Marin Catalin N, Malaescu Iosif
West University of Timisoara, Faculty of Physics, Bd. V. Parvan nr. 4, 300223, Timisoara, Romania.
Eur Phys J E Soft Matter. 2020 Sep 29;43(9):61. doi: 10.1140/epje/i2020-11986-3.
The effect of the strength and orientation of magnetic field with respect to the temperature gradient on the effective thermal conductivity [Formula: see text], in a kerosene-based ferrofluid with magnetite particles is reported. A new theoretical model to explain the experimental dependence [Formula: see text], 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 [Formula: see text], 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 [Formula: see text]. 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.
报道了在含有磁铁矿颗粒的煤油基铁磁流体中，磁场强度和方向相对于温度梯度对有效热导率[公式：见原文]的影响。基于西拉斯方程（首次为此目的应用于铁磁流体），提出了一种新的理论模型来解释对于磁场相对于温度梯度的平行和垂直取向所获得的实验依赖性[公式：见原文]。为了计算[公式：见原文]，我们考虑到排列在场诱导微结构中的颗粒团聚体具有椭球体形式，并且椭球体的长轴与短轴之比a/b随着磁场强度的增加而增大。使用所提出的理论模型，我们首次建立了相对于温度梯度平行和垂直的H情况下，a/b比值与磁场H之间的半经验关系，进而确定了[公式：见原文]对H的依赖性。理论结果与实验测量结果一致。所报道的结果具有重要的实际意义，表明铁磁流体可用于磁可调热传递装置或其他潜在的热应用中。
