The effect of a non-uniform pulse-width modulated magnetic field with different angles on the swinging ferrofluid droplet formation

In this study, ferrofluid droplet formation from a nozzle in the presence of a non-uniform Pulse-Width Modulated (PWM) magnetic field with different angles was studied experimentally. A Drop-on-Demand platform was introduced and three different regimes of droplet formation were observed. The regime map of the droplet formation was presented. A new type of droplet formation evolution was observed in which the droplet is formed while it is swinging around the nozzle, and the satellite droplet is not generated in this regime. The effects of five important parameters including magnetic flux density, applied magnetic frequency, duty cycle, distance between the nozzle and the center of the upper surface of the coil, and the angle of magnetic coil with respect to gravity on droplet diameter, formation frequency, number of pulses for one droplet generation, and droplet formation evolution were investigated. Results demonstrated that by increasing the magnetic flux density and duty cycle, and by decreasing applied magnetic frequency, the droplet diameter decreases, whereas the formation frequency increases. Also, the minimum droplet diameter was observed at the distance of 10 mm and the angle of 45 degrees. Finally, a correlation for dimensionless droplet diameter was proposed with an average relative error of 2.8%. (C) 2020 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.