该文实验研究了磁场作用下水基磁性碳纳米管（MWCNT-Fe3O4）流体光热转换特性。采用改进化学共沉淀法合成MWCNT-Fe3O4复合纳米磁性材料,制备了浓度为0.001%~0.200%（质量分数）的磁流体。此外,研究了磁场强度及方向对磁性流体光热转换特性的影响。结果表明：在低浓度范围内光热转换效率随浓度增加而增加,并在0.01%时获得比纯水提高了30%的光热转换效率。高浓度时由于透光率降低使得光热转换效率有所下降。磁性MWCNT材料在外加磁场作用下将会呈现与磁场方向一致的定向排列现象。垂直磁场作用下,MWCNT排列方向与温度梯度方向一致,充分利用其轴向超高导热系数使流体中的温度分布更均匀,光热转换效率提高。水平磁场作用下,MWCNT排列方向与温度梯度方向垂直,抑制了流体中的热量传递,光热转换效率下降。
Abstract
In this paper, the photothermal conversion characteristics of water-based magnetic Multiwall Carbon Nanotube （MWCNT-Fe3O4) fluids were experimentally studied. MWCNT-Fe3O4 nanocomposite were synthesized by improved chemical co-precipitation method. The photothermal conversion experiments were carried out on the magnetic fluids with mass concentrations of 0.001%, 0.005%, 0.010%, 0.050, 0.100% and 0.200%, respectively. In addition, the effect of magnetic field intensity and direction on the photothermal conversion performance of magnetic fluid were investigated. The results show that the photothermal conversion efficiency increases with the increased concentration in the lower concentration range, and the 30% higher photothermal conversion efficiency than that of pure water is obtained at concentration of 0.01%. However, the photothermal conversion efficiency decreases due to the decreased light transmittance at the higher concentration. In addition, magnetic MWCNT will be oriented distribution under the action of magnetic field. The photothermal conversion efficiency is improved under the action of vertical magnetic field because its ultra-high axial thermal conductivity is consistent with temperature gradient direction to make the even temperature distribution in the fluid. The MWCNT arrangement direction is perpendicular to the temperature gradient direction, which suppresses the heat transfer in the fluid under the action of horizontal magnetic field. As a result, the photothermal conversion efficiency is reduced.
关键词
磁流体 /
太阳能 /
碳纳米管 /
光热转换 /
磁场
Key words
magnetic fluids /
solar energy /
carbon nanotubes /
photo-thermal conversion /
magnetic field
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基金
国家自然科学基金项目（51906013）; 北京建筑大学金字塔人才培养工程建大英才项目（JDYC20200316）
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