Numerical Study On The Effect Of Particles On Arc Plasma Characteristics

Thermal plasma is widely used in industrial and scientific research fields because of its unique high temperature conditions and active chemical properties.Particle heating is an important issue of arc plasma application,such as spraying high temperature resistant particles,particles spheroidization,and gasification to produce nanomaterials.Compared with plasma jet,the temperature of arc area is higher and is more efficient for particle heating,especially for gasification of high-temperature resistant materials.Through the establishment of the plasma and graphite particle interaction mathematical physics model,this paper studied the particle and arc interaction,arc heating effect of graphite particles,and the influence of interaction on arc characteristics.Firstly,a program for the composition,thermodynamic and transport properties of two-temperature plasma is developed.The plasma composition calculation is based on Eindhoven model.Using the method proposed by Godin can reduce the number of equations,avoid to numerical calculate the Jacobian matrix,and reduce the strict requirements on the initial value of iteration.This method has been used to calculate the components of mixtures of carbon and argon,and carbon and helium under local thermodynamic equilibrium(LTE).Furthermore,the method was extended to non-local thermodynamic equilibrium(NLTE),the composition of argon-nitrogen plasma under NLTE conditions was calculated.The calculation of the thermomechanical properties of the plasma is based on the theory of ideal gas dynamics.The calculation of transport properties is based on a simplified theory of Devoto development,ignoring the collision coupling between heavy particles and electrons.The thermodynamics and transport properties of argon-carbon and helium-carbon plasma under LTE condition were obtained by the above theoretical calculations.The results show that the presence of carbon can increase the electrical conductivity and thermal conductivity of argon plasma and decrease its viscosity.For helium plasma,carbon will reduce the thermal conductivity and viscosity,and greatly improve the electrical conductivity.By applying the above method to NLTE,the thermodynamic and transport properties of argon-nitrogen plasma with the change of electron temperature in NLTE were obtained.Results show that the temperature,pressure and the degree of nonequilibrium affect the chemical reaction processes in the plasma,and thus have a great influence on the thermodynamics and transport properties of the plasma.On this basis,using DPM model,coupled with simplified Maxwell equations,particle moving and heating equations and particle radiation-absorption equations,the interaction between particles and arc plasma was numerically calculated,and the calculated results were compared with the experiment.The results indicate that:(1)The particle density in the high temperature arc is almost zero due to the shielding of the cathode and the thermophore force.(2)The main factors that graphite particles affecting the arc characteristics are the heat absorption of particles and the change of graphite vapor on the thermaldynamic and transport properties of plasma.In the arc column,the plasma temperature is reduced by heat transfer and particle heat absorption,thus the plasma conductivity is reduced.Outside the arc column,due to the heat transfer and particle heat absorption,the arc is compressed and the current density increased.Together,the electric field intensity and arc voltage are significantly increased.(3)With the addition of particles,the arc voltage of helium arc decreases,which is due to the presence of carbon vapor,which improves the electrical conductivity of plasma.When the particle feed rate continues to increase,the arc is compressed due to the heat absorbed by the particles,leading to the arc voltage rise.The direct injection of particles into the plasma torch can reduce the energy loss of the plasma torch,avoid the problems of material cost and increase the thermal efficiency of plasma torch,which will further broaden the application range of arc thermal plasma.