The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

中文翻译：

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提高太阳能集热器热性能的策略

本文评估了一种改善热交换器传热的被动方法，这意味着使用纳米流体。所有计算均以恒定体积流量进行。该研究检查了 CuO、MgO 和 Al 体积浓度为 0–4% 的三种流体2氧3粒子。结果表明传热系数随着温度的升高而增加。安阿尔2氧3纳米流体（4% 浓度）有助于实现最佳热性能。掺入 4% 含量的 MgO 可使传热增强 15% 至 22%，而类似浓度的 CuO 则可显着增强 25%。值得注意的是，Al纳米粒子的引入2氧3传热性能显着增强，潜在改进高达 36%。根据几种纳米粒子（Al2氧3, 氧化铜, 二氧化硅2和 ZnO），体积百分比在 1-4% 范围内，纳米颗粒直径为 25-70 nm。对于所有纳米流体，时间平均努塞尔数随固相体积分数增加不到 5% 而增加。