A Study On The Influence Of Alkali Metal Implantation On The Multiphysics Of Plasma

Plasma has many important applications in scientific research and industrial production.In the flow generated by the magnetic fluid power generation and the plasma sheath ground simulation device,the temperature is usually only about 3000 K,so alkali metals are often injected into the working medium,and the thermal ionization of the alkali metals is used to improve the electron number density and electrical conductivity of the gas.A large number of alkali metals have been used as ionization seeds in both domestic and foreign magnetic fluid power generation.Considering the environment difference between the plasma sheath ground simulation device and MHD with also its multi-physics coupling,studies on the effects of alkali metal injection parameters on the physical fields such as temperature,velocity and electron number density of the working medium are very necessary.Aiming at this problem,this article starts with the physical and chemical process of alkali metal injection and abstracts model of the problem.Based on a self-designed simulation model,CFD software is used to perform 3D numerical simulation to predict the distribution of temperature and component concentration under different operating parameters;it also explores the influencing factors of injection form,powder size and flow,boundary temperature and injection speed.The main content of this article is described as below:(1)This article introduces the motion law of the two jets intersection,which are the carrier gas of the alkali metal and the working medium;it also describes the interaction law between the alkali metal and the high-temperature gas,that is,the process of momentum,heat and mass transfer between the discrete phase and the continuous phase;and it finds out the governing equation of each component and the calculation method of the reaction rate between the components.(2)According to the law of jet motion,different injection models of alkali metal powder are compared in this paper: vertical incidence,oblique incidence,tangential incidence,and rotating intake air.During the numerical calculation,the k-e model is selected as the turbulence model,according to the particle loading the Discrete Phase Model is used to describe the interaction between the discrete phase and the continuous phase.At the same time,the vaporization process and the ionization reaction after the injection of alkali metals are also calculated using the chemical reaction model,and this article sets all the boundary conditions according to the actual situation in the project.(3)The simulation of alkali metal powder injection process under different groups of parameters was performed,and the influence of each variable on the thermal parameters(temperature,velocity,pressure,etc.)and concentration distribution is analyzed.Comparing the field distribution results under different injection models,it is found that selecting the oblique incidence structure while the main pipe adopting the rotary inlet may result in higher outlet electron number density and better distribution consistency in practical application.By comparing the calculation results of different alkali metal particle sizes and injection amounts,it is found that smaller particle size will make outlet electron number density and the degree of uniformity higher,so the particle size should be minimized as far as the cost is acceptable;there is an optimal value for the injection volume of alkali metal.For the case where metal elemental potassium is used as the ionization seed,the recommended injection volume is 2.5% of the main gas flow rate.After simulation we found that outlet electron number density increases with the increase of the main gas flow temperature and the carrier gas temperature.Finally,the idea of controlling the mixing intensity by changing the carrier gas flow rate(jet velocity)is also proposed.The boundary conditions of implementing different penetration depth are given.The research content of this article is an important part of the plasma sheath ground simulation device.With the continuous deepening of the research on how alkali metals improves the electron number density,on one hand,the different alkali metal injection forms proposed in this subject have great application value;on the other hand,the simulation on the effects of parameters such as particle size,injection volume,boundary temperature,and carrier gas flow rate of the alkali metal in this paper provides reliable reference for subsequent research on optimizing non-equilibrium plasma generation.