Ksc Kim Peerenboom

Mass conservative finite volume discretization of the continuity equations in multi-component mixtures

The Stefan-Maxwell equations for multi-component diffusion result in a system of coupled continuity equations for all species in the mixture. We use a generalization of the exponential scheme to discretize this system of continuity equations with the finite volume method. The system of continuity equations in this work is obtained from a non-singular formulation of the Stefan-Maxwell equations, where the mass constraint is not applied explicitly. Instead, all mass fractions are treated as independent unknowns and the constraint is a result of the continuity equations, the boundary conditions, the diffusion algorithm and the discretization scheme. We prove that with the generalized exponential scheme, the mass constraint can be satisfied exactly, although it is not explicitly applied. A test model from the literature is used to verify the correct behavior of the scheme.

Integral simulation of the creation and expansion of a transonic argon plasma

A transonic argon plasma is studied in an integral simulation where both the plasma creation and expansion are incorporated in the same model. This integral approach allows for simulation of expanding plasmas where the Mach number is not known a priori. Results of this integral simulation are validated with semi-analytical models. Inside the creation region the results for the electron temperature, the heavy particle temperature and the electron density are compared with a global model of the creation region. In the expansion region, the simulation results of the compressible flow field are compared with predictions for the shock position. Both the results inside the creation region as well as in the expansion region are in good agreement with the semi-analytical models.

A finite volume model for multi-component diffusion in magnetically confined plasmas

In partially ionized, magnetically confined plasmas, the diffusive fluxes of different species are coupled. Additionally, the fluxes are directionally coupled due to the Lorentz force. The challenge in the modelling of multi-component, magnetized plasmas is to take care of this coupling in the numerical method. In this paper, a complex form of the Stefan–Maxwell equations is used to account for the coupling between the flow directions. To handle the coupling between the species fluxes in the finite volume method, a generalized, coupled form of the exponential scheme is used. The presented numerical method is applied to a magnetically confined hydrogen jet. The results show that the numerical method is capable of describing typical characteristics of magnetized plasmas, such as anisotropic diffusion and the presence of a pressure gradient sustained by the Lorentz force.

Numerical investigation on the replacement of mercury by indium iodide in high-intensity discharge lamps

Mercury-free high-pressure discharge lamps have been studied by means of a radial-dependent model. Xenon and indium iodide are chosen as start gas and buffer, respectively. Local thermodynamic equilibrium is assumed with a single temperature for all species. The model consists of the coupled description of the balance equation for the plasma temperature with the radiation transport equation. The plasma composition is calculated according to the Guldberg–Waage, Boltzmann and Saha laws. These laws were supplemented by additional equations specifying the total pressure, constant element ratios and quasineutrality. The model takes into account atomic, molecular as well as continuum radiation. The broadening of the optically thick lines is approximated by Stormbergs approach. The predicted spectrum is compared with a measured one and shows good agreement on a qualitative scale. From this comparison it is concluded that the largest part of the continuum radiation is produced by the free–free and free–bound AX transition in InI.

A conservative multicomponent diffusion algorithm for ambipolar plasma flows in local thermodynamic equilibrium

The usage of the local thermodynamic equilibrium (LTE) approximation can be a very powerful assumption for simulations of plasmas in or close to equilibrium. In general, the elemental composition in LTE is not constant in space and effects of mixing and demixing have to be taken into account using the Stefan–Maxwell diffusion description. In this paper, we will introduce a method to discretize the resulting coupled set of elemental continuity equations. The coupling between the equations is taken into account by the introduction of the concept of a Peclet matrix. It will be shown analytically and numerically that the mass and charge conservation constraints can be fulfilled exactly. Furthermore, a case study is presented to demonstrate the applicability of the method to a simulation of a mercury-free metal-halide lamp. The source code for the simulations presented in this paper is provided as supplementary material (stacks.iop.org/JPhysD/47/425202/mmedia).

A non-equilibrium simulation of thermal constriction in a cascaded arc hydrogen plasma

The cascaded arc hydrogen plasma of Pilot-PSI is studied in a non-LTE model. We demonstrate that the effect of vibrationally excited molecules on the heavy-particle-assisted dissociation is crucial for obtaining thermal constriction. To the best of our knowledge, thermal constriction has not been obtained before in a non-LTE simulation. Probably, realistic numerical studies of this type of plasma were hindered by numerical problems, preventing the non-LTE simulations to show characteristic physical mechanisms such as thermal constriction. In this paper we show that with the help of appropriate numerical strategies thermal constriction can be obtained in a non-LTE simulation. To this end, a new source term linearization technique is developed, which ensures physical solutions even near chemical equilibrium where the composition is dominated by chemical source terms. Results of the model are compared with experiments on Pilot-PSI and show good agreement with pressure and voltage measurements in the source.

Modeling of diffusive plasmas in local thermodynamic equilibrium with integral constraints: application to mercury-free high pressure discharge lamp mixtures

The mercury free lamp model previously discussed in Gnybida et al (2014 J. Phys. D: Appl. Phys. 47 125201) did not account for self-consistent diffusion and only included two molecular transitions. In this paper we apply, for the first time, a self-consistent diffusion algorithm that features (1) species/mass conservation up to machine accuracy and (2) an arbitrary mix of integral (total mass) and local (cold spot) constraints on the composition. Another advantage of this model is that the total pressure of the gas is calculated self consistently. Therefore, the usage of a predetermined pressure is no longer required. Additionally, the number of association processes has been increased from 2 to 6. The population as a function of interatomic separation determines the spectrum of the emitted continuum radiation. Previously, this population was calculated using the limit of low densities. In this work an expression is used that removes this limitation. The result of these improvements is that the agreement between the simulated and measured spectra has improved considerably.

Harmonic complete flux schemes for conservation laws with discontinuous coefficients

In this paper we discuss several complete flux schemes for advection-diffusion-reaction problems. We consider both scalar equations as well as systems of equations. For the flux approximations in the latter case, we take into account the coupling between the constituent equations. We study conservation laws with discontinuous diffusion matrix/coefficient and show that the (matrix) harmonic average should be employed in the expressions for the numerical fluxes. The vectorial harmonic complete flux schemes are validated for a test problem.

Effects of magnetization on an expanding high-enthalpy plasma jet in argon

The effects of magnetization on an expanding high-enthalpy plasma jet in argon are studied with a non-LTE model. The magnetic field is taken into account with a complete approach where the calculation of diffusion velocities, the electromagnetic field and the flow field are self-consistently coupled via the current density. Results of the simulations show that inside the plasma source there are no significant changes due to the magnetic field. However, in the expansion the magnetic field completely changes the appearance of the jet. Due to the magnetic field, shockwaves disappear and power dissipation not only takes place inside the source but also in the expansion region.