Bijan Pashaie

Non‐thermal plasma remediation of SO2/NO using a dielectric‐barrier discharge

Here we report the experimental and simulation results of removal of SO2 and NO from a simulated coal combustion gas using a dielectric‐barrier discharge. A Monte Carlo calculation is done to determine the transport properties of the flue gas. Following this, a detailed plasma chemistry calculation is done which takes into account the pulsed nature of the dielectric‐barrier discharge. The computed results are in good agreement with the experimental data. We find that in low concentrations (400 ppm for SO2 and 100 ppm for NO) the dielectric‐barrier discharge was capable of removing 99% of the SO2 and NO. Due to temperature dependence of the heavy particle reactions, there is a decrease in NO removal as the energy density is increased past an optimum value.

Streamer discharge simulation in flue gas

Streamer discharges are formed in a dielectric-barrier discharge used for nonthermal plasma generation. The results of simulation of streamer type discharge in a flue gas mixture is reported. A Monte Carlo simulation is done to obtain the transport and appropriate rate coefficients. The transport and rate coefficients calculated from the Monte Carlo is used to solve the conservation equations for electron, positive and negative ions, together with the Poissons equation. The G-factor (radicals produced per 100 eV of electrical energy input to the discharge) obtained for Townsend-type discharge is higher as compared to a streamer-type discharge. Also experimental results of the SO/sub 2/ removal efficiency is compared to theoretical predictions. >

Electrical characteristics of a coaxial dielectric barrier discharge

The dielectric barrier is becoming popular as a source of atmospheric pressure non-thermal plasmas. For atmospheric pressure plasma processing, either coaxial or parallel plate geometry can be used. In this paper, experimental investigation of the electrical characteristics of a coaxial dielectric barrier discharge is reported. The ratio of the inner to outer electrode radius has large influence on the corona onset voltage and the generation of radicals. It was also found that low levels of ultraviolet irradiation increase the number of microdischarges considerably resulting in a more uniform discharge. Also the energy coupled to the discharge from the power source increases with ultraviolet irradiation.

Laser-induced fluorescence of OH radicals in a dielectric barrier discharge

We discuss the results of laser-induced fluorescence measurements of OH radicals in a dielectric-barrier discharge. The discharge is in parallel plate geometry in atmospheric pressure air and argon. Although the air discharge consists of discrete microdischarges, two-dimensional images show the spatial uniformity of the OH radical. Results show that with increasing power, the OH production decreases due to gas heating and increased ozone production. The addition of O2 increases the OH production at low concentrations; however, at higher O2 concentration the OH concentration decreases due to increased electron attachment.

Characteristics of a barrier discharge in monatomic and molecular gases

We show that, in a parallel-plate dielectric-barrier discharge, monatomic gases behave very differently from molecular gases. Time-resolved images show diffused discharge for monatomic gases and filamentary discharge for molecular gases. In addition, current waveforms also show a marked difference. An empirical relationship for power and voltage is derived which shows good agreement with experimental results for both monatomic and molecular gases.

rf-generated ambient-afterglow plasma

Atmospheric pressure plasmas have gained importance due to their potential application in polymer surface treatment, surface cleaning of metals, thin film deposition, and destruction of biological hazards. In this paper a radio-frequency driven atmospheric pressure afterglow plasma source in argon and helium is discussed. The light intensity measurement shows that the radio-frequency discharge is continuous in time unlike the intermittent nature of a low frequency dielectric-barrier discharge. The discharge, under ambient conditions, can be generated in argon, helium, and nitrogen. Spectroscopic measurements show that metastables are capable of producing oxygen atoms and other excited species. The argon afterglow, in particular, is capable of dissociating oxygen molecules in the ambient gas. An afterglow model has been developed to study the interaction of the plasma with the ambient gas. Results from applications of the plasma to surface treatment of metals and polymers, and bacterial decontamination are briefly discussed.

Characteristics of a barrier discharge in monatomic gases

Summary form only given. Experiments in a simple parallel-plate dielectric-barrier discharge show that the structure of monatomic gases is very differently from molecular gases. Time-resolved images show diffused discharge for monatomic gases and filamentary discharge for molecular gases. In addition, current waveforms also show a marked difference. Two-dimensional streamer calculation show that in a monatomic gas the discharge is diffused compared to molecular gases. The high ionization coefficient at low reduced field, the high diffusion constant and the high secondary ionization coefficient of monatomic gases can account for these differences. Also an empirical relationship for power and voltage is derived which shows good agreement with experimental results for both monatomic and molecular gases.

Laser induced fluorescence spectroscopy of OH radicals in an atmospheric pressure discharge

Summary form only given, as follows. Laser induced fluorescence (LIF) spectroscopy is used to study the temporal and spatial evolution of OH radicals in atmospheric pressure dielectric-barrier-discharge in air. A Nd:YAG pumped dye laser with wavelength doubler is used to generate the excitation wavelength in the 282 nm range. The laser is tuned to the Q(0,0) resonance of OH and a broadband detection is done of the Q(0,1) manifold. An image intensified CCD camera is used to record the fluorescence along with a narrow-band spectral filter. The discharge is operated at atmospheric pressure in air. The discharge configuration is planer with a single dielectric inserted between electrodes. Measurements of OH concentration with respect to the excitation voltage will be reported. Also spatial measurements of OH concentration in the gap will be reported.