Effect of size and stretch of a moving ferrofluid drop on induced electromotive force

Ch.-Y. Chen¹ - Sh.-Y. Wang¹ - Ch.-Y. Wen² - Ch.-Sh. Jan¹

¹ Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
² Department of Mechanical Engineering, Hong Kong Polytechnic University, Hong Kong, China

Abstract
Application for obtaining useful global features, e.g. the size and stretch of a moving ferrofluid drop by analyzing the characteristics of the induced electromotive force signal is demonstrated. These features are highly relevant to two maximum magnitudes in the electromotive force signal, e.g., the positive (V₁) and the negative (V₂) peak respectively induced when the drop enters and leaves the region covered by the induction coil. Favorable induction conditions of these two maximum magnitudes are opposite. In general, V₁ increases with the size of the ferrofluid drop because of stronger magnetization. On the contrary, V₂ is more prominent for a smaller drop, whose stretch is less significant. As a result, the ratio of |V₁/V₂| monotonically increases with the size of the ferrofluid drop. This finding suggests that the induced EMF signal can be used as a useful tool for quantifying the flow conditions, such as the size and stretch of moving ferrofluids. Figs 8, Refs 13.