Vallejo Javier P, Żyła Gaweł, Fernández-Seara José, Lugo Luis
Departamento de Física Aplicada, Facultade de Ciencias, Universidade de Vigo, E-36310 Vigo, Spain.
Área de Máquinas e Motores Térmicos, Escola de Enxeñería Industrial, Universidade de Vigo, E-36310 Vigo, Spain.
Nanomaterials (Basel). 2019 Jan 24;9(2):146. doi: 10.3390/nano9020146.
Nanofluids, dispersions of nanosized solid particles in liquids, have been conceived as thermally-improved heat transfer fluids from their conception. More recently, they have also been considered as alternative working fluids to improve the performance of direct absorption solar thermal collectors, even at low nanoadditive concentrations. Carbon-based nanomaterials have been breaking ground in both applications as nanoadditives during the last decade due to their high thermal conductivities and the huge transformation of optical properties that their addition involves. In any application field, rheological behavior became a central concern because of its implications in the pumping power consumption. In this work, the rheological behavior of four different loaded dispersions (0.25, 0.50, 1.0, and 2.0 wt%) of six carbon-based nanomaterials (carbon black, two different phase content nanodiamonds, two different purity graphite/diamond mixtures, and sulfonic acid-functionalized graphene nanoplatelets) in ethylene glycol:water mixture 50:50 vol% have been analysed. For this purpose, a rotational rheometer with double cone geometry was employed, which included a special cover to avoid mass losses due to evaporation at elevated temperatures. The flow curves of the twenty-four nanofluids and the base fluid were obtained by varying the shear rate between 1 and 1000 s for seven different temperatures in the range from 283.15 to 353.15 K. The shear-thinning behaviors identified, as well as their dependences on carbon-based nanomaterial, concentration, and temperature, were analyzed. In addition, oscillatory tests were performed for samples with the clearest Non-Newtonian response, varying the deformation from 0.1 to 1000% with constant frequency and temperature. The dependence of the behaviors identified on the employed carbon-based nanomaterial was described.
纳米流体，即纳米级固体颗粒在液体中的分散体，自其诞生以来就被视为热性能得到改善的传热流体。最近，它们还被视为替代工作流体，用于提高直接吸收式太阳能集热器的性能，即使在纳米添加剂浓度较低的情况下也是如此。在过去十年中，碳基纳米材料因其高导热性以及添加后所涉及的光学性质的巨大转变，在这两种作为纳米添加剂的应用领域都取得了突破性进展。在任何应用领域，流变行为都因其对泵送功耗的影响而成为核心关注点。在这项工作中，分析了六种碳基纳米材料（炭黑、两种不同相含量的纳米金刚石、两种不同纯度的石墨/金刚石混合物以及磺酸功能化的石墨烯纳米片）在体积比为50:50的乙二醇:水混合物中的四种不同负载量分散体（0.25、0.50、1.0和2.0 wt%）的流变行为。为此，使用了具有双锥几何形状的旋转流变仪，该流变仪包括一个特殊的盖子，以避免在高温下因蒸发导致质量损失。通过在283.15至353.15 K范围内的七个不同温度下，将剪切速率在1至1000 s之间变化，获得了这二十四种纳米流体和基础流体的流动曲线。分析了所确定的剪切变稀行为及其对碳基纳米材料、浓度和温度的依赖性。此外，对具有最明显非牛顿响应的样品进行了振荡测试，在恒定频率和温度下将变形从0.1%变化到1000%。描述了所确定的行为对所使用的碳基纳米材料的依赖性。
