Abstract The application of spinel ferrite decorated graphene hybrids in heat transfer has been limited mostly due to their poor stability in water. This study reports a straightforward strategy to synthesis a cobalt ferrite/reduced graphene oxide (CoFe2O4/rGO) nanocomposite with high water dispersibility characteristics through the treatment of synthesized hybrid material with Gallic acid (GA) as a green agent at room temperature. A π-π interaction between graphene and the aromatic ring of GA results in a suspension with high stability. The structure of the nanocomposite was investigated in detail by FTIR, XRD, TGA, VSM, Raman spectroscopy, FESEM, and TEM. Also, UV–vis spectroscopy is used to examine the stability of the stability of the CoFe2O4/rGO in the base fluid. The highly stable aqueous nanofluids were subsequently prepared from the products. Thermo-physical analyses of nanofluids revealed that the thermal conductivity ratio of ferrofluid prepared by the obtained CoFe2O4/rGO with 0.9 wt.% load of nanoparticles at 60 °C is rose to 1.46. Besides, the convective heat transfer in laminar flow regime conditions which passes a circular tube under uniform heat flux was examined. The nanofluid with the highest load of nanoparticles (0.9 wt.%) shown the maximum enhancement in Nusselt number of 27.8 % at Reynolds number of 1713.

中文翻译：

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绿色合成高稳定性CoFe2O4/rGO纳米流体的热物理性质和传热特性的实验研究

摘要 尖晶石铁氧体修饰的石墨烯杂化物在传热中的应用受到限制，主要是由于它们在水中的稳定性差。该研究报告了一种直接的策略，通过在室温下用没食子酸 (GA) 作为绿色剂处理合成的杂化材料来合成具有高水分散性的钴铁氧体/还原氧化石墨烯 (CoFe2O4/rGO) 纳米复合材料。石墨烯与 GA 的芳环之间的 π-π 相互作用导致悬浮液具有高稳定性。通过FTIR、XRD、TGA、VSM、拉曼光谱、FESEM和TEM详细研究了纳米复合材料的结构。此外，UV-vis 光谱用于检查 CoFe2O4/rGO 在基液中的稳定性。随后由产物制备高度稳定的水性纳米流体。纳米流体的热物理分析表明，在 60°C 下，由所获得的 CoFe2O4/rGO 制备的铁磁流体的热导率比为 0.9 wt.% 的纳米颗粒，其热导率升至 1.46。此外，还研究了在均匀热通量下通过圆管的层流状态条件下的对流传热。具有最高纳米颗粒负载量 (0.9 wt.%) 的纳米流体在雷诺数为 1713 时显示出最大的努塞尔数增强为 27.8%。研究了在均匀热通量下通过圆管的层流状态条件下的对流传热。具有最高纳米颗粒负载量 (0.9 wt.%) 的纳米流体在雷诺数为 1713 时显示出最大的努塞尔数增强为 27.8%。研究了在均匀热通量下通过圆管的层流状态条件下的对流传热。具有最高纳米颗粒负载量 (0.9 wt.%) 的纳米流体在雷诺数为 1713 时显示出最大的努塞尔数增强为 27.8%。