On the space-charge boundary layer inside the nozzle of a cutting torch
- Universidad Tecnologica Nacional, Regional Venado Tuerto, Las Heras 644, Venado Tuerto, Pcia. Santa Fe 2600 (Argentina)
- Departamento de Fisica, Instituto de Fisica del Plasma (CONICET), Facultad de Ciencias Exactas y Naturales, UBA, Ciudad Universitaria Pab. I, Buenos Aires 1428 (Argentina)
A numerical study of the space-charge sheath adjacent to the nozzle wall of a cutting torch is presented. The hydrodynamic model corresponds to a collision-dominated sheath and does not assume cold ions, so drift-diffusion-type equations are used. Also an improved expression for the ion-neutral momentum transfer is employed rather than the usual constant ion-mean-free-path or constant ion collision frequency approximations. Assuming a constant electron temperature in the sheath and neglecting the electron inertial term, the continuity and momentum equations for ions and electrons, together with Poisson's equation, were solved for the electric potential, ion velocities (both normal and tangential components), and for the ion and electron densities. It was found that both the ion and electron densities present a sudden drop at the sheath-plasma edge. The ion density continues to decrease slowly inside the sheath, while the electron density presents a virtually zero value everywhere inside the sheath, the electron thermal conduction flux to the nozzle wall being negligible. These wall results thus become thermally isolated in spite of the high electron temperature in its adjacency. For a nozzle biasing voltage close to the gas breakdown, it was found that the electric field value is high, reaching a value of about 9x10{sup 6} V m{sup -1} at the exit of the nozzle wall. This value is higher than the average field value across the sheath and is on the order of the breakdown threshold value. This means that an undesired sheath breakdown could occur at the vicinities of the nozzle exit even if the average electric field across the sheath is not strong enough.
- OSTI ID:
- 21352246
- Journal Information:
- Journal of Applied Physics, Vol. 105, Issue 12; Other Information: DOI: 10.1063/1.3153147; (c) 2009 American Institute of Physics; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
APPROXIMATIONS
BOUNDARY LAYERS
BREAKDOWN
ELECTRIC FIELDS
ELECTRIC POTENTIAL
ELECTRON DENSITY
ELECTRON TEMPERATURE
HYDRODYNAMIC MODEL
ION COLLISIONS
ION DENSITY
ION TEMPERATURE
MEAN FREE PATH
MOMENTUM TRANSFER
NUMERICAL ANALYSIS
PLASMA
PLASMA DENSITY
PLASMA SHEATH
POISSON EQUATION
SPACE CHARGE
THERMAL CONDUCTION
CALCULATION METHODS
COLLISIONS
DIFFERENTIAL EQUATIONS
ENERGY TRANSFER
EQUATIONS
HEAT TRANSFER
LAYERS
MATHEMATICAL MODELS
MATHEMATICS
PARTIAL DIFFERENTIAL EQUATIONS
PARTICLE MODELS
STATISTICAL MODELS
THERMODYNAMIC MODEL