10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Scaling-up of Extractor-Free Electrohydrodynamic Emitter Arrays in Linear Configuration
Nikolas Sochorakis, Jordi Grifoll, JOAN ROSELL-LLOMPART, Universitat Rovira i Virgili
Abstract Number: 1394 Working Group: Materials Synthesis
Abstract Simultaneous operation of multiple electrospray emitters (multiplexing) have been used in virtually every known application of electrospray, to achieve relevant production rates: Pharmaceutical particle synthesis, surface coating, micro-electronics cooling, mass spectrometry in nanoelectrospray mode, microprotein arrays, 3D printing, microcombustion, and colloidal propulsion of spacecraft. Most often, electrospray emitters are arranged either in square or hexagonal 2D patterns, or in a straight line, as in the present study. When the concentration of the emitters is raised, the electrostatic interactions between the Taylor cones result in non-uniform electrical field, which can interfere with the spraying. Therefore, an important aim in this field is the development of configurations which allow robust, stable spraying.
Often, to achieve this goal, the electrospray emitters are positioned very near the counter electrode. In this way, the Taylor cones are shielded from one another and from the spray charges. When such counter electrode is a conducting ring or perforated plate, in order to extract the generated aerosol, this electrode is called 'extractor'. Since operating configurations with extractor electrodes can become challenging, at the beginning of this research we had reasoned that they would not be required in 1D arrays. Therefore, we have developed and evaluated extractor-free linear designs. In them, the counter electrode is much farther from the Taylor cones than the inter-cone spacing (or pitch) (about 4 times or more), and 'blind emitter' electrodes are placed at the ends of the array. At the same time, a backplate electrode is positioned behind the emitters, set at the same electrical potential.
We have characterized the conditions leading to stable cone-jet mode and spray plume behaviour as a function of the geometrical parameters of the arrays and the relevant liquid properties (e.g. electrical conductivity). We find that:
(1) It is possible to produce stable spraying along the entire linear array without the aid of extractor-type electrodes, over wide ranges of the applied voltage, using two blind emitter electrodes are located at either end of the array;
(2) The electrical potential difference needed to sustain stable spraying increases with the number of spraying emitters in the array, yet tends towards an asymptotic value, thus becoming finite regardless of array length;
(3) In long arrays, there are three distinct regions: an 'inner' central region, in which the sprays shapes are similar, unaffected by the length of the array; and two 'outer' regions, located at the ends of the array, where 'end effects' are concentrated, in which the sprays become broader.
(4) At high electric field strength, the spray symmetry breaks, as the Taylor cones retract towards the emitter tube (upstream) while they misalign, similarly as found for electrospying from single emitters, except in the linear array the direction of the emission is "seeded" by errors in the emitters' positions.