电感耦合等离子体离子源气体温度特性数值模拟分析.

Computational Fluid Dynamics (CFD) method coupled electromagnetic field is used to analyze thermal characters of inductively coupled plasma （ICP） with and without sampler. The ICP is modeled in an axisymmetric geometry, taking into account the gas streaming into a flowing ambient gas. The flow in the calculation region is assumed to be laminar and the well-known Navier-Stokes equations are used to determine the flow conditions. The time-averaged Axial and Radial Lorentz Force density is taken as Axial and Radial Momentum source respectively. Since the energy loss by emitted radiation is much lower than the coupled electric power density, it is negligible in this numerical simulation. The advantage of choosing CFD commercial software Ansys Fluent is that user-defined scalar (UDS) method can be applied to solve Maxwell's equations. On the other hand, user-defined function is a convenient way to add Ar-ICP's physical characters, which can be described by mathematic functions, like viscosity and thermal conductivity. Under the hypothesis of Local Thermal Equilibrium (LTE), electron density and electron temperature can be calculated based on gas temperature. The temperature of Nickel sampler interface cooled by water was set as 1700 K which is below the melting point of pure Nickel. The flaw of this numerical simulation method was the distribution of electrical conductivity σ(T) which is related to gas temperature. Because several equations need to be solved in the process of iterations, there is no other way to do it if σ(T) is unpredictable. In this case, the crucial parameter will be missing. But it is contradictory that if σ(T) is predictable then gas temperature can be predictable too. Although many references set σ(T) as a constant number at the beginning of iterations, a simple mathematical function will help to do better but not perfectly. Besides, the process of how tested element diffuses in ICP is hardly estimated by this model. Gas temperature is a little higher with sampler orifice because it becomes a relatively closed space between ICP torch and sampler. But the nearest area of sampler position has cooler temperature and the effect of plasma central tunnel is stronger. Gas temperature of central tunnel rises fast to about 8 000 K from axial position around 25 mm and drops down quickly to about 6 000 K from axial position around 1 mm in front of sampler position. To study how aerosols with different diameters affect the gas temperature of central tunnel, Discrete Phase Model (DPM) was used. Aerosols with diameters of several microns have higher probability to be ionized. [ABSTRACT FROM AUTHOR]