Three-dimensional, unsteady behaviour of high-pressure electric arcs in argon is studied by means of numerical simulations. Attention is paid to argon arcs whose steady structure is fairly well understood. Results are reported for the case of a one centimetre long arc, burning in argon and driven by a total current of 200 A and 300 A. The influence of the boundary conditions for the electrical potential on the macroscopic structure of the arc is studied and it is found that the distribution of the current density near the cathode is one of the critical parameters which can significantly modify both the distribution of mean quantities and the stability of the arc. All mean quantities found from three-dimensional calculations are compared with two-dimensional axi-symmetric fields obtained by a previously used code for arc simulations. The results indicate good agreement between the results from three-dimensional calculations, two-dimensional axi-symmetric simulations and results from physical experiments documented in the literature.

The net flux of vapour from a solid surface in an ambient gas is analysed with the aim to estimate the effect of vaporization cooling on the energy balance of an arc cathode under conditions typical for a high-power current breaker. If the ratio of the equilibrium vapour pressure p v to the ambient pressure p ∞ is smaller than unity, the removal of vapour from the surface is due to diffusion into the bulk of the gas. As a consequence, the net flux of the vapour from the surface is much smaller than the emitted flux. An estimate of the diffusion rate under conditions typical for a high-power current breaker indicates that vaporization cooling plays a minor role in the energy balance of the cathode in this case. If ratio p v /p ∞ is above unity, the flow of the vapour from the surface appears and the net flux is comparable to the emitted flux. A simple analytical solution has been obtained for this case, which is in a good agreement with results of the Monte Carlo modelling of preceding authors. If p v /p ∞ exceeds approximately 4.5, vaporization occurs as into vacuum and the net flux is about 0.82 of the emitted flux.

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When a liquid droplet experiences a temperature inhomogeneity along its bounding surface, a surface energy gradient is engendered, which when, in a continuous sense, exceeding a threshold, results in a convective flow dissipating the energy. If the associated temperature gradients are sustained by the interface between the liquid and a supporting substrate, the induced flow can result in the lateral motion of the droplet overcoming the viscosity and inertia. Recently, pico-liter adsorbed and applied droplets were shown experimentally to be transported, and divided by the decay of optically excited surface plasmons into phonons in a thin gold foil. The decaying events locally modify the temperature of the liquid-solid interface, establishing microscale thermal gradients of sufficient magnitude for the droplet to undergo thermocapillary flow. We present experimental evidence of such gradients resulting in local surface modification associated with the excitation of surface plasmons. We show theoretically that the observed effect is due to Marangoni forces, and computationally visualize the flow characteristics for the experimental parameters. As an application based on our results, we propose a method for an all-optical modulation of light by light mediated by the droplet oscillations. Furthermore, the results have important consequences for microfluidics, droplet actuation, and simultaneous surface plasmon resonance sensing and spectroscopy.

A complete set of equations is proposed to model droplets of molten metal ejected from the contacts in a high voltage circuit breaker of the SF6 filled gas-blast type. The initial speed and diameter of the droplets are varied to characterize their behaviour and study the distribution of the metal vapour. A relation is derived that can be used in simplified arc models such as integral or two-zone models to take the effect of the droplets into account. It is found that, although the influence on usually measured quantities such as pressure and voltage is small, droplets affect velocity and temperature fields in the electric arc significantly and should not be neglected.