Hydrodynamic model for the plasma-gas flow in a cutting torch nozzle

Abstract

We present a simple hydrodynamic model to obtain the profiles of the relevant physical quantities along a nozzle of arbitrary cross-section in a cutting torch. The model uses a two-zone approximation (a hot central plasma carrying the discharge current wrapped by a relatively cold gas which thermally isolates the nozzle wall from the plasma). Seeking for a solution with sonic conditions at the nozzle exit, the model allows expressing all the profiles in terms of the externally controlled parameters of the torch (geometry of the torch, discharge current, mass flow of the gas and plenum pressure) and the values of the arc and gas temperatures at the nozzle entrance. These last two values can be estimated simply appealing to energy conservation in the cathode-nozzle region. The model contains additional features compared with previous reported models, while retaining simplicity. The detailed consideration of an arc region coupled to the surrounding gas dynamics allows determining voltage drops and consequent delivered power with less assumptions than those found in other published works, and at the same time reduces the set of parameters needed to determine the solution.

Experimental characterization of a low-current cutting torch

“…The obtained experimental quantities are used to evaluate several flow properties at the nozzle exit (hot arc plasma and cold gas temperatures, arc and gas velocities, etc.) by employing a simplifi ed theoretical model for the * Member of the CONICET plasma flow in the nozzle [7]. The obtained results are in reasonable agreement with the data reported in the literature by other authors [2,3,4,5,6].…”

“…In order to interpret the experimental results presented in the previous section, some of them were compared with theoretical results obtained from a simplifi ed hydrodynamic model for the arc in the torch nozzle [7]. That model uses a two-zone approximation (a hot central plasma carrying the discharge current surrounded by a relatively cold gas that thermally isolates the nozzle wall from the plasma) and allows to obtain the profi les of the physical quantities along the nozzle in terms of the externally controlled parameters of the torch (geometry of the torch, discharge current, mass flow of gas and plenum pressure) and the values of the arc and gas temperatures at the nozzle entrance.…”

Numerical Modelling of a Cutting Arc Torch

“…All this is more clearly seen and quantified using simple 1-D, two zone models in which only axial dependence is considered of an inner hot zone and an outer cold region. By assuming sonic flow at the nozzle exit, these simple 1-D models are able to predict quite reasonably the measured temperatures (within the experimental uncertainty), but give very imprecise values (100% off) of the flow velocity (Kelly et al, 2004).…”

Interpretation of Voltage Measurements in Cutting Torches

“…Finally, the difference of potential between anode and cathode is evaluated assuming constant electrical field out E in the arc outside the nozzle (equal to its value at the nozzle exit), so that The model is based on a previously presented one [4], which was extended to allow for mass exchange between arc and gas. Besides, the new model does not require the imposition of sonic conditions at the nozzle exit (used in the previous model), and was also improved in the modeling of radiated power.…”

“…The equations of mass conservation, axial momentum and energy for the arc and gas regions, valid inside the nozzle, are (the notation is that used in [4])…”