Ferrofluid droplet formation from a nozzle using alternating magnetic field with different magnetic coil positions

Abstract

Ferrofluid has been used in many fields, such as microfluidics, droplet formation, and heat transfer, due to its potential to be attracted in the presence of a magnetic field. Droplet formation, itself, has many applications such as emulsions, 3D micro-printers, MEMS, and electro-sprays. In this study, the mechanism of ferrofluid droplet formation from the nozzle in the presence of an alternating magnetic field was investigated. The magnetic coil was fixed at different angles with respect to gravity and the effect of the alternating magnetic field and the angle of the magnetic coil axis with respect to gravity on the produced droplet volume, satellite droplet, and droplet formation frequency were studied for the first time. Also, by using a reservoir instead of syringe pump, a drop-on-demand (DOD) platform was introduced. The results showed that with increasing magnetic force, the volume of droplets in both DC and AC cases decreases, whereas the droplet formation frequency increases. It was also observed that by using a DC magnetic field for all angles, the droplet formation was accompanied by a satellite droplet, whereas in the presence of the AC magnetic field, the satellite droplet was eliminated. So, a new regime of droplet formation was observed. Also, by tuning the alternating magnetic field, a larger droplet with respect to DC magnetic field was detected. Interestingly, it was shown that by increasing the angle of the magnetic coil axis with respect to gravity from zero to 90°, the volume of the produced droplet has a minimum at 45°.