高导热膨胀石墨/棕榈酸定形复合相变材料的制备及储热性能研究

doi:10.11949/0438-1157.20190179

摘要/Abstract

摘要：

采用棕榈酸(palmitic acid, PA)作为相变材料，膨胀石墨(expanded graphite, EG)作为添加基质，通过“熔融共混-凝固定形”工艺制备了PA/EG定形复合相变材料以提高相变材料的综合性能。预测并制备了21种不同配比的定形复合相变材料，对其形貌结构和孔隙率进行了微观表征与理论分析，并在此基础上对样品进行了传热性能分析、热物性测试、热稳定性研究和储热性能分析。SEM形貌分析显示所使用工艺可使棕榈酸能较好地被吸附于膨胀石墨的孔隙结构并使之均匀分布；DSC测试结果表明定形复合相变材料[70%(质量) PA]的焓值为193.01 J/g，纯PA的焓值为275.35 J/g，对应于熔点分别为61.08℃和59.53℃。EG的添加，可有效提高相变材料的热导率。当样品密度为900 kg/m³，EG含量为30%(质量)时，定形复合相变材料的热导率为14.09 W/(m·K)，相比于纯PA[0.162 W/(m·K)]提高约87倍；对制备的样品进行50次循环稳定性实验，EG含量为24%(质量)和30%(质量)的样品形态均未出现明显变化，表现出良好的充放热循环稳定性。

关键词: 棕榈酸, 膨胀石墨, 定形, 相变材料, 制备, 储热性能

Abstract:

A kind of composite phase change materials (PCMs) was prepared by the process of “melting blend - solidification and form-stable” to improve the comprehensive performance of PCMs. Palmitic acid (PA) is used as PCM and expanded graphite (EG) is used for the supporting material. Twenty-one kinds of form-stable composite PCMs were prepared with different contents of EG. The morphologies and structures were characterized microscopically by SEM. On this basis, heat transfer performance analysis, thermophysical test, thermal stability test and heat storage performance analysis were conducted. SEM morphological characterization showed that PA could be absorbed into the pores of EG and the distribution was uniform. DSC test results revealed that the melting enthalpy of PCMs is 193.01 J/g with the 70%(mass) PA corresponding to the melting point of 61.08℃. The melting enthalpy of pure PA is 275.35 J/g corresponding to the melting point of 59.53℃. The thermal conductivity of the PCMs is significantly improved by the addition of EG. When the sample density was 900 kg/m³ and the content of EG was 30%(mass), the thermal conductivity of the composite PCM is 14.09 W/(m·K), which is about 87 times higher than that of pure PA. Cycle stability tests were carried out, the results suggest the samples with 24% and 30% EG content have no any change in shape, and therefore show excellent cycle stability in repeating charging and discharging processes.

Key words: palmitic acid, expanded graphite, form-stable, phase change materials (PCMs), preparation, thermal energy storage performance

中图分类号:

TK 124

吴韶飞, 闫霆, 蒯子函, 潘卫国. 高导热膨胀石墨/棕榈酸定形复合相变材料的制备及储热性能研究[J]. 化工学报, 2019, 70(9): 3553-3564.

Shaofei WU, Ting YAN, Zihan KUAI, Weiguo PAN. Preparation and thermal energy storage properties of high heat conduction expanded graphite/palmitic acid form-stable phase change materials[J]. CIESC Journal, 2019, 70(9): 3553-3564.

图/表 15

图1 PA/EG定形复合相变储热材料样品制备步骤

Fig.1 Preparation procedure of PA/EG form-stable composite PCMs sample

图2 PA/EG定形复合相变储热材料样品

Fig.2 PA/EG form-stable composite PCMs sample

图3 PA/EG定形复合相变储热材料样品密度随孔隙率的关系曲线

Fig.3 Change of PA/EG form-stable composite PCMs density with porosity

图4 PA/EG定形复合相变储热材料不同配比的样品实物图

Fig.4 PA/EG form-stable composite PCM samples with different proportions

表1 不同质量分数的EG和不同密度的PA/EG定形复合相变储热材料样品配比

Table1 PA/EG form-stable composite PCMs sample with different mass fractions of EG and different densities

方块密度/(kg/m³)	EG/%(mass)	质量/g	密度/(kg/m³)	样品序号
600	6	38.977	609	S1
	12	50.940	596	S2
	18	38.076	595	S3
	24	38.339	599	S4
	30	38.001	594	S5
700	6	44.530	696	S6
	12	44.539	696	S7
	18	44.596	697	S8
	24	44.679	698	S9
	30	44.730	699	S10
800	6	50.940	796	S11
	12	50.840	794	S12
	18	51.095	798	S13
	24	51.098	798	S14
	30	51.138	799	S15
900	6	—	—	—
	12	57.485	898	S16
	18	57.429	897	S17
	24	57.487	898	S18
	30	57.252	895	S19
1000	6	—	—	—
	12	—	—	—
	18	—	—	—
	24	63.847	998	S20
	30	63.620	994	S21

图5 膨胀石墨和复合相变材料的SEM图

Fig.5 SEM image of EG and composite PCMs

图6 纯PA与五种不同配比的PA/EG定形相变材料样品的DSC曲线

Fig.6 DSC curves of pure PA and five different proportions of PA/EG form-stable composite PCM samples

图7 PA/EG复合相变材料样品的相变潜热随EG质量分数的预测和实际曲线

Fig.7 Prediction and experimental curve of latent heat of PA/EG composite PCMs samples with EG mass fraction

图8 PA/EG定形相变材料样品的过冷度随EG含量的变化

Fig.8 Relation curve of supercooling degree of PA/EG form-stable PCMs with content of EG

图9 EG吸附PA形成复合相变材料的微观结构

Fig.9 Microstructure of PA/EG composite PCMs

图10 EG含量为30%时PA/EG定形复合材料样品水平和垂直方向的热导率随样品密度的变化

Fig.10 Changes in horizontal and vertical thermal conductivity of PA/EG form-stable composite samples with sample density when content of EG is 30%(mass)

图11 有效热导率随样品密度的变化

Fig.11 Curve of thermal conductivity with sample density

图12 热导率随循环次数的变化曲线

Fig.12 Relation curve of effective thermal conductivity change with cycle times

图13 样品质量变化随充放热循环次数的关系曲线

Fig.13 Relation curve of sample mass change with cycle times

图14 充/放热循环过程中样品形态的变化

Fig.14 Changes of sample morphology during charging/discharging process

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