<p>Large scale and cost-efficient synthesis of carbon nanostructured
materials has garnered tremendous interest over the last decade owing to their
plethora of engineering and bio-science applications. One promising method is
roll-to-roll radio frequency chemical vapor deposition and this work presents a
computational investigation of the capacitively coupled radio frequency plasma
in such a system. The system operates at moderate pressures (less than 30 mbar)
with an 80 kHz square wave voltage input. The computational model aids the
understanding of plasma properties and α-γ transition parameters which strongly
influence the nanostructure deposition characteristics in the system. One
dimensional argon and hydrogen plasma models are developed to characterize the
effects of input voltage, gas pressure, frequency, and waveform on the plasma
properties. A hybrid mode which displays the characteristics of both α and γ
discharges is found to exist for the low cycle frequency 80 kHz square wave
voltage input due to the high frequency harmonics associated with a square
waveform. The threshold voltage at which the transition between the different
regimes occurs is higher for hydrogen than for argon owing to its diatomic
nature. Collision radiative modeling is performed to predict the argon emission
intensity in the discharge gap. The results are found to lie within 16% of the
optical emission spectroscopy measurements with better agreement at the center
of the discharge, where the measurement uncertainty is low and the emission by
ions is not significant. A quasi-zero dimensional steady state chemistry model
which uses the hydrogen plasma properties as inputs predicts high
concentrations of C<sub>2</sub>H, C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>3</sub><sup>+</sup>,
C<sub>2</sub>H<sub>4</sub><sup>+ </sup>and C<sub>2</sub>H<sub>6</sub><sup>+</sup><sub>
</sub>during carbon nanostructure deposition.</p>
<p> </p>
<p>Carbon nanostructures
are popularly used as field emitters. Field emission based microplasma
actuators generate highly non-neutral surface discharges that can be used to
heat, pump, and mix the flow through microchannels and offer an innovative
solution to the problems associated with microcombustion. They provide a
constant source of heat to counter the large heat loss through the combustor
surface, they aid in flow transport at low Reynolds numbers without the use of
moving parts, and they provide a constant supply of radicals to promote chain
branching reactions. This work presents two actuator concepts for the
generation of field emission microplasma, one with offset electrodes and the
other with planar electrodes. They operate at input voltages in the 275 to 325
V range at a frequency of 1 GHz which is found to be the most suitable value
for flow enhancement. The momentum and energy imparted by the charged particles
to the neutrals as modeled by 2D Particle-In-Cell with Monte Carlo Collisions
(PIC/MCC) are applied to actuate flow in microchannels using 2D Computational
Fluid Dynamics modeling. The planar electrode configuration is found to be more
suitable for the purpose of heating, igniting and mixing the flow, as well as
improving its residence time through a 10 mm long microcombustor. The
combustion of hydrogen and air with the help of 4 such actuators, each with a
power consumption of 47.5 mW/cm, generates power with an efficiency of 28.8%.
Coating the electrode surface with carbon nanostructures improves the combustion
efficiency by a factor of 2.5 and reduces the input voltage by a factor of 6.5.
Such microcombustors can be applied to all battery based systems requiring micropower
generation with the ultimate goal of “generating power on a chip'”.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/9037487 |
| Date | 15 August 2019 |
| Creators | Gayathri Shivkumar (7038164) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Coupled_plasma_fluid_and_thermal_modeling_of_low-pressure_and_microscale_gas_discharges/9037487 |
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