Abstract Overheating of power electronic devices has become a significant issue due to their continued miniaturization and increased heat flux that needs to be dissipated. Ferrofluids (magnetic nanofluids) have been shown to have higher thermal conductivity than their base aqueous or oil based fluids due to the solid magnetic nanoparticles that make up the ferrofluid. This allows higher convective heat transfer rates and, importantly, the ability to externally effect the flow using a magnetic field. In this paper, we focus on material characterization of ferrofluids and measurement of heat transfer rates for single-phase ferrofluidic forced convective flow in microchannels. We show that heat transfer properties of the flow are enhanced with the use of ferrofluids and that the material make-up of the ferrofluid affects these properties. In this paper, we argue that generally, convective heat transfer rates for ferrofluids are increased by increasing the solid volume concentration of magnetic particles (∼0.2–0.4%). Interestingly, increasing magnetic flux was shown to decrease heat transfer enhancement. This was due to a reduction in the thermal conductivity of the bulk fluid caused by magnetic nanoparticles being drawn out of the isotropic mixture and becoming pinned to the channel wall in the region of strongest magnetic field. We show that there is good correlation between both theory and experimental visualization of this phenomenon.

中文翻译：

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用于外磁场下传热增强的铁磁流体

摘要 由于电力电子设备的持续小型化和需要消散的热通量增加，其过热已成为一个重要问题。由于构成铁磁流体的固体磁性纳米颗粒，铁磁流体（磁性纳米流体）已被证明比它们的基础水或油基流体具有更高的热导率。这允许更高的对流传热率，并且重要的是，能够使用磁场从外部影响流动。在本文中，我们专注于铁磁流体的材料表征和微通道中单相铁磁流体强制对流的传热率测量。我们表明，使用铁磁流体可以增强流体的传热特性，并且铁磁流体的材料组成会影响这些特性。在本文中，我们认为通常通过增加磁性颗粒的固体体积浓度（~0.2-0.4%）来增加铁磁流体的对流热传递率。有趣的是，增加磁通量被证明会降低传热增强。这是由于磁性纳米颗粒被从各向同性混合物中抽出并在最强磁场区域被固定在通道壁上而导致大量流体的热导率降低。我们表明，这种现象的理论和实验可视化之间存在良好的相关性。增加的磁通量被证明会减少传热增强。这是由于磁性纳米颗粒被从各向同性混合物中抽出并在最强磁场区域被固定在通道壁上而导致大量流体的热导率降低。我们表明，这种现象的理论和实验可视化之间存在良好的相关性。增加的磁通量被证明会减少传热增强。这是由于磁性纳米颗粒被从各向同性混合物中抽出并在最强磁场区域被固定在通道壁上而导致大量流体的热导率降低。我们表明，这种现象的理论和实验可视化之间存在良好的相关性。