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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Characterisation of electrospary properties in high vacuum with a view to application in colloid thruster technology

Author: SMITH, K

Year: 2005

Supervisor(s): John Stark

Electrospray experimental data was collected using medium conductivity solutions (0.0025 -0.0160 S/m) of TEG doped with sodium iodide in high vacuum. These sprays were obtained from a stainless steel capillary and a disk counter electrode with central aperture.

The ES data collected demonstrates, for the first time, the detailed dependence of volumetric flow rate upon the applied voltage. The sensitivity of nominal flow rate to applied voltage was found to be higher for lower nominal flow rates. For a volumetric flow rate ~4nL/s a 25% a change in flow rate per kV was recorded over a cone-jet mode stability range spanning ~1.5kV. This volumetric flow rate voltage sensitivity holds particular significance for colloid thruster systems, which operate at or near minimum flow rate conditions.

The current was found to have a power law dependence on flow rate similar to the current scaling laws of F. de la Mora and Ganan-Calvo however the exponent of this power law differs significantly from these scaling laws. A study considering the effect of charge carrier mobility in simple 1:1 electrolytes shows that the exponent of the power law current-flow rate scaling increased with increasing charge carrier mobility.

Contrary to the various scaling laws the spray current was found to be dependent on electrostatic conditions. The sensitivity of the emitted current to the applied voltage was also found to increase with increasing nominal volumetric flow rate.

The geometrical parameters of cone angle, spray angle and jet length were measured for varying TEG/NaI solution conductivity. Cone geometry was found to be relatively independent of conductivity in the range tested. Jet length was found to have an inverse relationship with solution conductivity.