Browsing by Author "Lin, K-M"

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A temporal multi-scale algorithm for efficient fluid modeling of a one-dimensional gas discharge
(2014-12-01)
Gu, B-R
;
Lin, K-M
;
Hu, M-H
;
Hung, C-T
;
Wu, J-S
In this study, we present a temporal multi-scale algorithm (TMA) for efficient fluid modeling of a one-dimensional gas discharge with complex plasma chemistry. A helium dielectric barrier discharge driven by a power source with a frequency of 25 kHz is used as an example to demonstrate the superior capability of the TMA in accelerating fluid modeling simulations, while maintaining the same accuracy as compared to lengthy benchmarking fluid modeling using a single time-scale approach. The plasma chemistry considers 36 species and 121 reaction channels, which include some impurities such as nitrogen (25 ppm), oxygen (10 ppm) and water vapor (1 ppm), in addition to the helium itself. The results show that the runtime using the TMA can be dramatically reduced to 4% (25 times faster) with a relative difference of spatially averaged number densities generally less than 1% for all species between the TMA and the benchmarking cases when five initial cycles, five supplementary cycles and four repeated stages are used. Further reduction of the accuracy requirements to 44% for some specific species can lead to 92 times faster performance with the use of two initial cycles, two supplementary cycles and two repeated stages. The outlook for multi-dimensional fluid modeling considering a gas flow field is also described at the end of the paper.
Numerical and experimental investigation of light emissions of a planar nitrogen atmospheric-pressure dielectric barrier discharge due to addition of ammonia considering oxygen impurity
(2013-12-01)
Li, F-L
;
Hung, C-T
;
Lin, K-M
;
Wei, T-C
;
Wu, J-S
In this paper, the mechanisms of light emissions, including NO-gamma, NO-beta and N-2-SPS, produced in a N-2/NH3 atmospheric-pressure dielectric barrier discharge considering realistic oxygen impurity (30 ppm) are investigated numerically and experimentally. Self-consistent, one-dimensional fluid modeling is used to numerically simulate the discharge process with 48 species and 235 reaction channels. An optical emission spectrometer (OES) is used to measure the relative intensities of the light emission. The simulations of the light emission intensities for the above-mentioned OES lines generally reproduce the trends observed in the experiments caused by changes in the NH3 concentration. All of the predicted intensities of NO-gamma, NO-beta and N-2-SPS decrease with increasing amount of NH3 caused by various reaction mechanisms. The former is due to the loss of N-2(A) and NO(A) by the reaction of NH3 with N-2(A) and NO(A), respectively. The decrease in NO-beta is due to the depletion of N and O because of NH3, and the decrease in N-2-SPS is due to electron attachment to NH3 and a weaker metastable-metastable associative ionization of N-2. All of the simulated results demonstrate that the discharges are typically Townsend-like because the ions outnumber the electrons and the electric field across the gap is distorted only slightly by the charged particles during the breakdown. Finally, a reduced chemical kinetics model for a planar atmospheric-pressure N-2/O-2/NH3 dielectric barrier discharge is proposed and validated by benchmarking against the above complete chemical kinetics. This results in a reduced chemical kinetics consisting of 33 species and 87 reactions with a very limited loss of accuracy of discharge properties, while it is 2.1 times faster in computational time as compared with the complete version.