Abstract In order to explore a graphene-containing nanofluid with good dispersion stability as the working fluid for a low-temperature direct absorption solar collector (DASC), firstly, two kinds of functionalized graphene, hydroxylated graphene (GOH) and carboxylated graphene (GCOOH), were dispersed into a mixture of ethylene glycol (EG) and water (1:1 mass ratio), at the same loadings. It is found that, although the obtained GOH nanofluid exhibits a slight lower zeta potential than the GCOOH one, its optical absorption property is obviously higher. Consequently, GOH was employed to prepare the EG-water based nanofluids at different loadings, followed by the investigations on their optical absorption and thermophysical properties, photo-thermal conversion performance, and dispersion stability. It is shown that, at a loading as low as 0.007 wt%, the transmittance of the corresponding GOH/water-EG nanofluid is reduced to zero, and its extinction coefficient is 100 times higher than that of the base fluid. Under the illumination of 1000 W/m2, the 0.007 wt% GOH/EG-water nanofluid can reach a high final temperature of 55 °C. More significantly, the zeta potential of the 0.007 wt% GOH/EG-water nanofluid increases with temperature and reaches 47.63 mV at 60 ℃, suggesting its good dispersion stability at the elevated temperatures. These good characteristics of the GOH/EG-water nanofluid make it a very promising working fluid for a low temperature DASC.

中文翻译：

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一种高度稳定的羟基化石墨烯/乙二醇-水纳米流体在低负载下具有优异的消光性能，用于直接吸收太阳能集热器

摘要 为了探索具有良好分散稳定性的含石墨烯纳米流体作为低温直接吸收太阳能集热器（DASC）的工作流体，首先，两种官能化石墨烯，羟基化石墨烯（GOH）和羧化石墨烯（GCOOH） , 以相同的负载量分散到乙二醇 (EG) 和水 (1:1 质量比) 的混合物中。结果表明，虽然得到的 GOH 纳米流体的 zeta 电位略低于 GCOOH，但其光吸收性能明显更高。因此，采用 GOH 制备了不同负载量的 EG-水基纳米流体，然后研究了它们的光吸收和热物理性质、光热转换性能和分散稳定性。结果表明，在低至 0.007 wt% 的负载量下，相应的GOH/水-EG纳米流体的透光率降为零，其消光系数比基液高100倍。在 1000 W/m2 的光照下，0.007 wt% GOH/EG-水纳米流体可以达到 55°C 的高最终温度。更重要的是，0.007 wt% GOH/EG-水纳米流体的zeta电位随温度升高，在60 ℃下达到47.63 mV，表明其在高温下具有良好的分散稳定性。GOH/EG-水纳米流体的这些良好特性使其成为非常有前途的低温 DASC 工作流体。007 wt% GOH/EG-水纳米流体可以达到55°C的高最终温度。更重要的是，0.007 wt% GOH/EG-水纳米流体的zeta电位随温度升高，在60 ℃下达到47.63 mV，表明其在高温下具有良好的分散稳定性。GOH/EG-水纳米流体的这些良好特性使其成为非常有前途的低温 DASC 工作流体。007 wt% GOH/EG-水纳米流体可以达到55°C的高最终温度。更重要的是，0.007 wt% GOH/EG-水纳米流体的zeta电位随温度升高，在60 ℃下达到47.63 mV，表明其在高温下具有良好的分散稳定性。GOH/EG-水纳米流体的这些良好特性使其成为非常有前途的低温 DASC 工作流体。