How do the barrier thickness and dielectric material influence the filamentary mode and CO₂conversion in a flowing DBD?

Abstract

Dielectric barrier discharges (DBDs) are commonly used to generate cold plasmas at atmospheric pressure. Whatever their configuration (tubular or planar), the presence of a dielectric barrier is mandatory to prevent too much charge build up in the plasma and the formation of a thermal arc. In this article, the role of the barrier thickness (2.0, 2.4 and 2.8 mm) and of the kind of dielectric material (alumina, mullite, pyrex, quartz) is investigated on the filamentary behavior in the plasma and on the CO2 conversion in a tubular flowing DBD, by means of mass spectrometry measurements correlated with electrical characterization and IR imaging. Increasing the barrier thickness decreases the capacitance, while preserving the electrical charge. As a result, the voltage over the dielectric increases and a larger number of microdischarges is generated, which enhances the CO2 conversion. Furthermore, changing the dielectric material of the barrier, while keeping the same geometry and dimensions, also affects the CO2 conversion. The highest CO2 conversion and energy efficiency are obtained for quartz and alumina, thus not following the trend of the relative permittivity. From the electrical characterization, we clearly demonstrate that the most important parameters are the somewhat higher effective plasma voltage (yielding a somewhat higher electric field and electron energy in the plasma) for quartz, as well as the higher plasma current (and thus larger electron density) and the larger number of microdischarge filaments (mainly for alumina, but also for quartz). The latter could be correlated to the higher surface roughness for alumina and to the higher voltage over the dielectric for quartz.

Electrical Diagnostics of Dielectric Barrier Discharges

“…A small diameter current probe embedded in a larger planar DBD has also been used, but only to obtain data on individual current pulses [57,60,61]. Many literature sources use relatively large electrode surface areas >1 cm 2 , combined with direct digital post-processing on the DBD current i(t) to determine single filament properties [62][63][64][65][66][67][68]. In this section, results are presented for a plane-parallel DBD with a surface area of 7 mm 2 , large enough to have multiple interacting filaments per halfcycle, but small enough to prevent significant overlap between them in time.…”

Numerical investigation of co-axial DBD: Influence of relative permittivity of the dielectric barrier, applied voltage amplitude, and frequency

“…3,6,11 It should be noted that the dimensions of the DBD reactor and dielectric layer have also been shown to influence the discharge. [26][27][28] However in this work, the dimensions are fixed and the effects of relative permittivity of the dielectric barrier and the applied voltage amplitude and frequency are investigated in detail. The inner electrode is grounded and the outer electrode is connected to a high voltage AC power supply.…”

“…The higher conversion obtained with corundum was attributed to the higher capacitance (due to higher r of corundum), reduced impedance and increased power in the DBD. Ozkan et al 27 also studied the effect of relative permittivity on the discharge mode and CO 2 conversion in a tubular flowing DBD. They however did not observe any linear trend of increased conversion with increasing relative permittivity of the dielectric materials.…”

Effects of discharge parameters on carbon dioxide conversion in TiO2 packed dielectric barrier discharge at atmospheric pressure

“…The highest energy efficiency 15.80% is achieved at the Clearly, a trade-off effect exists between the conversion of CO 2 and efficiency of the plasma process [10]. Therefore, in order to enhance conversion and energy efficiency, other parameters and methods like bead size [19], synergy of plasma-catalysis [9], dilution of gas [20,21] and barrier thickness [22] could be taken into account. Then the frequency is fixed at 8.06 kHz, and the flow rate is changed from 15 ml/min to 45 ml/min.…”