	RT42
3^#	RT65	RT65	RT65	RT65
4^#	RT65–RT42–RT27	RT65	RT42	RT27
5^#	RT65–RT27–RT42	RT65	RT27	RT42
6^#	RT42–RT65–RT27	RT42	RT65	RT27
7^#	RT42–RT27–RT65	RT42	RT27	RT65
8^#	RT27–RT42–RT65	RT27	RT42	RT65
9^#	RT27–RT65–RT42	RT27	RT65	RT42

Fig.3 Solid-liquid interfaces for different arrangements of paraffins in single-PCM and multiple-PCM TES containers

Fig.4 Phase change fraction for different single PCM and multiple PCMs during melting-solidification process

Fig.5 Evolution of solid-liquid interfaces for different TES containers

Fig.6 Comparison of temperature measured between infrared camera and thermocouple

Fig.7 Variation of temperature distribution for different TES containers

Fig.8 Comparison of liquid fraction in different PCM units between single-PCM and multiple-PCM TES containers

Fig.9 Comparison of average liquid fraction between single-PCM and multiple-PCM TES containers

Fig.10 Comparison of heat storage capacity between single-PCM and multiple-PCM TES containers

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