In this study, the duration of sonication efficacy on the thermal conductivity of Fe3O4-liquid paraffin nanofluid is investigated. The nanofluid is produced at 0.005, 0.01, 0.015, 0.02, 0.025 and 0.03 vol concentrations by applying two-step method. The sonication process is performed in a temperature range of 20-90 °C. The duration of sonication seems to have two important effects: On the one hand, increasing the duration of sonication breaks the nanoparticles clusters, hence distributes the nanoparticles more uniformly which in turn rises thermal conductivity. On the other hand, an excessive increase in the duration of sonication can impair nanofluid stability. The results of experimental tests proved that the optimal duration of sonication is 3 h. The optimal duration of sonication is not dependent on the nanoparticles volume fraction (φ) and temperature. It was found that at the highest temperature and φ (90 °C,0.03), the greatest thermal conductivity enhancement (28.49%) is obtained. In contrast, at the lowest temperature and φ (20 °C,0.005) the lowest thermal conductivity enhancement was obtained (2.82%).

中文翻译：

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超声处理时间对Fe3O4-液体石蜡磁性纳米流体导热系数的影响：实验评价。

在这项研究中，研究了超声处理持续时间对Fe3O4-液体石蜡纳米流体的热导率的影响。通过应用两步法，可以以0.005、0.01、0.015、0.02、0.025和0.03的体积浓度生产纳米流体。超声处理在20-90°C的温度范围内进行。超声处理的持续时间似乎具有两个重要的影响：一方面，增加超声处理的持续时间会破坏纳米颗粒的团簇，从而使纳米颗粒更均匀地分布，从而提高热导率。另一方面，超声处理持续时间的过度增加会损害纳米流体的稳定性。实验结果表明，超声处理的最佳时间为3 h。超声处理的最佳持续时间不取决于纳米颗粒的体积分数（φ）和温度。发现在最高温度和φ（90°C，0.03）下，可获得最大的导热率提高（28.49％）。相反，在最低温度和φ（20°C，0.005）下，获得的最低导热系数提高（2.82％）。