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標題: | 磁性奈米流體黏度的實驗研究 Experimental study on the viscosity of magnetic nanofluids |
作者: | You-Hsuan Yen 顏佑軒 |
指導教授: | 李雨 |
關鍵字: | 磁性奈米流體,四氧化三鐵粒子,黏度,磁場,老化效應, Magnetic nanofluid,Fe3O4 particles,viscosity,magnetic field,aging effect, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | 本文以改裝後之Brookfield黏度計(原理為環狀庫埃特流)對含四氧化三鐵粒子(Fe3O4)之磁性奈米流體的黏度進行實驗研究。該改裝後之黏度計其量測套筒改採塑膠製品、並在外圍套上螺線管線圈,以通過施加電流方式產生磁場。量測套筒與線圈皆浸入循環水箱中以消除焦耳熱產生的熱量,使待測流體在實驗過程中保持恆溫。改良後之黏度計與冷卻系統皆由前人研發,在這裡我們配製穩定懸浮的磁性奈米流體、並進行詳細的測試,以驗證磁性奈米流體作為一種智慧流體的可行性。
在本研究中,四氧化三鐵奈米粒子先採用經典的共沉澱法合成,以X射線衍射法測得粒子大小約9.7nm。然後在粒子表面包覆油酸以提供對抗凡得瓦力吸力的空間排斥力,避免粒子在流體中聚結;最後將包覆的粒子分散到基底流體中合成磁性奈米流體。我們採用真空泵油(VPO)與變壓器絕緣油(TO)兩種基底流體,合成Fe3O4-VPO奈米流體與Fe3O4-TO奈米流體,就其黏度在不同溫度(16oC – 30oC)、不同體積分率(0% – 4%)、不同磁場強度(0 – 100 高斯,於量測套筒頂部量測)及流體合成後不同時間(老化效應)進行量測。我們發現:(1)隨著溫度升高,奈米流體的黏度降低,但奈米流體與基底流體的黏度比值只呈微幅增加。(2)奈米流體的黏度值隨磁場強度與體積分率增加而提升。(3)通過施加重複磁場(在一個週期中磁場施加5分鐘,然後關閉5分鐘),發現磁性奈米流體的黏度可以根據需求由磁場“瞬間”調節,在磁場開啟時黏度快速增加但磁場關閉時黏度迅速恢復原值,且增加幅度與磁場強度成正比。(4)本實驗配製之奈米流體在磁場作用下為剪切稀化流體。(5)老化效應對Fe3O4-VPO奈米流體的影響較小,但對Fe3O4-TO奈米流體影響很大,因此Fe3O4-VPO奈米流體更適於應用。 Viscosity of magnetic nanofluid with Fe3O4 particles was studied experimentally using a modified Brookfield viscometer (based on circular Couette flow), with its cylindrical test section enclosed by an electric coil for generating the magnetic field through the application of an applied current. The test section together with the coil were immersed in a circulating water tank for removing the heat due to Joule heating, such that the test fluid was kept at a constant temperature during the experiment. Both the modified viscometer and the cooling system were developed by the previous investigators, and here we performed detailed tests of stable magnetic nanofluid fluids, for demonstrating that the magnetic nanofluids can potentially be served as a smart fluid. Fe3O4 particles were synthesized using the classical co-precipitation method, and their sizes were measured as around 9.7 nm using X-ray diffraction. The particles were then coated with oleic acid for providing repulsive steric force against van der Waals force, avoiding the coagulation of particles in liquid. The coated particles are then dispersed into base fluid for the synthesis of magnetic nanofluids. Two base fluids, vacuum pump oil (VPO) and transformer oil (TO), were used. The viscosities of Fe3O4-VPO nanofluid and Fe3O4-TO nanofluid were measured for different temperature (16oC – 30oC), different volume fraction (0% – 4%), different magnetic field strength (0 – 100 Gauss, measured at the top of the test section), and different times after the fluids were synthesized (aging effect). We found: (1) The viscosity of the nanofluid decreases, but the ratio of the viscosity of the nanofluid to that of the base fluid increases slightly, as the temperature increases. (2) The viscosity of the nanofluid increases with the magnetic field strength and volume fraction. (3) Through a repeated periodic excitation of applied magnetic field (field is on for 5 minutes and then off for 5 minutes within a cycle), it was found that the viscosity of magnetic nanofluid could be tuned “instantaneously” as desired by the magnetic field. In particular, viscosity was enhanced when the magnetic field was on, and recovered when the field was off; and the enhancement was proportional to the field strength. (4) The nanofluids in this study are shear thinning nanofluids under the action of magnetic field. (5) The aging effect is minor for Fe3O4-VPO nanofluid, but is substantial for Fe3O4-TO nanofluid. Thus the Fe3O4-VPO nanofluid is more appropriate for application. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/73757 |
DOI: | 10.6342/NTU201903864 |
全文授權: | 有償授權 |
顯示於系所單位: | 應用力學研究所 |
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