Aramide, Babatunde; (2022) Computational Modelling of Electrohydrodynamic Jetting (Taylor Cone Formation, Dripping & Jet Evolution): Case Study of Electrospinning. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Over the years, there has been growing interest in the phenomena that arise during fluid flow and electric field interactions. Manipulation of the flow and operating parameters gives rise to unique flow patterns that can be adapted for various applications ranging from field-like atomic ionization, microfluidics, electrospraying, electrospinning etc. This study aims to look at the critical phases of some of these processes and postulate how the electric field influences the fluid flow and vice versa. The electrohydrodynamic (EHD) equations coupled with the electrostatic equation describe this process mathematically and have been examined numerically in this study. Physical properties of water were used for the liquid medium, enveloped by air as applicable. The choice of media does not diminish the generality of the model. Both the liquid and the gaseous phases are active and interact via their contact surface. The conservation of mass and momentum, with appropriate additional force terms coming from the presence of the electric field (i.e., the EHD system) and the electrostatic equations were coupled together and solved using the Finite Volume method to simulate the flow- reflecting the effect of the fluid flow on the electric field and vice versa. The Volume of Fluid (VOF) technique was used to track the free surface. The solution procedure was such that the electric body forces were calculated from the electrostatic equation and then included in the Navier-Stokes equation to predict the velocity field and other fluid parameters. No initial shape was assumed for the fluid shape and charge distribution We have conducted a series of simulations, aiming to establish the model, to obtain test results and to examine, the influence of some of the parameters at play. Samples of such results obtained are presented in the relevant chapter of this report. Axisymmetric models were constructed, highlighting interesting features of these flows, like the formation of a Taylor cone, jet evolution, droplet break-up and fibre extrusion. This thesis focuses on some features from the early stages of the flows examined. Results agree well with both existing experimental and computational reports. Emphasis is placed on the generality methodology developed, that can handle geometric configurations of arbitrary complexity and any combination of liquid/gas. The interaction of the electric field with the fluid, as studied and analysed numerically in this work, offers great potential for control of emerging features.

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