Comparative analysis of the arc characteristics inside the convergingdiverging and cylindrical plasma torches

A two-temperature thermal non-equilibrium model is used to simulate and compare the arc characteristics within the converging-diverging and traditional cylindrical plasma torches.The modeling results show that the presence of the constrictor within the converging-diverging torch makes the evolution characteristics of the arc significantly different from that of cylindrical torch.Compared with a cylindrical geometrical torch,a much higher plasma flow velocity and relatively longer high temperature region can be generated and maintained inside the converging-diverging torch.In the constrictor of converging-diverging torch,the normalized radius of arc column increases and the degree of thermodynamic equilibrium of the plasma is significantly improved with the increase of axial distance.The radial momentum balance analysis shows that for the cylindrical torch,the pressure gradient that drives the arc expansion and the Lorentz force that drives the arc contraction dominate the radial evolution of the arc.While at the converging and constrictor region of a converging-diverging plasma torch,the radial gas dynamic forces in arc fringes pointing toward the arc center enhance the mixing of the cold gas of boundary layer with the high temperature gas of the arc center,increasing the average gas temperature and decreasing the thickness of cold boundary layer,thereby facilitating the formation of diffusion type arc anode attachment at the diverging section of torch.

Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model

A detailed understanding of anode heat transfer is important for the optimization of arc processing technology.In this paper,a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc.The temperature,total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials.It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column.As the arc current increases from 100 A to 200 A,the total anode heat flux increases,however,the maximum electron condensation heat flux decreases due to the arc expansion.The anode materials have a significant effect on the temperature and heat flux distributions in the anode region.The total heat flux on thoriated tungsten anode is lower than that on copper anode,while the maximum temperature is higher.The power transferred to thoriated tungsten anode,ranked in descending order,is heat flux from heavy-species,electron condensation heat,heat flux from electrons and ion recombination heat.However,the electron condensation heat makes the largest contribution for power transferred to copper anode.