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.

Influence of Metal Material Properties on Heat and Mass Transfer into Thermal Protection Surface with Phenomenological Catalytic Model

Surface heterogeneous catalysis in a high-enthalpy dissociated environment leads to a remarkable enhancement of aerodynamic heating into the thermal protection surface of hypersonic aircraft.To more accurately predict this catalytic heating,a kinetic catalytic model was constructed.This model involved four elementary reactions,the rates of which were determined on mean-field approximation and surface steady-state reaction assumption.By coupling this model into the viscous wall boundary condition of computational fluid dynamics(CFD)solver,the influences of metal material catalytic properties on heat and mass transfer into thermal protection materials were numerically investigated.Numerical results showed that atomic oxygen recombination catalyzed by surface material accounts for a major contribution to aerodynamic heating and thus variation in recombination rates from different materials leads to the significant difference in surface heat fluxes.From a comparative analysis of various materials,the catalytic activity increases from the inert platinum(Pt)to nickel(Ni)and finally to the active copper(Cu).As a result,the catalytic heating on Cu surface was more than twice of that on Pt surface.Further parametrical research revealed that the proper layout of inert material at the nose of aircraft could prevent stagnation catalytic heating from thermal damage by carrying near-wall dissociated atoms from the stagnation zone downstream.The material-relied heterogeneous catalysis mechanism in this study provides some technical support for the thermal protection system design of hypersonic aircraft.