Numerical Research On Direct Current Micro-Plasma Arc Output Characteristics At Atmosphere

Micro-plasma arc(MPA)has been widely used for its large energy density,high energy efficiency,low cost equipment and low requirement of production environment.Its high temperature and temperature gradient lead to a lack of reliable,effective experimental equipment for direct measurement.However,the distributions of its temperature field and other physical fields have very important influence to guide the use of MPA.With the development of computer technology,the use of numerical simulation has become an important method to study the characteristics of MPA.The numerical simulation of the MPA involves the multi-physics coupling of the flow field,the temperature field and the electromagnetic field.At the same time,there is a complex heat and mass transfer process between the transmitting cathode,the plasma arc and the anode.As the program calculation is extremely difficult based on the existing computer software.Therefore,the COMSOL 5.2 Multiphysics software is used in this study,along with coupling to solve the electromagnetic field and fluid mechanics equation,established a two-dimensional axisymmetric transient numerical model of the MPA with pulsed direct current.The calculation includes the cathode,the nozzle,the anode workpiece and the MPA.The simulation results of the multi-physics numerical model are close to the experimental results.The main results are as follows:(1)The time domain characteristics and the spatial distributions of the physical fields of the pulsed direct current MPA are simulated.As the input current changes,the potential,the current density,and the total heat source exhibit with pulsating properties.The mechanical compression,hot compression and self-magnetic compression of the nozzle are important conditions for obtaining a stable MPA.Due to the compression of the nozzle,the total heat source and current density distribution within the nozzle is much smaller than the free diffusion region of the MPA.It is also found that the Joule heat is the main heat source component of the MPA.The enthalpy of electrons can be transferred on the surface of the cathode and anode,and the effect of enthalpy is obvious.(2)The breakdown effect of the plasma is simulated on the rising edge of the input current.After the potential between the cathode and anode reaches the peak,the ionization of the gas between the cathode and anode form the plasma at room temperature.When the movement velocity of plasma to reach the maximum,the current density and the total heat source also reach the maximum,these promotes the increasing of the temperature of the plasma.Whilst the input current reaches its maximum value,the potential,the current density and the total energy are output in a more stable way,the temperature and the velocity of the plasma reach the seasonal stable state.(3)The influence of the main parameters such as the nozzle diameter,the distance from the nozzle to workpiece,the arc current,ionized gas flow rate and the cathode height on the MPA are simulated.(4)Compared with the results of the numerical simulation and the experimental on the electron temperature,electron density of the arc column area from MPA,and the workpiece surface temperature distribution,it shows that the numerical simulation results are in good agreement with the experimental results,this verifies the reliability of the numerical model proposed in this paper.