Effect of a uniform magnetic field on a two-phase air-ferrofluid slug flow

Abstract

This paper presents an experimental study on the effect of a uniform magnetic field on a two-phase ferrofluid-air flow inside a capillary tube. A horizontal and transparent glass tube of 2.5 mm diameter is employed to investigate the dynamics of an intermittent ferrofluid slug flow under a 250G uniform magnetic field. Using a CCD camera and image processing, liquid slug front velocity and dynamic contact angle of the three-phase (ferrofluid-glass-air) flow were measured. To investigate the effect of slug length, a series of experiments were carried out with three distinct slug aspect ratios (α) of 8, 16, and 20. The slug aspect ratio is defined as the length of the slug divided by the diameter of the tube (α = L/D). It was observed that at the centre of the magnet, corresponding to maximum field strength, slug velocity was accelerated reaching its maximum value, and the dynamic contact angle was reversed from θ > 90° to θ < 90°. The smallest aspect ratio of liquid slug (α = 8) provides the optimum conditions for driving the slug flow using a magnetic field. It exhibits sharp deceleration after the magnet and significant changes in the dynamic of the contact angle. In addition, the influence of double magnets on a fixed slug aspect ratio (α = 8) is reported and compared with the case of a single magnet. It was observed that when two magnets are coupled, their combined pulling force operates, resulting in a high slug velocity at the first magnet position. Obtained experimental results revealed that both the number of magnets and slug aspect ratio are key parameters for the transport of ferrofluid in capillary tubes.