Modelling of arc behaviour inside a F4 APS torch

Abstract

The plasma arc inside the F4 torch used for atmospheric plasma spraying is characterized by means of analytical and numerical methods. A simplified analytical model is formulated to understand the physical behaviour of the plasma arc. A three-dimensional numerical model is developed to simulate the realistic plasma arc flow inside the torch. At a given torch power and gas flow rate, possible combinations of the arc core radius and arc length are predicted. The thermodynamic principle of minimum entropy production is used to determine the combination of arc core radius and arc length, which corresponds to the actual physical situation of the arc inside the torch. The effect of arc current and gas flow rate on the plasma arc characteristics is clarified. The effect of hydrogen content in the plasma gas on its velocity and temperature profiles at the nozzle exit is shown. Predicted torch efficiencies are comparable to measured ones. The results of the numerical model are similar to that an analytical model. Previously published experimental and numerical results support part of the present results.

Effect of the deviation of the current density profile center on the three-dimensional non-transferred arc plasma torch

“…2 and Tab. 1, respectively [13]. The computational domain is meshed into 319,756 hexahedral cells with the refined mesh at the near-wall region.…”

“…Both two-dimensional [1][2][3][4][5][6][7] and three-dimensional [8][9][10][11][12][13][14][15][16][17] models have been adopted to study the plasma spray inside the torch. In some cases for steady-state simulation, zero electrical potential was imposed to the anode spot and zero gradient electrical potential was imposed to the rest region of anode, which can lead to the current passing through the anode [8,13].…”

“…In some cases for steady-state simulation, zero electrical potential was imposed to the anode spot and zero gradient electrical potential was imposed to the rest region of anode, which can lead to the current passing through the anode [8,13]. Although steady-state simulation can provide sufficient information of the plasma flow field, it is not applied to all circumstances because the real arc always moves on the anode wall and operates in different modes depending on the working conditions.…”

“…In previous works, one can notice that the maximum current density are always located at the center of the cathode tip [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], particularly for transient models concerning the time-dependent plasma [21][22][23]. Actually, the maximum value of the current density profile imposed on the cathode surface may not be located on the center of the cathode.…”

“…Therefore, it is meaningful to well understand the effect of ADCD (here, asymmetrical distribution of current density means the maximum value of current density is not at axis of the cathode tip) on the plasma flow fields. In this study, the F4 APS torch (a common torch for thermal spray) with 3mm nozzle size that is also stated in [13] is adopted.…”