Pulsed Electric Discharge Research Articles

Aerodynamic Modification of Supersonic Flow Around Truncated Cone Using a Pulsed Electrical Discharges

An experimental study on the use of plasma to improve blunt body aerodynamics in a supersonic flow is presented. Shadow, schlieren, and plasma glow imaging techniques were used simultaneously for flow and plasma visualization. The discharge current and voltage, as well as the flow pressure and temperature at different locations on the surface of the model, were measured. With a proper aspect ratio 0.81 of the physical spike length to the frontal diameter of a 60-deg truncated cone-cylinder designed for the wind-tunnel model, the on-board pulsed electrical discharge produced a conically distributed plasma around the cathode, which modified the main shock wave structure from a detached bow shock to a tip attached conical shock wave

Macroscopic separation of charges in a pulsed electric discharge

The possibility of separating charges in an ordinary electric discharge was demonstrated. The luminous object formed after the end of the discharge was found to exist over a few hundred milliseconds, or six orders of magnitude longer than the lifetime of an ideal plasma of the same volume. It is shown that the luminous object has a negative electric charge and has no free charged particles of opposite sign.

Hydrogen, Oxygen, and Hydrogen Peroxide Formation in Aqueous Phase Pulsed Corona Electrical Discharge

High voltage electrical discharges in water are of increasing interest for the degradation of organic compounds and destruction of biological species. The present study reports measurements of the rates of molecular hydrogen, molecular oxygen, and hydrogen peroxide formation in a pulsed positive needle-plane corona-like electrical discharge in water. In experiments for various solution conductivities, applied voltages, and discharge powers, the ratio of the molar rate of production of hydrogen:hydrogen peroxide:oxygen was approximately 4:2:1. The highest observed rate of hydrogen production was 1.3 μmol/s at discharge power of 37 W (or 0.25 g of H2/kW·h) at solution conductivity 50 μS/cm. The G-value for hydrogen production was 0.17 molecule of H2/100 eV, falling in the range of that found in the radiation chemistry literature (∼0−0.5 molecule of H2/100 eV, depending on scavenger concentration). A global reaction is proposed to add to existing kinetic models for the simulation of reactive species producti...

Exhaustion of a Low-Temperature Plasma Jet Formed by an Electric Discharge from a Semi-Closed Volume

The motion of a gas medium formed by water evaporation under the action of a high-power pulsed electric discharge in a cylindrical semi-closed volume and exhausting into the ambient space is numerically examined. A significant effect of chemical reactions on the flow structure is demonstrated.

Vapor condensation study for HIF liquid chambers

This paper presents the experimental study of transient cooling and condensation of the prototypical material flibe under conditions relevant to Heavy Ion Fusion (HIF) power plants. Superheated vapor is generated by a high-current, pulsed electrical discharge over a pool of liquid flibe. The excited vapor expands inside a temperature-controlled chamber designed to scale the initial density of the generated vapor, the initial energy density and the surface area available for condensation, considering HYLIFE-II as the reference design. Clearing rates are evaluated from the measured pressure history. Mass spectroscopy is used to characterize the composition of the residual gases. SEM analysis of material deposited on witness plates is also presented, showing that interface phenomena during the initial expansion phase depend on the orientation of the condensation surface relative to the gas velocity. The results show that chamber clearing can be characterized by an exponential decay with a time constant of 6.58 ms. However, the equilibrium pressure is one order of magnitude higher than the desired HIF base pressure because of the presence of non-condensable impurities dissolved in the material available for the experiments. If the exponential decay is applied to the pressure range of the reference design, the resulting period for chamber clearing is 60 ms. The conclusion is that condensation rates of flibe vapor are sufficiently fast to allow HIF power plants repetition rates, and that the main issue for flibe vapor condensation lies in the control of the impurities dissolved in the salt.

Infrared absorption spectroscopy of diacetylene ions trapped in solid argon

The C4H2+ diacetylene radical cation has been generated in a pulsed jet electrical discharge through both a diacetylene/argon mixture and an acetylene/argon mixture. The product mixture was trapped on a 12 K cryostat window and studied via Fourier transform infrared absorption spectroscopy. The diacetylene cation was also produced via low energy electron bombardment of an effusive C4H2/Ar beam. Two new infrared bands at 3201.6 and 1827.9 cm(-1) have been identified as vibrations of the diacetylene cation, viz the v4 (sigmau) (C-H stretching) and the v5(sigmau) (C[triple bond]C stretching) modes, respectively. Geometry optimization and harmonic frequency calculations, carried out at various spin unrestricted levels (B3LYP, CCSD(T)) for spin doublet structures, indicate that, in its electronic ground state X2pi(g), the C4H2+ cation is linear. Three additional new bands at 2957.5, 1693.8 and 594.5 cm(-1) have been tentatively assigned to the C-H stretching, C[triple bond]C stretching and C[triple bond]C-H (in-plane) bending modes, respectively, of the nonlinear diacetylene anion (C4H2-, X2B(u)).

Plasma supported combustion

Oxidation of molecular hydrogen and different hydrocarbons in stoichiometric mixtures with air and oxygen in the pulsed nanosecond discharges was studied at room temperature, and the detailed kinetics of the process has been numerically investigated. In the discharge afterglow, the reactions including electron-excited particles play a dominant role for the time up to 100 ns, ion–molecular reactions—for the time of microsecond range, and reactions including radicals mostly contribute for the time interval of several milliseconds. The principal role of processes with formation of excited components that support the development of the chain mechanism of oxidation has been shown. The spatial uniformity of the gas-mixture combustion initiated by a high-voltage nanosecond volume discharge is investigated at gas pressures of 0.3–2.4 atm and temperatures of 1000–2250 K. The self-ignition time and the time of discharge-induced ignition are determined. It is found that the discharge significantly (by 600 K) decreases the ignition temperature with very low energy in the discharge (∼10 −2 J/cm 3). The influence of gas excitation by a pulsed nanosecond discharge with a high-voltage pulse amplitude up to 25 kV on the properties of a premixed propane–air flame has been investigated over a wide range of the equivalence ratios (0.4–5). It was experimentally found that the flame’s blow-off velocity increased more than twice at a discharge energy input less than 1% of the burner power. Efficient production of active radicals under the action of a barrier discharge has been observed. The increase in the flame’s propagation velocity is explained by the production of atomic oxygen in a discharge by the quenching of electronically excited molecular nitrogen N 2 and the dissociation of molecular oxygen on electron-impact. A numerical model has been developed, which describes the influence of pulsed electric discharges on the ignition, combustion, and flame propagation.

Removal of pollutants by plasma catalytic processes

Removal of molecular atmospheric pollutants by non-thermal plasmas is under study since the beginning of the eighties. It has been shown that pulsed electrical discharges, such as dielectric barrier or corona discharges, are powerful means to eliminate Volatile Organic Compounds (VOCs) from the ambient air, or to treat flue gases which contain nitrogen oxide. However it is now recognised that, for several pollutants, the use of the plasma alone does not allow a complete elimination of the undesirable molecule. For example NO is oxidised in the air plasma to form other oxides like NO 2 and N 2 O 5 , and reactions of oxygen atoms or hydroxyl radicals produced by the discharge with VOCs can lead not only to H 2 O and CO 2 but to a number of by-products following the partial oxidation of the molecule, which can be as undesirable than the compound to be initially removed from effluents. This is particularly the case when the electrical energy deposited in the gas flow must be kept as low as possible in order to design a low energy cost equipment. As a result addition of a catalyst together with the pulsed discharge is now investigated in various laboratories in order to achieve a complete oxidation of VOCs, i.e. the so-called de-COV process, or a complete reduction of NO X (NO and NO to produce N 2 and O 2 , i.e. the so-called de-NO X process, at low energy consumption. This paper is a short review of works which have been done these last years in that domain, specifically on NO X and some selected VOC molecules.

Free internal rotation in CH 3–C [tbnd]C–CF 3

The molecular beam Fourier transform microwave spectrum in the ground vibrational state of the symmetric rotor CH 3–C C–CF 3 has been detected and analyzed in the frequency interval 6–18 GHz. The molecule was generated in a pulsed dc electric discharge of trifluoropropyne and propyne seeded in neon. The observed spectrum exhibits a complex pattern of lines for each rotational transition consistent with free internal rotation of the two tops. The rotational parameters B, D J , D Jm , D JK , D JKm and H Jm have been determined from the fit of the observed lines.

Phosphorus hyperfine structure in the electronic spectrum of the HPCl free radical.

The 444 nm 2 0 (1) bands of the A 2A'-X 2A" transition of the jet-cooled HP 35Cl and HP 37Cl radicals have been studied at high resolution using the pulsed electric discharge technique with a precursor mixture of PCl3 and H2. Spectra recorded with linewidths of approximately 360 MHz revealed resolved hyperfine structure in both isotopomers arising from the excited state Fermi contact interaction of the unpaired electron with the magnetic moment of the 31P nucleus, with aF'=0.0641(10) cm(-1) and 0.0636(31) cm(-1) for HP 35Cl and HP 37Cl, respectively. No contribution from the ground state, or excited state contributions from the hydrogen or chlorine nuclei were resolved, confirming ab initio predictions that HPCl is a p pi radical in the X state, and an s sigma radical with a substantial contribution from the phosphorus 3s atomic orbital in the A state. The free atom comparison method has been used to estimate that the singly occupied molecular orbital in the excited state has 14% phosphorus 3s character.

The Removal of Direct Orange 39 by Pulsed Corona Discharge From Model Wastewater

Untreated wastewater from the dye industry and dyehouses cannot be directly discharged into the environment due to the high content of organic matter and intensive colouration, even with low concentrations of dye. In this paper, the application of a high voltage pulsed electrical discharge in the aqueous phase has been assessed for the dye degradation. Experiments were conducted in a batch reactor using model wastewater of the commercial water-soluble monoazo dye C.I. Direct Orange 39 (DO39). The effects of zeolite and ferrous sulphate in combination with the corona discharge were examined. Experiments were conducted for a range of process parameters including pH, conductivity, type and amount of zeolite, and ferrous sulphate concentration. A mathematical model to describe the kinetics of DO39 degradation in the corona reactor was developed. Aqueous phase pulsed streamer corona discharge as a method for coloured wastewater treatment showed very high effectiveness in the case of iron salt addition (Fenton's reaction). Low pH enhanced dye removal by corona in the absence of zeolite, thus implying that the acid properties of zeolites are important in dye degradation. Ecological parameters such as COD, TC, IC, TOC and IC50 measured before and after corona treatment showed that the treated wastewater can be discharged into the environment or reused as process water.

Organic synthetic dye degradation by modified pinhole discharge

The aim of this work was to investigate the possibility of applying a high voltage pulsed electrical discharges for dye wastewater treatment. Commercial organic monochlorotriazine reactive dye of the anthraquinone type C.I. Reactive Blue 49 (RB49) was chosen as a representative of persistent and recalcitrant wastewater pollutant. The modified pinhole discharge flow-through reactor was used to treat such type of contaminant. Applying HV pulses 30 kV, 3.15 J/pulse, 50 Hz repetition rate, complete decolorisation and partial mineralization of RB49 has been reached and demonstrated by means of UV/VIS absorption, TOC and AOX measurements.

Persistence rewarded: successful observation of the B 2Sigmau+-X 2Pig electronic transition of jet-cooled BS2.

The B-X electronic transition of jet-cooled BS2 has been observed using laser-induced fluorescence techniques. The boron disulfide radical was produced in a pulsed electric discharge jet using a mixture of BCl3 and CS2 in high-pressure argon as the precursor. The spectrum consists of a strong 0(0)(0) band with the 2Sigma-2Pi(3/2) component at 24,393.2 cm(-1) and short progressions in the symmetric stretching (nu1' = 506.7 cm(-1)) and bending (nu2' = 303.2 cm(-1)) modes. A rotational analysis of both spin-orbit components of the 0(0)(0) band gave an upper state B value of 0.0932779(19) cm(-1) and a ground-state spin-orbit coupling constant of A = -405.163(4) cm(-1). The ground-state bond length of 1.66492 angstroms increases to 1.6812(1) angstroms on sigmau --> pig electronic excitation. The B-X data have been used to further refine the Renner-Teller analysis, which is in good agreement with our previous work [J. Chem. Phys. 119, 2047 (2003)].

Propagation of an Electric Discharge over the Surface of Water and Semiconductor

The propagation of a series of pulsed electrical discharges is investigated over the free surface of water, along a water-saturated porous polymer, over a thin water jet, and over the surface of a semiconductor. It is found that the length of a surface discharge may be several times the limit size of the breakdown gap in air and, in a wide range of variation of parameters, is independent of the electrical conductivity of water. The relay mechanism of propagation of such a discharge is revealed. The mechanisms of the formation of droplets during a discharge are analyzed.

The Renner-Teller effect and Sears resonances in the ground state of the GeCH and GeCD free radicals

The vibrational energy levels of the jet-cooled GeCH and GeCD radicals have been studied by a combination of laser-induced fluorescence and wavelength-resolved emission techniques. The radicals were produced in a pulsed electric discharge free jet expansion using methyltrichlorogermane and tetramethylgermane-d12 precursors. A re-examination of the weaker hot bands in the LIF spectrum has provided a more complete vibrational analysis of the upper state energy levels. The single vibronic level emission spectra obtained by pumping several bands of each isotopomer were analyzed to provide information on the low-lying ground state vibronic energy levels up to 3000 cm−1 above the zero-point level. Strong interactions occur in these molecules between vibronic levels with the same value of P, but differing by one unit of v2; such interactions were first described for NCS by Northrup and Sears [Mol. Phys. 71, 45 (1990)] and are conveniently called “Sears resonances.” The spectra of GeCH were further complicated by Fermi resonances between the bending and Ge–C stretching levels. Despite these difficulties, it proved possible to analyze the data using a standard Renner-Teller model with the addition of Sears resonance coupling terms. The validity of the fitted parameters was tested using the isotope relations. The Sears resonance parameters for GeCH are much larger than those of NCS, a result of the much stronger vibronic coupling in the germanium methylidynes.

A highly intense state-selected OH beam source by the pulsed electric DC discharge method

A high intensity pulsed DC discharge source for OH radical beam was developed by the systematic optimization for geometry of the discharge source and for the operation conditions. OH radicals produced in the DC discharge source were state-selected by an electrostatic hexapole field. The maximum OH flux in the lowest | J, Ω, M〉=|3/2,3/2,3/2〉 state was directly measured to be 8.5 × 10 14 radicals cm −2 s −1 at the beam crossing point of 150 cm downstream from nozzle by a saturated laser-induced fluorescence spectroscopy for the Q 1(1) transition in A 2Σ←X 2Π 3/2 transition.

Raman study of aqueous sodium nitrate, activated by the high-voltage pulsed electric discharge

Raman spectra of a saturated aqueous solution of sodium nitrate (NaNO 3/H 2O) in the region of the totally symmetric vibration ν 1( A) of the NO 3 − anion has been studied. The high-voltage pulsed electric discharge effect (HPED activation) on the molecular relaxation in NaNO 3/H 2O has been investigated. The temperature dependences of the width and frequency of the corresponding spectral line are examined. The transition of NaNO 3/H 2O from the normal state to the activated state under HPED effect is observed. The activated state of NaNO 3/H 2O is nonequilibrium and metastable.

A study of the molecular structure and Renner–Teller effect in the à 2Πu–X̃ 2Πg electronic spectrum of jet-cooled boron disulfide, BS2

The à 2Πu–X̃ 2Πg electronic band system of jet-cooled boron disulfide (BS2) has been recorded in the 760–530 nm region by laser-induced fluorescence (LIF) and wavelength resolved emission techniques. The free radical was produced in a pulsed electric discharge jet using a precursor mixture of BCl3 and CS2 in argon. The LIF spectrum consists of a long progression of strong bands involving the ν1′ (B–S stretching) mode and combinations involving 2ν2′ and 2ν3′, as well as many hot bands built on the 211 band. Detailed analysis of the spectrum shows that the ground state exhibits a substantial Renner–Teller effect with ε=−0.2012 and a spin–orbit coupling constant of A=−413.80 cm−1. Angular momentum coupling is negligible in the excited state, which has a much smaller spin–orbit coupling constant of A=−259.15 cm−1. The vibrational frequencies of BS211 are ω1″=542.8, ω2″=285.0, ω3″=1010.5, ω1′=514.1, ω2′=309.7, and ω3′=1543.6 cm−1. Rotational analysis of the 000 band allowed a determination of the effective molecular structures as r0″(BS)=1.6648(4) Å and r0′(BS)=1.7127(5) Å. Ab initio methods have been used to predict the BS2 spectroscopic parameters and good agreement with experiment was found. Our present understanding of the LIF spectrum is in accord with the pioneering analysis of the absorption spectrum of matrix isolated BS2 published by Brom and Weltner [J. Mol. Spectrosc. 45, 82 (1973)] three decades ago.

The electronic spectroscopy and molecular structure of the HPCl free radical: A potential III–V semiconductor growth intermediate

The à 2A′–X̃ 2A″ electronic spectra of jet-cooled HPCl and DPCl have been obtained for the first time using the pulsed electric discharge technique with a precursor mixture of PCl3 and H2 or D2. From a combination of laser-induced fluorescence and wavelength resolved emission spectra, all of the vibrational frequencies in the ground and excited states of both isotopomers have been measured and vibrational force fields have been determined. Rotational analyses of the 000 bands of both isotopomers showed small doublet splittings characteristic of an asymmetric top molecule with a single unpaired electron. From the rotational constants and the force fields, estimated equilibrium structures were derived with r″(PH)=1.4158(23) Å, r″(PCl)=2.0388(23) Å, θ″=95.02(27)°, and r′(PH)=1.4067(20) Å, r′(PCl)=2.0050(2) Å, and θ′=115.53(12)°. The experimental data firmly establish that the observed spectra and those previously obtained by chemiluminescence techniques [Bramwell et al., Chem. Phys. Lett. 331, 483 (2000)] are due to the HPCl free radical.

Getting a charge out of water

This article reports on research for an electrical alternative to chemical disinfection as disinfection byproducts of chlorine come under increasing scrutiny by European Community health agencies. The research involves a pulsed electric arc discharge in water where high‐voltage arcing between submerged electrodes created countless free radicals that can cause chain reactions in the water to destroy pathogens, other contaminants, and polluting molecules. The system is based on a cylindrical vessel in which an electric arc is passed between two rod‐type electrodes at high voltage.