磁控鐵磁流體在平板渠道流與止推軸承系統之實驗

Experiment of a magnetically controlled ferrofluids in a flat plate channel flow and thrust bearing system

陳宇鳴(Yu-Ming Chen)

指導教授 ： 范憶華

中原大學/工學院/機械工程研究所/碩士(2014年)

https://doi.org/10.6840/cycu201400481

摘要

鐵磁流體為一種膠態混合物，由磁性固相微粒、基載液與表面活性劑結合而成。運動方式符合流體動力學，並有導磁率可受磁場控制。本文進行鐵磁流體特性研究，首先探討在相異間隙中的流動性，後觀察在各式磁場強度下的改變。磁場會顯著影響鐵磁流體的黏滯性，於同間隙的平板中控制外部磁場強度，檢測流動時間﹔後再固定磁場強度，檢測在各平板間隙的流動時間。由於需要比較與推算，採用相異體積分率與黏滯係數的鐵磁流體，目的於驗證磁場、鐵磁流體黏滯係數與基載液黏滯係數之關係式，並以較低基載液黏滯係數的鐵磁流體實驗數據來推算更高基載液黏滯係數下的流動形式。
在平板流實驗中，以d為兩平板間隙，M_v表示為垂直磁場強度，M_p為平行磁場強度。根據理論推導與實驗觀察可得知磁場走向與強度都會顯著影響在間隙中流動的鐵磁流體黏滯係數，原因在於間隙越小，粒子與截面的碰撞面積越大，導致黏滯係數變動，影響整體流動速率。實驗結果顯示當間隙越小，每分鐘鐵磁流體的流動量也越少，流動速率顯著的下降。低磁場下鐵磁流體的黏滯係數提升少，在寬間隙中對流動速率影響不大﹔當間隙越小時，同磁場下能減少的流動速率越多。若強磁場影響面積片佈一區段平板間隙，流動速率顯著下降，且當間隙小與鐵磁流體的基載液又為高黏滯性時，流動速率將會相當緩慢。
止推油腔上方有一鐵磁流體薄膜，下方銜接電磁鐵用於控制鐵磁流體，磁場走向垂直於鐵磁流體薄膜。本文依據油腔大小來決定外圍電磁鐵形狀，目的要求能夠集中磁場在上方磁性薄膜，使鐵磁流體黏滯性提高進而提升單腔附載能力。使用COMSOL分析結果可預知磁力將聚集於中心油腔位置，模擬量測中心油腔上緣與周邊磁通密度做比對，取得中心平均磁通強度高於周邊近二倍。而另一止推軸承使磁場集中在承載面上，實驗比對兩種設計的差異。在後續實驗中，紀錄變更磁場強度與上方負載重量，影響改變的油膜壓力與厚度。

關鍵字

鐵磁流體、磁場、黏滯係數

並列摘要

The phenomenon of a magnetic controlled ferrofluid flow in the flat plate laminar flow system is discussed in this paper. The ferrofluid flow is one kind of colloid mixture, which is composited by the magnetic particles, carrier fluid and surfactant. Its motion is followed the fluid dynamics and it is magnetic permeability and can be controlled by a magnetic field. From the theoretic analysis and the experimental test, the coefficient of viscosity of the ferrofluid flow will be affected by the magnetic field. Thus, an experimental rig is built to test the influences of the gap of the plate and the strength and direction of the magnetic field for several ferrofluid flows with different coefficient of viscosity. The experimental results showed that flow rate is proportional to the gap of the flat plate. The coefficient of viscosity of the ferrofluid flow is almost not upgrading in a wide gap condition by the magnetic field, but as the gap is smaller, the coefficient of viscosity will be promoted obviously. Furthermore, enhancing the magnetic field, it will be increase the coefficient of viscosity of the ferrofluid flow. From the experimental results, the relationship of the magnetic field, coefficient of viscosity of ferrofluid flow and the carrier fluid can be confirmed. And then we can to predict the dynamic of ferrofluid flow in a different carrier fluid with a higher coefficient of viscosity.
Magnetic fluid film on the top of Thrust bearing, the electromagnet below bearing is used to control the ferrofluid flow. The article based on the size of oil recess to determine the shape of the electromagnetic with the purpose of concentrating the magnetic field in the ferrofluid flow, and increasing the viscosity of ferrofluid flow that enhance the efficiency of Thrust bearing. Using COMSOL to analyze to know magnetic flied will be concentrating in the center of oil recess, and the other will be concentrating in the load surface. Using the experiment to know how the difference between two design, and record changes of film pressure and thickness by difference magnetic film and load weight.

並列關鍵字

ferrofluid flow、magnetic、viscosity

參考文獻

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