基于T-history法的脂肪酸相变材料的凝固-熔化动力学模型及关键参数

doi:10.19799/j.cnki.2095-4239.2024.0172

摘要/Abstract

摘要：

相变材料的熔化、结晶特性对相变储能具有重要意义，现有相变模型设定相分数与温度区间呈线性关系，未能考虑温度变化速率对相变过程的影响，因而在有关应用中的预测准确率较低。为研究温度与温度变化速率共同作用下的两相转化规律，对相变过程进行了理论分析，以相分数作为关键参数，通过固相和液相的PCM组分之间的可逆反应建立凝固-熔化动力学模型。设定Avrami方程作为模型中的反应函数，以Arrhenius方程作为模型中的速率函数。选用建筑领域常用的脂肪酸类相变材料正癸酸、月桂酸、辛酸作为实验材料，采用T-history法，通过等温结晶实验对Avrami方程进行拟合验证。经过验证证实Avrami方程与等温结晶实验所获得数据之间呈现出高度一致性与可靠性之后，通过非等温实验测试获得相变材料在不同温度与温度变化速率下的热力学信息，结合热分析动力学方法，对模型中的关键动力学参数研究测定。研究结果表明：活化能与常数因子变化趋势一致且存在互补效应，不同相变材料的活化能与常数因子大小不同，随相变过程进行，变化情况不同。反应级数随着温度变化速率的增大而减小，且凝固过程的反应级数普遍大于熔化过程。

关键词: Avrami模型, 相变动力学模型, T-history法, 动力学参数

Abstract:

Existing phase transition models artificially set the phase fraction to be linearly related to the temperature interval, failing to consider the influence of the temperature change rate on the phase transition process and resulting in a low prediction accuracy. In this study, to investigate the two-phase transformation law under the joint effect of temperature and the temperature change rate, a theoretical analysis of the phase change process is conducted and a solidification-melting kinetic model is established through the reversible reaction between the PCM components in the solid and liquid phases using the phase fraction as the key parameter. The Avrami equation was set as the reaction function in the model, and the Arrhenius equation was used as the rate function. Fatty acid phase change materials commonly used in the construction field (i.e., n-decanoic acid, lauric acid, and octanoic acid) were selected as experimental materials, and the Avrami equation was fitted and verified via isothermal crystallization experiments using the T-history method. After verifying that the Avrami equation shows a high degree of consistency and reliability with the data obtained from isothermal crystallization experiments, the thermodynamic characteristics of the phase-change materials at different temperatures and rates of temperature change were evaluated using non-isothermal experiments. The key kinetic parameters in the model were investigated and obtained in conjunction with the kinetic thermal analysis method. The results show that the activation energy and constant factor change via the same trend and exhibit a complementary relationship. Moreover, the activation energy and constant factor differ between different phase-change materials, and these changes vary depending on the phase transition process. The number of reaction levels decreases with increasing temperature change rate, and the number of reaction levels during the solidification process is generally larger than that during the melting process.

Key words: Avrami model, phase transition kinetic model, T-history method, kinetic parameters

中图分类号:

TK 02

刘思麟, 曹晓玲, 张沛璐, 冷子瑜. 基于T-history法的脂肪酸相变材料的凝固-熔化动力学模型及关键参数[J]. 储能科学与技术, 2024, 13(8): 2634-2648.

Silin LIU, Xiaoling CAO, Peilu ZHANG, Ziyu LENG. Determination of the kinetic parameters of fatty acid phase-change materials based on the T-history method[J]. Energy Storage Science and Technology, 2024, 13(8): 2634-2648.

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材料	温度变化速率/(℃/min)	熔化温度区间/℃	凝固温度区间/℃
正癸酸	熔化0.4/凝固1.5	27.505~31.679	30.365~24.038
	熔化0.6/凝固1.7	27.709~32.031	30.358~23.502
	熔化0.8/凝固1.9	27.934~32.513	30.292~22.898
	熔化1.0/凝固2.1	28.132~33.032	30.139~22.369
	熔化1.2/凝固2.3	28.328~33.705	29.946~21.764

月桂酸	熔化0.4/凝固1.5	40.944~46.548	42.585~33.917
	熔化0.6/凝固1.7	41.063~47.244	42.320~32.742
	熔化0.8/凝固1.9	41.127~48.013	42.102~31.485
	熔化1.0/凝固2.1	41.226~48.561	41.972~30.316
	熔化1.2/凝固2.3	41.260~49.386	41.711~29.231

辛酸	熔化0.4/凝固1.5	11.602~16.114	13.536~6.932
	熔化0.6/凝固1.7	11.972~16.613	13.351~6.293
	熔化0.8/凝固1.9	12.051~17.124	13.183~5.410
	熔化1.0/凝固2.1	12.231~17.647	13.092~4.842
	熔化1.2/凝固2.3	12.313~18.151	12.931~4.273

材料	熔化相变焓/(J/g)	凝固相变焓/(J/g)
正癸酸	158.123	206.923
月桂酸	202.849	221.585
辛酸	140.688	172.492