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P: Plasmaphysik

P 10: Niedertemperaturplasmen / Plasmatechnologie 3

P 10.4: Talk

Tuesday, March 28, 2006, 12:15–12:30, 1002

Modelling of a water plasma flow: various effects — •Pavel Kotalik and Detlef Loffhagen — INP Greifswald, F.-L.-Jahn-Str. 19, 17489 Greifswald

Plasma spraying with the so-called water stabilized plasma torch led to attempts to increase the velocity of the water plasma by suitable nozzle shapes and lengths of the water-vortex stabilized part of the electric arc. Results of the numerical solution of one-fluid MHD equations for the axisymmetric, atmospheric pressure plasma flow inside and outside the discharge chamber of the torch are presented for two conical nozzles made of copper. It is shown that these nozzles do not increase substantially the gas velocity and that comparable or better results can be obtained with converging-diverging nozzles of smaller diameter. A variation of the length of the vortex surrounding the arc between 5.5 and 6 cm has little effect on the exit velocity and temperature as well. Narrower copper-made nozzles need an efficient cooling, however. For the heat fluxes estimated by means of the fluid model, the heat transfer equation is solved inside copper and its surrounding materials for different designs of the nozzles in order to estimate the temperature of nylon parts of the surrounding material that might be damaged if not cooled properly. High risk of melting of the downstream nozzle edges is predicted and confirmed experimentally. Based on the numerical predictions, some of the newly designed nozzles had to be modified or excluded from use at all.