粒徑分佈對以煤油為基底磁性奈米流體磁黏效應的影響

Effect of Particle Size Distributions on Magnetoviscosity of Kerosene-based Magnetic Nanofluids

廖志成(Zhi-Cheng Liao)

指導教授 ： 李雨

國立臺灣大學/工學院/應用力學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202203294

摘要

磁性奈米流體為穩定懸浮有磁性奈米粒子之懸浮液。透過外加磁場可改變其黏度，稱為磁黏效應。磁黏效應隨磁場、流場剪應變率、及粒徑大小分布等而異。本研究以實驗方法、透過對七種不同大小粒徑分布的四氧化三鐵-煤油磁性奈米流體進行粒徑和黏度量測，以研究粒徑大小對磁黏效應的影響。本文以永久磁鐵塊產生磁場、以狹縫黏度計量測黏度、以磁性粒徑分析(Magnetogranulometric method)及動態光散射(Dynamic light scattering)量測懸浮狀態下的粒徑分佈。
主要成果如下: (1) 在不同溫度下，以共沉澱法生成兩種不同大小粒徑的Fe3O4奈米粒子，稱SP及BP粒子，其z平均粒徑分別為15 nm及40 nm；再在該兩種粒子中採五種不同數量比例的組合，以二步法配製出共七種不同大小粒徑分布的四氧化三鐵-煤油磁性奈米流體。該等流體的磁化強度和商用鐵磁流體APG 513A者相當。按磁性粒徑分析，粒徑峰值分別為12、16、18、20、21、24及28 nm。(2)就上述七種流體，在五種剪切率(44s1, 67 s1, 90 s1, 111 s1, 及180 s1) 、三種磁場強度(200、350及500 Gauss)及兩種磁場方向(垂直或平行於渦度)下進行了黏度量測。(3)磁場強度越大，磁黏增益越佳。以SP粒子配製的流體為例，在剪切率44 s1下，當磁場強度由200 Gauss增為500 Gauss時，磁黏增益至200 Gauss時的兩倍。但同在200 Gauss下，BP粒子配製的流體，其磁黏增益為SP粒子者的四倍。流體中大粒子佔比越高，其磁黏增益越大。(4)磁場方向垂直渦度時，其磁黏增益優於平行方向者。以SP粒子配製的流體為例，在剪切率44 s1和磁場強度500 Gauss下，平行狀況者的磁黏增益為40%，垂直狀況者則為70%；但以BP粒子配製的流體，在平行狀況的磁黏增益為75%，垂直渦度時則為97%。(5)剪應變率越大，磁黏增益愈差；但流體中含有較多大顆粒子可助降低此剪切稀化效應。

關鍵字

四氧化三鐵粒子 ； 磁性奈米流體 ； 狹縫黏度計 ； 磁黏效應 ； 粒徑分布 ； 磁性粒徑分析

並列摘要

Magnetic nanofluid is a liquid suspended stably with nanoparticles. Magnetovis-cosity is the change of viscosity of magnetic nanofluid through an application of mag-netic field. It depends on magnetic field, shear rate of the flow, and size distribution of the suspended particles. In order to study the effect of particle sizes on magnetoviscosi-ty, particle sizes and fluid viscosity were measured for seven Fe3O4-Kerosene magnetic nanofluids with different size distributions. The magnetic field was generated using permanent magnetic plates, the viscosity was measured using a slit viscometer, and the particle sizes were accessed using magnetogranulometric analysis and dynamic light scattering in suspended states.
The main findings are as follows. (1) Two different particles, called SP and BP, were generated using coprecipitation method at different temperature, with z-average diameter 15 nm and 40 nm, respectively. Two-step method was employed for the syn-thesis of seven Fe3O4-Kerosene nanofluids using SP, BP, and different combination of SP and BP. The magnetization of those seven fluids are similar to that of APG513A, a commercial ferrofluid。The peak values of the particle size distributions are 12、16、18、20、21、24及28 nm, respectively for those seven fluids according to magnetogranu-lometric analysis. (2)Viscosity measurement for those seven fluids were measured for five shear rates (44 s1, 67 s1, 90 s1, 111 s1, and 180 s1), three magnetic field strengths (200、350 and 500 Gauss), and two magnetic field directions (perpendicular and parallel to the vorticity). (3) Viscosity enhancement is increased as the magnetic field strength increases. For fluid synthesized using SP particles, viscosity enhancement at 500 Gauss is twice the value of that at 200 Gauss under a shear rate 44 s1. However, the enhance-ment is 4 times the value of that at 200 Gauss if the fluid is synthesized using BP parti-cles. More larger particles in the fluid, more the viscosity enhancement. (4) Viscosity enhancement is better when the magnetic field is perpendicular to the vorticity rather than that parallel to the vorticity. For fluid synthesized using SP particles, the viscosity enhancement is 40% and 70% for magnetic field parallel and perpendicular, respectively, to vorticity, under shear rate 44 s1and field strength 500 Gauss. However, the en-hancement is 100% for the parallel case if the fluid is synthesized using BP particles. (5) Viscosity enhancement decreases as the shear rate increases. Such shear thinning effect could be weakened if more larger particles are in the fluid.

並列關鍵字

Magnetic nanofluids ； Magnetoviscosity ； Particle size distribution ； Magnetogranulometric analysis ； Slit viscometer

參考文獻

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