|dc.description.abstract||The operational environment of colloid thrusters is high vacuum (10-3 _ 10-6 mbar)
however, much of the experimental data collected to date to identify parameter
relationships in cone jet mode electrosprays (ES), such as current-volumetric flow
rate scaling laws, has been conducted in atmospheric conditions. This highlights a
need for electrospray data under high vacuum conditions.
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.
An online flow measurement system is described, which has been developed during
this research to measure the fluid volumetric flow rate, concurrently with applied
voltage and spray properties such as spray current and cone, jet and spray geometry.
This automated flow measurement system was used to measure flow rates as low as
InUs with an absolute accuracy of 0.3nUs and a resolution of 0.03nus. It is
identified that this system may be easily adapted for lower flow rates and higher
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 -4nLIs 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 Gahan-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
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/Nal 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.||en_US