Stable multi-jet behavior of ethanol under an electric field

Abstract

Electrospray is a mass transfer technology in which charged liquid is broken into fine droplets/particles with ideal monodispersity, easy controllability, and high-deposition . In recent decades, with the rapid development of various micro precision instrument technologies, the research of electrospray has been widely applied to micro/nano-scaled thin film and particle preparation, air purification, micro-combustion, space micro-propulsion, mass spectrometry, and biotechnology. Previous researches mainly focused on the stable cone-jet mode that has the advantages for producing several micron-sized particles or droplets with good stability and monodispersity. However, electrospray in this cone-jet mode has a major disadvantage that restricts the practical application of electrospray. The droplet size in the cone-jet mode increases with an increase of the flow rate, and this means the production of tiny droplets limits the supply flow rate, and this limited flow rate cannot meet the requirements for atomization flow in practical application. Multi-jet is an important operation mode in electrospray, and sub-droplets of comparable size to the sub-droplets produced by cone-jet can be obtained on the basis of multiplication of the single capillary flow. However, multi-jet atomization is very unstable, and it is difficult to attain a stable jet atomization state; therefore, in-depth research on the evolution of its morphology and atomization characteristics is necessary to expand the practical application of electrostatic atomization technology. Based on high-speed photography technology with a high spatial-temporal resolution, the influence of capillary geometry, electrode spacing, liquid supply flow rate, and applied voltage on the multi-jet formation and evolution in electrospray was studied in detail. The electric bond number and the dimensionless flow rate were introduced to describe their action laws on the evolution behavior of the stable jet number, stable atomization range, and jet deviation angle in the stable multi-jet mode. The research results show that the range of the number of stable jets N of multi-jet is from 2 to 10. When 2≤ N N ≤10, the jets are ejected from the outer edge of the capillary orifice to form an edge jet mode, and it is particularly important to note that the occurrence frequency of the stable 5–8 strands is higher than other strands. In the edge mode, as the number of stable jets increases, the range of the electric bond number of the stable multi-jets and the critical minimum electric bond number gradually increases, and a voltage switching phenomenon of stabilizing multi-jet is also presented. As the dimensionless flow rate increases, the maximum value of the electric bond number under each number of stable jets shows a linear growth trend. The maximum value of the electric bond number increases with the increase of the stable jet number under the same flow rate, and a significant increase in the minimum value of the electric bond number is observed. Additionally, as the number of stable jets in the edge mode increases, the overall deviation angle of the jet increases, but the range of variation of the deviation angle of each stable jet number is controlled within 5°±0.3°. Moreover, as the electric bond number increases, the jet deviation angle gets closer to 45°, which indicates that the electric field force dominates the jet deviation as the electric field intensity increases.