The field of microfluidics is developing with advances in MEMS (micro electro-mechanical system) and μ-TAS (micro total analysis system) technologies. In various devices, controlling the flow rate of liquid or gas accurately at micro or nanoliter volume levels is required. By using a ferrofluid, the flow of a liquid or gas in a microchannel can be controlled by the driving power exerted on the ferrofluid. In this study, an unsteady flow of a liquid slug caused by the driving force exerted by a ferrofluid has been investigated in a 200μm circular microchannel under the influence of an external magnetic field. The motion and behavior of the liquid slugs were observed. Thus, by visualizing the behavior and interface of the ferrofluid and the liquid slug, we could study the characteristics of fluid transport phenomena in the microchannel. The relationship between the movements of the liquid slug and the ferrofluid was investigated experimentally and analytically. The surface tension and kinematic viscosity of the liquid significantly affected the movement of the liquid slug. Therefore, the velocity of the ferrofluid is affected by the physical properties of the liquids pulled. Combinations of various liquids with a ferrofluid were examined in this study. The velocity of a short liquid slug was obtained and compared with the velocity of the ferrofluid. Also an apparent surface tension of the sample liquid was examined analytically.

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