Modelling of a CO2-N2 Plasma Flow in a Supersonic Arcjet Facility

Abstract

The Martian-type CO 2 -N 2 plasma flow obtained in the plasma generator of the SR5 arcjet facility has been simulated using two complementary fluid descriptions. An inviscid multitemperature monofluid description has firstly been used to evaluate the importance of the different chemical and exchange processes between the flow species. Then, a one-temperature Navier-Stokes description has been used to evaluate the influence of viscous and rarefaction effects. In the nozzle throat region, heat addition from the arc firstly leads to the establishment of a translation-vibration disequilibrium. Near the end of the nozzle throat, temperature and pressure increases allow more efficient exchange processes and lower this disequilibrium. In the nozzle diverging region, chemical and vibrational processes are quickly frozen as the flow strongly expands. Furthermore, a translation-rotation disequilibrium also occurs near the nozzle exit. Navier-Stokes simulation results evidence a quick increase of the diverging section boundary layers, and therefore most of the diverging section is in a fully viscous interaction regime. Moreover, rarefaction effects are predicted to appear near the nozzle exit walls. The experimental measurements carried near the nozzle exit confirm the thermal disequilibrium regime of the flow, predicted by the simulation results. Nomenclature anode = nozzle anode arc = nozzle electrical arc cathode = nozzle cathode chamber = facility vacuum chamber Da = Damköler number gas = facility gas flow generator = conditions upstream of the nozzle throat h = flow enthalpy, MJ=kg i = chemical species index Kn = Knudsen number k B = Boltzmann constant, 1:38065 10 23 J=K L = characteristic length, m M = flow Mach number _ m = mass flow, kg=s _ Q = heat transfer rate, kJ=s p = flow pressure, Pa R-T = rotation-translation processes T = flow translational temperature, K T rot = species rotational temperature, K T vib = species vibrational temperature, K T w = nozzle wall temperature, K V-D = vibration-dissociation processes V-el = vibration-electron processes V-T = vibration-translation processes V-V = vibration-vibration processes v = flow velocity, m=s ZT; T vib = nonequilibrium coupling factor for dissociation Z 1 = Parker rotational collision number E = energy transfer rate, kW = arc energy transfer efficiency = flow density, kg=m 3 = collisional cross-section, m 2 F = flow characteristic time, s vib = vibrational relaxation characteristic time, s

Kinetic Description of Martian Atmospheric Entry Plasma

“…We start with an assumed electron density and then calculate N ik from (9). Then, we apply (10) to recalculate the electron density and repeat this process.…”

“…where [X] is the concentration of species X, [CO 2 ] o is the initial concentration of neutral CO 2 , k n is the rate coefficient for nth reaction, and N e is the electron density calculated from (9). Equations (15) and (16) represent the mass conservation of carbon and oxygen atoms in the plasma, respectively.…”

“…Although we have considered that the plasma formed during atmospheric entry will be in thermal equilibrium with the gas temperature (T e ∼ T g ), there have been many recent papers discussing the possibility that it is nonthermal equilibrium plasma [6], [9], [10]. As such, for a first approximation, we have set T e = 2 * T g and T e = 1/2 * T g in our model to determine the effect this will have on the electron density.…”

Metastable oxygen atom velocity and temperature in supersonic CO2plasma expansions

“…A recorded spectral profile is a direct measurement of the local metastable oxygen atom FDV. Stark and pressure broadening can be neglected in view of, respectively, the low electron density [16] 3 and the low gas pressure [17]. Moreover, the laser power deposited inside the measurement volume was kept below 3 mW to limit power broadening [18].…”

Effects of copper vapour on thermophysical properties of CO2-N2 plasma

“…Martian and Venusian atmospheres), the high-temperature CO 2 -N 2 mixtures have been studied for their thermodynamic and transport properties since 1960s [1,2]. Even recently, the research on CO 2 -N 2 plasma can be found for thermophysics and hydrodynamics [3][4][5][6][7][8]. In industries, due to the high global warming potential (GWP) of SF 6 (24 000 times higher than that of CO 2 [9]), CO 2 and N 2 are also applied to replace SF 6 and reduce GWP, for example, as insulating medium in gas-insulated switchgears (GIS) [10] and as arc quenching medium in gas circuit breakers (GCB) [11].…”