Experimental research and numerical simulation of the thermal performance of a tube-fin cold energy storage unit using water/modified expanded graphite as the phase change material
Jinxin Feng, Ziye Ling, Jiangchang Huang, Xiaoming Fang, Zhengguo Zhang
Abstract
In this study, experimental and numerical investigations were conducted on a tube-fin heat-exchanger latent-heat cold energy storage unit. The fin side of the heat exchanger was filled with water as the energy storage medium, and modified expanded graphite (MEG) was employed to improve the thermal characteristics of water. The water contact angle of the expanded graphite decreased from 106.31° to 0°, and the hydrophilicity and the absorption rate of water significantly improved after the modification. Moreover, the experimental analyses of the charge/discharge process showed that the cooling capacity of the system filled with 90 wt.% water/MEG was 80.8% of that of pure water, whereas its cooling time was only 69.7% of that of pure water. The average power increased by 15.9% compared with that of water. The system filled with 90 wt.% water/MEG completed two energy charging and discharging cycles, whereas the system filled with water completed only 1.5 cycles within 15000 s. Furthermore, the effects of the flow rate and inlet temperature of the heat transfer fluid on the charging process were explored. Finally, a numerical model was built and validated to investigate the phase change behavior and the effect of the structure size on the performance of the system. The heat-exchanger fin spacing had no significant effect on the cold energy storage unit, whereas the vertical spacing of the tube pass had the highest effect. It can be concluded that the heat exchanger combined with high-thermal-conductivity water/MEG exhibits better energy storage capacity and working power, showing a wide application prospect in the field of cold energy storage.