Browsing by Author "Hung, C. -T."

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A parallel hybrid numerical algorithm for simulating gas flow and gas discharge of an atmospheric-pressure plasma jet
(2012-12-01)
Lin, K. -M.
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Hu, M. -H.
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Hung, C. -T.
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Wu, J. -S.
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Hwang, F. -N.
Development of a hybrid numerical algorithm which couples weakly with the gas flow model (GFM) and the plasma fluid model (PFM) for simulating an atmospheric-pressure plasma jet (APPJ) and its acceleration by two approaches is presented. The weak coupling between gas flow and discharge is introduced by transferring between the results obtained from the steady-state solution of the GFM and cycle-averaged solution of the PFM respectively. Approaches of reducing the overall runtime include parallel computing of the GFM and the PFM solvers, and employing a temporal multi-scale method (TMSM) for PFM. Parallel computing of both solvers is realized using the domain decomposition method with the message passing interface (MPI) on distributed-memory machines. The TMSM considers only chemical reactions by ignoring the transport terms when integrating temporally the continuity equations of heavy species at each time step, and then the transport terms are restored only at an interval of time marching steps. The total reduction of runtime is 47% by applying the TMSM to the APPJ example presented in this study. Application of the proposed hybrid algorithm is demonstrated by simulating a parallel-plate helium APPJ impinging onto a substrate, which the cycle-averaged properties of the 200th cycle are presented. The distribution patterns of species densities are strongly correlated by the background gas flow pattern, which shows that consideration of gas flow in APPJ simulations is critical. (C) 2012 Elsevier B.V. All rights reserved.
Development of an improved spatial reconstruction technique for the HLL method and its applications
(2011-02-01)
Smith, Matthew R.
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Lin, K. -M.
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Hung, C. -T.
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Chen, Y. -S.
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Wu, J. -S.
The integral form of the conventional HLL fluxes are presented by taking integrals around the control volume centred on each cell interface. These integrals are demonstrated to reduce to the conventional HLL flux through simplification by assuming spatially constant conserved properties. The integral flux expressions are then modified by permitting the analytical inclusion of spatially linearly varying conserved quantities. The newly obtained fluxes (which are named HLLG fluxes for clarification, where G stands for gradient inclusion) demonstrate that conventional reconstructions at cell interfaces are invalid and can produce unstable results when applied to conventional HLL schemes. The HLLG method is then applied to the solution of the Euler Equations and Shallow Water Equations for various common benchmark problems and finally applied to a 1D fluid modeling for an argon RF discharge at low pressure. Results show that the correct inclusion of flow gradients is shown to demonstrate superior transient behavior when compared to the existing HLL solver and conventional spatial reconstruction without significantly increasing computational expense. (C) 2010 Elsevier Inc. All rights reserved.
Effect of free electrons on nanoparticle charging in a negative direct current corona charger
(2008-10-13)
Aliat, A.
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Tsai, C. -J.
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Hung, C. -T.
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Wu, J. -S.
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機械工程學系
A two-dimensional numerical model is proposed in this letter to take into account the effects of free electrons on nanoparticle charging in a negative direct current wire-tube corona charger. Numerical results are in excellent agreement with the experimental data by using a capturing probability of electrons onto nanoparticles with a value of 0.013. These free electrons contribute greatly to the charging efficiency at high products of mean ion concentration and mean residence time, which explains very well the large discrepancy found in earlier models that considered only negative ions. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2967470]
Investigation of the Atmospheric Helium Dielectric Barrier Discharge Driven by a Realistic Distorted-Sinusoidal Voltage Power Source
(2011-02-01)
Hung, C. -T.
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Chiu, Y. -M.
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Hwang, F. -N.
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Chiang, M. -H.
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Wu, J. -S.
The non-equilibrium atmospheric-pressure parallel-plate helium dielectric barrier discharge (DBD) driven by a realistic 20 kHz distorted-sinusoidal voltage waveform has been investigated by means of simulations and experiments. A self-consistent one-dimensional fluid modeling code considering the non-local electron energy balance was applied to simulate the helium DBD. The effect of selecting plasma chemistry was investigated by comparing simulations with experiments. The results show that the simulations, which include more excited helium, metastable helium and electron-ion-related reaction channels, can faithfully reproduce the measured discharged temporal current quantitatively. Based on the simulated discharge properties, we have found that there is complicated mode transition of discharges from the long Townsend-like to the "dark current"-like, then to the short primary Townsend-like and the short secondary Townsend-like for the helium DBD that is driven by a realistic distorted-sinusoidal voltage power source. Discharge properties in different periods of discharge are discussed in detail in the paper.
Numerical Investigation of a Parallel-Plate Atmospheric-Pressure Nitrogen/Ammonia Dielectric Barrier Discharge
(2012-06-01)
Li, F. -L.
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Lin, K. -M.
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Yang, Y. -W.
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Hung, C. -T.
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Wu, J. -S.
In this paper, a planar atmospheric-pressure dielectric barrier discharge (AP-DBD) of nitrogen mixed with ammonia (0-2 %) is simulated using one-dimensional self-consistent fluid modeling with cell-centered finite-volume method. This AP-DBD is driven by a 30 kHz power source with distorted sinusoidal voltages. The simulated discharge current densities are found to be in good agreement with the experiment data in both phase and magnitude. The simulated results show that the discharges of N-2 mixed with NH3 (0-2 %) are all typical Townsend-like discharges because the ions always outnumber the electrons very much which leads to no quasi-neutral region in the gap throughout the cycle. N-2 (+) and N-4 (+) are found to be the most abundant charged species during and after the breakdown process, respectively, like a pure nitrogen DBD. NH4 (+) increases rapidly initially with increasing addition of NH3 and levels off eventually. In addition, N is the most dominant neutral species, except the background species, N-2 and NH3, and NH2 and H are the second dominant species, which increase with increasing added NH3. The existence of abundant NH2 plays an important role in those applications which require functional group incorporation.
Simulation of Excimer Ultraviolet (EUV) Emission from a Coaxial Xenon Excimer Ultraviolet Lamp Driven by Distorted Bipolar Square Voltages
(2010-12-01)
Jou, S. -Y.
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Hung, C. -T.
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Chiu, Y. -M.
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Wu, J. -S.
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Wei, B. -Y.
Simulation of excimer ultraviolet (EUV) emission from a coaxial xenon excimer ultraviolet lamp driven by distorted bipolar square voltages is presented in this study. A self-consistent radial one-dimensional fluid model, considering local mean energy approximation (LMEA), along with a set of simplified xenon plasma chemistry was employed to simulate the discharge physics and chemistry. Emitted powers of EUV light and deposited powers to the charged species were simulated by varying the values of four key parameters, which include the driving frequency, gas pressure, gap distance and number of dielectric layers. Results show that there are three distinct periods that include pre-discharge, discharge and post-discharge ones. It is found that intensive EUV (172 nm) emission occurs during the early part of the discharge period, which correlates very well in time with the power deposition through electrons. In addition, power deposition through Xe(+) and Xe(2)(+) occurs mainly in the discharge period and later part of discharge period, respectively. Surprisingly, the emission efficiency of 172 nm increases slightly with increasing driving frequency of power source, while it increases dramatically with increasing gap distance. In addition, the maximal emission efficiency is found to take place at gas pressure of 600 torr. The emission efficiency of one-dielectric case is found to be better than that of two-dielectric one. The underlying mechanisms in the above observations are discussed in detail in the paper.