Abstract.

The effect of the strength and orientation of magnetic field with respect to the temperature gradient on the effective thermal conductivity \(\lambda_{eff}(H)\), in a kerosene-based ferrofluid with magnetite particles is reported. A new theoretical model to explain the experimental dependence \(\lambda_{eff}(H)\), obtained for both the parallel and perpendicular orientation of the magnetic field, relative to the temperature gradient is proposed, based on the Sillars equation (which is applied for the first time to a ferrofluid in this purpose). For computing \(\lambda_{theor}\), we have considered that the particle agglomerations, arranged in field-induced microstructures, have ellipsoid forms and the ratio a/b between the major axis and the minor axis of the ellipsoid increases with increasing the magnetic field strength. Using the proposed theoretical model, we established for the first time a semi-empirical relationship between the ratio, a/b and the magnetic field, H, both for parallel and perpendicular H relative to the temperature gradient, determining then the dependence on H of \(\lambda_{theor}\). The theoretical results are in agreement with the experimental measurements. The reported results are of great practical importance and show that ferrofluids may be useful for incorporation in magnetic tuneable heat transfer devices or for other potential thermal applications.

Graphical abstract

中文翻译：

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磁场作用下铁磁流体导热系数的实验和理论研究

摘要。

报道了在具有磁铁矿颗粒的煤油基铁磁流体中，磁场强度和取向相对于温度梯度的影响对有效导热率\（\ lambda_ {eff}（H）\）的影响。基于Sillars方程，提出了一个新的理论模型来解释相对于温度梯度的磁场的平行和垂直方向所获得的实验依赖性\（\ lambda_ {eff}（H）\）。为此首次将其应用于铁磁流体）。为了计算\（\ lambda_ {theor} \），我们认为布置在场致微观结构中的粒子团块具有椭球体形式，且比率a / b椭圆形的长轴和短轴之间的“α”随磁场强度的增加而增加。使用所提出的理论模型，我们首次建立了相对于温度梯度的平行和垂直H的比率a / b与磁场H之间的半经验关系，然后确定对H的依赖关系。\（\ lambda_ {theor} \）。理论结果与实验结果吻合。报道的结果具有很大的实践意义，并且表明铁磁流体可用于结合在磁性可调节的传热装置中或用于其他潜在的热学应用。

图形概要