Numerical analysis of direct-current (DC) plasma processing for high-efficient steel surface modification

Abstract

Nowadays, direct-current (dc) non-transferred arc plasma torch has drawn significant interest from both academia and industry due to the capability to process products in an efficient and convenient way. The core of this technology is to clarify and manipulate the arc behavior at the interior of the dc plasma torch to produce ideal plasma jets for processing. To solve this problem, a quasi-steady axisymmetric model is built to simulate and compare the arc characteristics in different operating conditions and different nozzle structures of the plasma torch. The results uncover distinct aspects of the study on arc characteristics, including the detection of the primary arc attachment region and its spatial features caused by the choking effect of torch structure. The thermal efficiency focused on processing substrate is also calculated in this paper for estimating the performance of plasma processing. The calculated results show that increasing the mass flow rate brings better thermal efficiency and the greatest promotion is at least 6% in the same current value, whereas improving the arc current value causes the opposite result. Meanwhile, two types of nozzle are compared to the original design in thermal efficiency, where the wide nozzle is chosen for torch optimization due to its best power efficiency. The secondary arc attachment on the metal substrate is discovered though its impact scope is only within a radius of 10 mm from the torch axis, its effect on the processing could be ignored for the extremely low electric current value.

A Review of Simulation Modeling of the State Evaluation and Process Prediction of Plasma Processing under Atmospheric Pressure

“…Plasma can be generated by imparting energy to neutral gas, leading to the reorganization of its electronic structure [8]. Various methods utilizing different energy supplies, such as thermal [8], electric current [9][10][11][12][13][14], or electromagnetic radiation [1,[15][16][17][18][19], have been employed to achieve plasma generation. Technically, under the influence of external input energy, when the energy of molecular thermal kinetic motion reaches that required for gas ionization, abundant ionization events occur through collisions with neutral gas particles.…”

“…(2.2) Re = uL Recent studies [111] have highlighted that the region near the electrode in arc plasma is not fully in the LTE state because of the relatively low electrical conductivity caused by some factors, such as the cooling effect from the electrode cooling system and complex physical processes, such as the plasma sheath adjacent to the electrode surface. To enhance the accuracy of arc plasma generation simulation modeling within the LTE assumption, researchers tend to define a local thin layer (sheath layer) near the electrode with constant electrical conductivity as a complement [14]. This modification not only retains the advantages of lower computational cost with the LTE assumption but also improves the prediction precision of the arc root near the anode.…”