基于湍流模型的DC-RF混合等离子体流动及传热特性研究

Analysis of flow and heat-transfer characteristics of DC-RF hybrid plasma based on turbulence model

直流-射频(Direct Current-Radio Frequency,DC-RF)混合等离子体具有高温、高化学活性等特点,在核用超细粉末材料制备领域有着广阔的应用前景。对这种混合等离子体的特性进行研究,可以为等离子体发生器装置的设计及稳定运行提供参考。本文采用k-ε湍流模型,对DC-RF混合等离子体发生器内的热等离子体的温度及流场空间分布进行模拟,并在此基础上分析了各工作参数对混合等离子体流动及传热特性的影响。模拟结果表明:提高DC弧电流、增大反应气及冷却气流量均能减弱混合等离子体发生器入口处的回流效应;提升RF线圈电流则能增加RF线圈附近的等离子体温度及高温弧区面积,但过大的气流量及过高的线圈电流会对发生器装置的正常工作产生不利影响。因此,需要合理调节各种工作参数来改变混合等离子体的流场分布,从而在保证装置稳定运行的前提下满足不同材料处理的需求。

[Background]Direct-current radiofrequency(DC-RF)hybrid plasma has broad application prospects in the field of nuclear ultrafine powder material preparation owing to its characteristics of high temperature and high chemical activity.[Purpose]This study aims to explore the flow and heat-transfer characteristics of DC-RF hybrid plasma,so as to provide references for the design and stable operation of the plasma generator device.[Methods]First of all,the hybrid plasma generator was assumed to be a two-dimensional axisymmetric model,and the device was filled with pure argon plasma in a local thermodynamic equilibrium(LTE),steady,and turbulent flow state.Then,the ANSYS FLUENT software was employed to establish a two-dimensional model for the DC-RF hybrid plasma torch structure,and the spatial distributions of the temperature and flow field in DC-RF hybrid plasma torch were simulated using the k-εturbulence model with SIMPLE algorithm based on velocity and pressure coupling solver.Finally,the effects of changes in the operating parameters were analyzed based on these results.[Results&Conclusions]The simulation results indicate that increases in the DC arc current,reaction gas flow rate,and cooling gas flow rate can reduce backflow effects at the entrance of hybrid plasma torch.The temperature and area of the plasma arc near the RF coil increase with the RF coil current.However,an excessive current and gas flow rate may adversely affect the operation of the device.Various requirements of material handling processes on the premise of stable operation of the device can be satisfied by adjusting working parameters for the control of the hybrid plasma flow field profiles.