Improvements of on-demand electrohydrodynamic injection of droplet and droplet pair in a dielectric liquid

WOS:000551631000036This paper deals with the extraction from a meniscus of water droplets of small size into an immiscible insulating liquid by the use of a multistage voltage pulse. A previous study on a particular oil established that this EHD Drop-on-demand technique allows producing droplets of size smaller or much smaller than the needle diameter. The case of a dielectric liquid characterized by a rather high value of the water/oil interfacial tension is considered here. It is shown that by adequately modifying the shape and level of the multistage voltage pulse, droplets are produced with a diameter ranging over a large interval. It was expected that the short enough pulse duration would give electrically neutral droplets; in practice it is found that the droplets carry minute but nonzero charges. An explanation is given for the charging mechanism and other changes of the pulse shape allow to further minimize the droplets charge. Finally having in mind the possibility to investigate experimentally the electrocoalescence of two close drops, results are presented concerning the injection of two successive droplets. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved