磁性液滴運動與感應電動勢之研究

Abstract

磁性流體（EMG905）置於不可互溶之流體中，磁性液體感磁後通過感應線圈，產生其感應電壓。經實驗後繪製感應電壓與磁液滴移動軌跡圖，擷取與其時間點所對應之磁液滴位置。其目的為希望找出在不同條件下有無其規律性。針對磁液滴受垂直磁場影響之流動型態，本文根據實驗結果分為三階段進行分析，第一階段為磁性液滴受磁場影響較小，因此移動速度與變形較小。第二階為磁性液滴受磁場梯度影響，產生大幅度之拉伸行為。第三階段為磁性液滴抵達是管底部後，液滴持續拉伸的行為。結果發現在相同體積下，磁場大小對於訊號振幅之比值變化最大在1.5倍，而相同磁場不同體積之情形訊號振幅之比值變化最大可達到4倍。磁液體之體積，對磁液體流動速度之影響大於磁場對於液滴速度之影響。因此當磁液體體積小時流動速度快、磁通量小，當磁液體體積大時磁通量大、但是速度慢。因此針對感應電壓之效率而言，並不是單純增加液體體積或增大磁場即可。在本實驗條件中，歸納出磁液體體積與磁鐵顆數在何者情況下，其發電效率為最佳。模擬方面，本文利用商用軟體求解Maxwell’s方程式，進而模擬實際之實驗問題。本文利用實驗條件作為模擬之設定。利用模擬與實驗之液滴前端速度做比較，其結果顯示兩者之速度趨勢相同，因此可做定性上之比較。

In this paper, we have demonstrated the capabilities to catch the signals of induced electromotive force (EMF). The characteristics of EMF signals are analyzed systematically. Influences of volumes, sizes and travelling velocities of ferrodrop on the magnitudes and wave spans of the signals are presented. In addition, simulations of the induction fields are carried out to provide the physical insights of the induced EMF signals. The signals can be potentially applied as diagnostic characteristics in the measurements of travelling velocities or sizes of moving ferrodrop. The magnetized ferrodrop vertically pass through an induction coil when immiscible ferrodrop placed in a viscous medium. Effects of various parameters, such as volumes of ferrodrops and intensity of external magnetic field. According to results, volumes of ferrodrop affected amplitude of signal. Intensity of magnetic field affected size of signal. The motion of a ferrodrop placed in a viscous medium and driven by an externally applied magnetic field is investigated numerically in an axisymmetric geometry. Initially, the drop is spherical and placed at a distance away from the magnet. The governing equations are the Maxwell equations for a non-conducting flow, momentum equation and incompressibility.