熔融聚乙二醇滴入油池的颗粒凝固成形特性研究

doi:10.11949/0438-1157.20250429

摘要/Abstract

摘要：

直接接触式潜热储热通过相变材料与传热流体的直接接触，实现更高的储热密度与速率，但熔化过程需要一定时间形成对流换热通道。相变材料颗粒的形状和大小会影响通道的结构，从而影响储热性能。通过实验与数值模拟，研究了熔融聚乙二醇液滴滴入油池的颗粒凝固成形特性。利用高速相机和电子显微镜，分析了滴落高度、油池深度及液滴直径的影响。实验结果表明，超过临界滴落高度会导致液滴抛射并发生碰撞；油池深度与液滴直径显著影响液滴触底前的凝固程度，从而影响颗粒成形质量。通过半解析-半经验的计算方法，认为液滴触底时的凝固层厚度约为半径的7.67%时成形效果较好。提出用表面张力系数σ修正液滴形状的数值模型，当σ=0.1时，模拟结果与实验数据吻合良好。数值模拟揭示了液滴凝固过程中的非均匀性传热特征：顶部区域因回流扰动而冷却速率最快，侧部传热较弱。此外，液滴直径与传热流体温度对临界油池深度的影响呈非线性。

关键词: 直接接触, 相变, 液滴, 凝结, 成形, 数值模拟

Abstract:

In direct-contact latent heat storage systems, phase change material (PCM) directly contacts the heat transfer fluid (HTF), enabling higher storage density and rate. However, forming convective channels during melting takes time, and particle shape and size affect channel structure and heat storage performance. This study investigates the solidification of molten polyethylene glycol droplets falling into an oil pool through experiments and simulations. The effects of drop height, oil pool depth, and droplet diameter were analyzed using a high-speed camera and electron microscope. The results show that exceeding a critical falling height causes droplet splashing and collisions. Oil depth and droplet size significantly affect solidification before bottom contact, influencing particle formation. A semi-analytical and empirical model suggests optimal shaping occurs when the solid layer thickness is about 7.67% of the droplet radius. A surface tension correction model was proposed, and when σ = 0.1, simulation results matched experimental data well. Simulations also reveal non-uniform heat transfer: the top cools fastest due to backflow disturbance, while side heat transfer is weaker. Additionally, droplet diameter and fluid temperature exhibit nonlinear effects on the critical oil depth.

Key words: direct contact, phase change, droplet, condensation, shaping, numerical simulation

中图分类号:

TK 02

郑章靖, 杨清云, 闫室兴, 施宇辰, 徐阳. 熔融聚乙二醇滴入油池的颗粒凝固成形特性研究[J]. 化工学报, 2025, 76(12): 6302-6313.

Zhangjing ZHENG, Qingyun YANG, Shixing YAN, Yuchen SHI, Yang XU. Research on solidification characteristics of particles formed by dropping molten polyethylene glycol into oil pool[J]. CIESC Journal, 2025, 76(12): 6302-6313.

图/表 19

表1 PCM和HTF的热物理性质

Table 1 The thermophysical properties of PCM and HTF

物性参数	导热油	聚乙二醇4000
密度/(kg·m^-3)	857	1125
运动黏度/(mm²·s^-1)	270 (0℃)，29 (40℃)	8~11
热导率/(W·(m·K)^-1)	0.135	0.085
比热容/(kJ·(kg·K)^-1)	2.049	2.048
熔化温度/℃	—	46.93~62.75
凝固温度/℃	-12	34.21~42.8
潜热/(kJ·kg^-1)	—	117.32

图1 实验装置示意图

Fig.1 Schematic diagram of the experimental apparatus

图2 几何模型

Fig.2 Geometric model

图3 部分区域的网格划分示意图

Fig.3 Schematic diagram of grid division for some areas

图4 聚乙二醇液滴撞击油池表面的时间图像（z=10 cm）

Fig.4 The time graph of polyethylene glycol droplets hitting the surface of the oil pool (z=10 cm)

图5 聚乙二醇液滴撞击油池表面的时间图像（z=100 cm）

Fig.5 The time graph of polyethylene glycol droplets hitting the surface of the oil pool (z=100 cm)

图6 颗粒直径测量

Fig.6 Particle diameter measurement

图7 不同G值下的聚乙二醇固体颗粒图片（侧视图）

Fig.7 Solidified polyethylene glycol particle morphologies under different G values (side view)

图8 滴落高度z对球形程度G和颗粒直径d的影响

Fig.8 The influence of the drop height z on the sphericity degree G and the particle diameter d

图9 聚乙二醇颗粒接触油池底部的形状变化过程（侧视图）

Fig.9 The shape change process of polyethylene glycol particles in contact with the bottom of the oil pool (side view)

图10 不同油池深度下，三种弯头直径形成的固体颗粒形貌

Fig.10 Solidified particle morphologies formed under different oil pool depths and elbow diameters

图11 不同直径的聚乙二醇颗粒球形程度G随油池深度的变化

Fig.11 The sphericity degree G of polyethylene glycol particles of different diameters varies with the depth of the oil pool

表2 液滴临界凝固层厚度比计算结果

Table 2 Calculation results of the thickness ratio of the critical solidification layer of the droplet

液滴直径/mm

油池深度/cm

触底时间/

平均速度/(m

/

表2 液滴临界凝固层厚度比计算结果

Table 2 Calculation results of the thickness ratio of the critical solidification layer of the droplet

液滴直径/mm

油池深度/cm

触底时间/

平均速度/(m

/

临界凝固层厚度比

3.9

4.95

0.0424

0.0827

4.2

5.49

0.0455

0.0802

4.9

5.30

0.0528

0.0672

图12 不同表面张力系数液滴形状对比

Fig.12 Comparison of droplet shapes with different surface tension coefficients

图13 相变材料液滴在不同时刻的温度云图

Fig.13 Temperature contour maps of PCM droplet at various steps

图14 相变材料液滴在不同时刻的凝固程度云图

Fig.14 Solidification degree contours of PCM droplet at various times

图15 液滴沉降过程中速度场的分布

Fig.15 Velocity field distribution during droplet sedimentation

图16 临界油池深度与液滴直径的关系

Fig.16 The relationship between the critical oil pool depth and the droplet diameter

图17 临界油池深度与HTF温度的关系

Fig.17 The relationship between the critical oil pool depth and the HTF temperature

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