Abstract:

In this paper, a porous material composite water-based magnetic multi-walled carbon nanotubes (MWCNT) is used to enhance the solidification/melting phase transition process. The magnetic modification of MWCNT was carried out by coating Fe₃O₄ on the sidewall of MWCNT, and the synergistic effect of the porous material properties and the solidification/melting properties of the water-based MWCNT phase change working fluid under the influence of a magnetic field was investigated experimentally. The results show that the thermal cycle time of the composite phase change materials with the addition of porous materials such as expanded graphite, nickel metal foam and copper metal foam were reduced by 30.9%, 15.6% and 36.9% respectively compared to pure water. The storage/release capacity of phase change materials increased with the increase of porosity and the decrease of pore density of copper metal foam. Under the action of 75 mT magnetic field, the water-based magnetic MWCNT with a concentration of 0.08% (mass) composite copper metal foam with the porosity of 95% and a pore density of 5 PPI has the highest cold storage/release capacity and average rate compared with other specifications of copper metal foam. Compared with pure water, the thermal cycling time decreased by 38.9%, the average rate increased by 50.3%, and the supercooling decreased by 74.4%. However, the storage/release capacity only decreased by 4.7% and 4.9%.

Key words: solidification/melting, cold storage/release, nanomaterials, copper metal foam, magnetic field, heat transfer, phase change

摘要：

采用多孔材料复合水基磁性多壁碳纳米管(multi-walled carbon nanotube， MWCNT)强化凝固/融化相变过程。将Fe₃O₄包覆于MWCNT侧壁对MWCNT进行磁化改性，并实验研究了多孔材料特性与磁场作用下水基磁性MWCNT相变工质凝固/融化特性的协同效应。结果表明，与纯水相比，添加膨胀石墨、泡沫镍、泡沫铜等多孔材料使相变材料的热循环时间分别缩短了30.9%、15.6%、36.9%。相变材料储/释冷量随泡沫铜孔隙率的增大、孔密度的减小而上升。在75 mT磁场作用下，与其他规格的泡沫铜相比，复合孔隙率95%，孔密度5 PPI的泡沫铜使浓度为0.08%(质量)的水基磁性MWCNT相变工质具有最高的储/释冷量和平均速率。与纯水相比，过冷度降低了74.4%，热循环时间缩短了38.9%，平均速率升高了50.3%，储/释冷量却仅降低4.7%和4.9%。

关键词: 凝固/融化, 蓄/释冷, 纳米材料, 泡沫铜, 磁场, 传热, 相变