ElectroHydroDynamic Atomisation

Unipolar and bipolar characterisation and modelling

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Abstract

ElectroHydroDynamic Atomisation (or electrospraying) is a way to disperse a liquid into droplets by exposing it to a strong electric field. The resulting droplets are (highly) charged and can exhibit narrow size and charge distributions which is desirable for many applications. In this dissertation a novel method is developed to classify the spray mode of an electrospray system. Unlike the previously proposed classifications, this method does not require optical observations, making it ideally suited for application in larger scale systems or in systems where optical access is problematic. The efficiency of electrospraying was also determined. Although only conservative estimates of the efficiencies could be obtained, it was found that for certain spray modes the efficiency was > 1 indicating an energy increase. The second part of this thesis focuses on the optimisation of a bipolar coagulation reactor: a reactor in which (highly) charged particles with opposite polarities selectively coalesce, resulting in for example coated or reacting particles. A 2D fixed-sectional population balance model was developed to make numerical simulations of the coagulation process feasible. To optimise a bipolar coagulation reactor, a 3D grid of coupled modelling cells was used where in each individual modelling cell the coagulation behaviour was determined using the just mentioned 2D fixed-sectional population balance model. Using this approach optimisations were possible with respect to many factors like for example the relative placement of the individual nozzles or the introduction of ions at certain locations. The modelling results were qualitatively validated by combined Particle Image Velocimetry (PIV) and two-colour Laser Induced Fluorescence (LIF) measurements in a rectangular bipolar coagulation reactor.