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Generation of Long Laminar Plasma Jets: Experimental and Numerical Analyses

  • Sen-Hui Liu
  • Shan-Lin Zhang
  • Cheng-Xin LiEmail author
  • Lu Li
  • Jia-Hua Huang
  • Juan Pablo Trelles
  • Anthony B. Murphy
  • Chang-Jiu Li
Original Paper
  • 59 Downloads

Abstract

A novel direct current non-transferred arc plasma torch that can generate silent, stable and super-long laminar plasma jets in atmospheric air is investigated. The results showed that laminar plasma jets of length ranging from 100 to 720 mm in length can be generated by controlling the gas input rate ranging from 8.5 to 15 L min−1 and the output power from 8.5 to 28 kW. The length of the plasma jets generally increased with the output power and gas flow rate. Observations of temporal evolution of the plasma jet appearance and the voltage demonstrated that the jet is highly stable in the atmospheric environment. The fluid dynamic properties of the laminar plasma jet were studied using a numerical simulation incorporating a laminar flow model and an RNG turbulent flow model. Simulation results show the expansion of a high temperature region close to the torch nozzle exit, corresponding to a bright region observed in experiments.

Keywords

Laminar plasma jet Voltage current characteristics Voltage vibration Numerical simulation 

List of Symbols

Cp

Specific heat at constant pressure (J kg−1K−1)

E

Electric field (V m−1)

T

Temperature (K)

W

Power (W)

I

Current (A)

Q

Gas flow rate (kg s−1)

k

Turbulent kinetic energy (m2 s−2)

Greek Symbols

ε

Dissipation rate of turbulent kinetic energy (m2 s−3)

εr

Net emission coefficient (W m−3sr−1)

κ

Thermal conductivity (W m−1K−1)

μ

Dynamic viscosity (kg m−1s−1)

μt

Turbulent viscosity (kg m−1s−1)

μeff

Effective viscosity (kg m−1s−1)

σ

Electrical conductivity (S m−1)

ρ

Density (kg m−3)

ϕ

Electric potential (V)

Abbreviations

LTE

Local thermodynamic equilibrium

RNG

Renormalization group methods

MHD

Magnetohydrodynamic model

NEC

Net emission coefficient

Introduction

Thermal plasmas are characterized by heavy-particle and electron temperatures of order 104 K, and typically operate at or near atmospheric pressure. They can be generated by electric arcs, which have high current densities, and can be transferred to the workpiece (as, for example, in arc welding, plasma cutting and other applications) or non- transferred (as, for example, in plasma spraying) [1]. In the non-transferred arc plasma torch, high temperature is achieved through a direct current (dc) arc induced between a conical cathode and an anode nozzle [2]. The arc properties depend on the internal-channel design of the torch, the type of working gas and its flow rate, the arc current and other operating parameters. The arc generates the high-temperature plasma through continuous energy dissipation of the current flowing through the gas. The plasma jet exits the torch from the anode nozzle, subsequently experiencing deceleration and cooling due to its interaction with the cold gas from the discharge environment. As a representative example, at an axial position of 100 mm from the nozzle exit, a pure argon plasma jet consists of about 80% air in an atmospheric environment [3]. The length of plasma jet in an atmospheric environment is usually less than 200 mm. Non-transferred arc plasma jets are used in deposition, gasification, waste conversion, metallurgy, some welding and cutting processes, and plasma spraying.

Arc plasma torches generally operate at high output power (25–150 kW) and high gas flow rate (usually ≥ 30 slpm) [2, 3], and generate high levels of noise to the surrounding environment (≥ 120 dB). In the atmospheric plasma spraying process, the fluid dynamics of the plasma jet lead to the development of turbulence associated with strong entrainment of ambient gas into the plasma jet, lowering the controllability and reproducibility during the plasma spraying process [4, 5]. The fluctuation behavior of the plasma jet and the internal arc instabilities also significantly affect both torch performance and coating quality [6, 7].

An alternative type of plasma jet is the laminar plasma jet, which operates at a relatively low Reynolds number at the nozzle exit and reduces turbulent cold gas entrainment and the axial attenuation of the jet temperature and velocity. During the past three decades, several groups around the world have researched direct-current non-transferred arc plasma torches that can generate stable, long, quasi-laminar or totally laminar plasma jets. Zhukov and coworkers took the lead in designing a powerful high-enthalpy direct current plasma torch that was applied to plasma chemical technologies [1, 8]. Their design featured several linear interelectrode inserts between the cathode and the anode to extend the arc column [9].

Subsequently, a plasma torch with a much larger nozzle outlet and a jet length up to 600 mm was developed by Hamatanis of the Nippon Steel Corporation in 1999. This torch used an optimized interelectrode geometry and was used in metallic pipe butt welding and the synthesis of fine powders [10, 11].

At almost the same time, W. X. Pan and C. K. Wu from the Chinese Academy of Science designed an argon- nitrogen direct- current plasma torch that can generate a long, silent and stable plasma plume within a wide range of working parameters in either the ambient environment or in a low-pressure environment [12, 14]. The laminar plasma jet had a length up to 45 times its diameter and was applied to depositing thermal sprayed coatings and for strengthening metallic surfaces by remelting [12, 13]. Since then, researchers from Pan’s group and Chen Xi’s group studied the flow characteristics of this laminar plasma torch and jet using experimental and numerical simulation methods. These works included the studies of torch geometry and the voltage–current characteristics [14, 15, 16], experimental measurement of the jet flow field [17, 18] and the heat flux density of the plasma plume [19]. They performed experimental and numerical investigations of the laminar plasma jet impinging on a substrate [20, 21, 22, 23, 24], observations of the arc root motion in the cylindrical channel of the plasma torch [25] and two and three-dimensional modelling of laminar plasma jets with or without the entrainment of ambient air and a cylindrical shield [26, 27, 28, 29]. These results explored the effects of natural convection and lateral particle injection on the laminar plasma jet [30, 31] and compared the performances of turbulent and laminar plasma jet using experimental and numerical analyses [28, 32]. These fundamental studies and practical achievements made huge contributions to the field of laminar plasma torch research.

In the thermal spraying research area, the huge entrainment of surrounding gas and turbulent transport in the plasma plume always occurred in atmospheric environment. The coating quality is significantly affected from the jet instabilities of the plasma torch [33]. This newly developed laminar plasma torch has significant potential for application in advanced thermal spraying processes [12, 34, 35] and other materials processing technologies [9, 11, 13].

In this work, a novel direct-current non-transferred arc plasma torch with a unique inside channel structure is presented. This torch can also generate long, silent and stable laminar plasma plumes in atmospheric environment at different gas flow rates and output powers. The fluid dynamic properties of the laminar plasma jet have been studied by a combination of experiments and numerical simulation. Experiments have been conducted to study the voltage–current and plasma jet flow characteristics under various working parameters, including the jet lengths variation, time-resolved of arc voltage fluctuation and jet plume. The numerical simulation was modelled in two-dimensional calculation domain by using Laminar model and RNG turbulent transport model.

Characteristics of Plasma Jet, Power Supply and Working Parameters

Properties of the Laminar Plasma Jets

Figure 1 shows a schematic diagram of the direct-current non-transferred laminar plasma torch (ZH-30, Zhenhuo Plasma Technology Co. Ltd., Chengdu, China) used in this study. It is composed of a cathode, insulated inserts, an anode and a nozzle outlet. The diameter of the nozzle exit is 5 mm, and the insulated inserts are assembled with several insulating rings to extend and constrict the arc column in a cylindrical channel. The length of the insulated inserts can be changed depending on the desired applications. The trumpet-like structure of the anode is, however, innovative, and leads to the specific characteristics of the plasma flow near the torch exit that are beneficial for the generation of a stable laminar plasma jet. The details of the design and the fluid dynamic characteristics inside the plasma torch are presented elsewhere [36]. The rated output power is 30 kW. The working gas is a mixture of 70% nitrogen and 30% argon by volume, unless otherwise noted. In fact, both pure argon and pure nitrogen can generate long laminar plasma jet in ambient air, although the plasma plume with this mixture is more stable and leads a longer service life in experiment.
Fig. 1

Schematic diagram of internal structure of the laminar plasma torch

The in situ experimental measurement of jet length in atmospheric environment are shown in Figs. 2, 3 and 4 by using the Nikon D3400 camera, regular laminar plasma jets can be generated from the laminar plasma torch under a wide range of output power and gas flow rates, producing a low-level of noise (< 80 dB) in the ambient environment. When the inlet gas rate was lower than 8.5 L min−1 or higher than 15 L min−1, the plasma jets become uniformly short (about 80 mm) and extremely noisy (about 110 dB) because of intense entrainment of ambient air, just as in the case of conventional direct-current non-transferred arc plasma jets.
Fig. 2

Laminar plasma jet, showing variation in length for different working current. a Gas flow rate of 8.5 L min−1; b gas flow rate of 11.5 L min−1

Fig. 3

Laminar plasma jet, showing variation in length for different working current. a Gas flow rate of 14 L min−1; b gas flow rate of 15 L min−1

Fig. 4

Laminar plasma jet, showing variation in length for different gas flow rates. a I = 100 A; b I = 160 A

A wide range of laminar plasma jet lengths can be obtained by increasing the current from 60 to 165 A under the corresponding gas flow rate from 8.5 to 15 L min−1 (Fig. 5). The maximum length of the laminar plasma jet reaches 720 mm at a current of 160 A and a gas flow rate of 8.5 L min−1; this is longer than the values obtained in other published studies [9, 11, 14]. At the high gas flow rate of 15 L min−1 and a current of 160 A, a stable laminar plasma jet with a length greater than 200 mm is also generated (Fig. 3b). As shown in Fig. 4, the length of the laminar plasma jet decreased approximately monotonically with increasing gas flow rate at a given current. The laminar plasma jets at a current of 160 A (Fig. 4b) were all longer than those at a working current of 100 A (Fig. 4a) for every gas flow rate investigated, suggesting that the higher output power associated with the higher current increases the nozzle exit temperature and velocity.
Fig. 5

Dependence of laminar plasma jet length on arc current for different gas flow rates

A bright emission region appears in the vicinity of the nozzle orifice at higher gas flow rates and output power. The time-resolved voltage fluctuations during the laminar plasma torch operation are shown in Fig. 6. (The voltage was measured using a TPS-2000 probe manufactured by Tektronix Inc. USA). The voltage fluctuation values were confined within a range of between ± 0.5 and ± 2 V, depending on the operating conditions, which was significantly lower than those found in other commercial non-transferred arc plasma torches under higher voltage fluctuation conditions (voltage fluctuations are usually in the range of ± 5 V up to about ± 20 V) [5, 37]. Relatively low voltage fluctuations were also observed with the laminar plasma torch of W. X. Pan et al. [14].
Fig. 6

Time-resolved arc voltage at the working current of 160 A and gas flow rate of 14 L min−1

The time-dependent stability of the arc plasma jet were monitored using a high-speed micro-lens camera (Nikon AF MICRO 200 mm) at the nozzle exit. The jet was found to be quite stable, as shown in Fig. 7 and the supplementary video file. The stability in an atmospheric environment will be useful for application to plasma processes such as deposition, welding, surface hardening and to provide a substantially improved working environment.
Fig. 7

Photo showing the nozzle exit part of a long laminar plasma jet obtained with a high-speed micro-lens camera with exposure time of 1/200 s (I = 160 A, gas flow rate = 14 L min−1)

Arc Voltage–Current Characteristics Under Various Conditions

Arc Voltage Current Characteristics in Different Gas Mixtures

The chosen working gas was a nitrogen and argon mixture, with pure argon used to start the arc, and pure nitrogen as the secondary gas to obtain a longer laminar plasma jet. Argon is a monatomic inert gas with low thermal conductivity and energy density. Its use is beneficial for the service time of the electrode and nozzle as its use limits the heat transfer to the edge regions. Nitrogen has much higher thermal conductivity and power density than pure argon. Since it is a molecular gas with a strong bond energy, it absorbs a large amount of energy during the dissociation process, and the release of this energy by recombination reactions enhances the heat transfer between the cold gas and the arc column. The arc voltage of pure nitrogen is about twice that of the pure argon at the same gas flow rate. Figure 8 shows a comparison of the arc voltage and plasma jet length for two mixtures of nitrogen and argon, with 80% (Fig. 8a) and 70% (Fig. 8b) nitrogen by volume. The working voltages for the 80% nitrogen working gas were found to be higher for all currents.
Fig. 8

Variation of laminar plasma jet length and arc voltage for a gas flow rate of 8.5 L min−1, a for N2:Ar = 8:2 by volume; b for N2:Ar = 7:3 by volume

Arc Voltage–Current Characteristics for Different Gas Flow Rates

The measured voltage–current characteristics for different gas flow rates are shown in Fig. 9. The arc voltage generally increases with both the gas flow rate and arc current. The minimum voltage of the laminar plasma torch was larger than 135 V. However, with an increase in arc current from 60 to 165 A, the increase in voltage was just 10 ± 2 V for all gas flow rates. As was shown in Fig. 6, the voltage fluctuation values were confined to the range of ± 0.5–2 V. Both the rate of change of voltage with current and the voltage fluctuations are much lower than those of conventional current non-transferred arc plasma torches (25–65 kW), which are operated at high current (usually 400–800 A), lower working voltage (usually 30–80 V) and have higher levels of voltage fluctuation (ΔU = ±5–25 V) [2, 4, 5, 7].
Fig. 9

Voltage–current characteristics of the laminar plasma torch at different gas flow rates for a mixture of 70% nitrogen and 30% argon by volume

Initially, at a relatively low current (from around 60 to 70 A), the arc voltage decreases slightly with increasing current. This is because the arc temperature increases and the arc expands rapidly, so the electrical conductivity averaged over a radial cross-section of the arc increases. As the current increases further, the arc diameter remains approximately constant, and the electric conductivity increases less rapidly than the current. The voltage is approximately constant for a small range of currents, and then increases as the current continues to increase from about 80 A to 165 A. The voltage–current curve has an approximate U-shape over a large portion of its range. This behaviour is opposite to that of conventional direct current non-transferred arc plasma torches with a linear channel structure, such as the Sulzer PTF4 Gun, 3 MB Gun and Praxair SG-100 Gun, which exhibit voltage–current curves with a drooping shape at the same level of output power [4, 5]. Moreover, the rising voltage–current characteristic enables the power supply to maintain an electrical efficiency close to unity. It is worth noting that the same rising voltage–current characteristics can be obtained in other laminar plasma torches that with very different inner channel structures: those of Osaki et al. [38], Pan et al. [14], M. F. Zhukov et al. (2003) [8, 39], Vilotijevic et al. [40] and Wang et al. [41].

Modelling of the Long Laminar Plasma Jet

Computational fluid dynamics modelling was performed to obtain greater understanding of the flow and heat transfer characteristics of the laminar plasma jet. A two-dimensional axisymmetric steady-state modelling approach was applied in this study. The model is constituted by the governing equations of conservation of mass, momentum and energy, and is implemented in the commercial software package ANSYS-Fluent v16.0. The simulations used was the pressure-based solver, the SIMPLE algorithm, and second order upwind differencing. The model assumes that the plasma is in Local Thermodynamic Equilibrium (LTE).

The governing equations are:
$$\frac{\partial }{\partial x}(\rho u) + \frac{1}{r}\frac{\partial }{\partial r}(r\rho v) = 0$$
(1)
$$\frac{\partial (\rho uu)}{\partial x} + \frac{1}{r}\frac{\partial (r\rho uv)}{\partial r} = - \frac{\partial P}{\partial x} + 2\frac{\partial }{\partial x}\left( {\mu_{eff} \frac{\partial u}{\partial x}} \right) + \frac{1}{r}\frac{\partial }{\partial r}\left[ {r\mu_{eff} \left( {\frac{\partial u}{\partial r} + \frac{\partial v}{\partial x}} \right)} \right]$$
(2)
$$\frac{\partial (\rho uv)}{\partial x} + \frac{1}{r}\frac{\partial (r\rho vv)}{\partial r} = - \frac{\partial P}{\partial r} + \frac{2}{r}\frac{\partial }{\partial r}\left[ {r\mu_{eff} \frac{\partial v}{\partial r}} \right] + \frac{\partial }{\partial x}\left[ {\mu_{eff} \left( {\frac{\partial v}{\partial x} + \frac{\partial u}{\partial r}} \right)} \right] - 2(\mu + \mu_{t} )\frac{v}{{r^{2} }}$$
(3)
$$\rho C_{p} \left( {u\frac{\partial T}{\partial u} + \frac{1}{r}\frac{\partial v}{\partial r}} \right) = \nabla \cdot (\kappa_{eff} \nabla T) - 4\pi \varepsilon_{r}$$
(4)
$$\rho \left( {u\frac{\partial k}{\partial x} + v\frac{\partial k}{\partial r}} \right) = \nabla \cdot (\alpha_{k} \mu_{eff} \nabla k) + G_{k} - \rho \varepsilon - Y_{M}$$
(5)
$$\rho \left( {u\frac{\partial \varepsilon }{\partial x} + v\frac{\partial \varepsilon }{\partial r}} \right) = \nabla \cdot (\alpha_{\varepsilon } \mu_{eff} \nabla \varepsilon ) + C_{1\varepsilon } G_{k} \frac{\varepsilon }{k} - C_{2\varepsilon } \rho \frac{{\varepsilon^{2} }}{k} - R_{\varepsilon }$$
(6)

In these equations, u and v are the axial (x) and radial (r) velocity components; ρ, μ, k, Cp, and 4πεr are the plasma density, viscosity, thermal conductivity, specific heat at constant pressure, and radiated power per unit volume of plasma, respectively.

The Renormalization Group k-ε Model (RNG) was used for modelling turbulent viscosity in this study [42]. The RNG theory provides an analytically-derived differential formula for effective viscosity that accounts for low Reynolds-number effects, and an analytical formula for turbulent Prandtl numbers, while the standard k-ε model uses user-specified constant values. These features make the RNG k-ε model more accurate and reliable for a wide class of flows than the standard k-ε model, especially in the case of the laminar plasma jet considered here.

In Eqs. (5) and (6), Gk represents the generation of turbulent kinetic energy due to the mean velocity gradients, and YM represents the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate [42]. The quantities αk and αε, respectively the inverse effective Prandtl numbers for k and ε are both set equal to 1.393. C1ε and C2ε are set equal to 1.42 and 1.68 respectively. The main difference between the RNG and the standard k-ε model lies in the additional term of the turbulent dissipation equation given by:
$$R_{\varepsilon } = \frac{{C_{\mu } \rho \eta^{3} (1 - \eta /\eta_{0} )}}{{1 + \beta \eta^{3} }} \cdot \frac{{\varepsilon^{2} }}{k}$$
(7)
where η0= 4.38, β = 0.012, Cμ= 0.0845. The effective viscosity is given by:
$$\mu_{eff} = \mu + \mu_{t}$$
(8)
$$\mu_{t} = \rho C_{\mu } \frac{{k^{2} }}{\varepsilon }$$
(9)

For the case of laminar flow simulations, Eqs. (1) to (4) were used by setting the turbulent viscosity µt equal to 0 and Eqs. (5) and (6) were removed from the model. The effective viscosity option in the RNG Model was used in the simulation. This allows modelling of the effective turbulent transport variation with the effective Reynolds number (or eddy scale), allowing the model to better handle low- Reynolds- number and near- wall flows [42].

Actually, authors have tried Standard k-ε Model, k-omega Model, Reynolds Stress Model and Spalart–Allmaras Model to simulate this plasma jet. These results list in the supplement files. However, these results are all far away from the experiment observations.

The computational domain is shown in Fig. 10; the diameter of the nozzle exit is 5 mm, and the values of the other boundary conditions are shown in Table 1. The initial flow inlet conditions (AB) were derived from the results of modelling of the internal regions of the laminar plasma torch (Fig. 11) [36], for operation at 25.4 kW (for a total current of 160 A) in 70% nitrogen and 30% argon by volume, with a total flow rate of 14 L min−1. The maximum velocity and temperature at the inlet are respectively 2024 m/s and 16 870 K. The boundary BC is the water-cooled wall of the torch nozzle, for which the thermal boundary conditions is specified by a heat transfer coefficient (hw) of 1.0 × 105 W m−2K−1 and reference cooling water temperature (Tw) of 500 K.
Fig. 10

Schematic of the computational domain of the laminar plasma jet model

Table 1

Boundary conditions of the computational domain

Defined condition

Boundary

T (K)

V (m s−1)

S (mm)

Nozzle exit

AB

Fig. 11b

Fig. 11a

2.5

Nozzle wall

BC

hw (T− Tw)

0

37.5

Freestream

CD

300

10

Freestream

DE

300

400

Symmetry axis

AF

400

Outflow

EF

50

Fig. 11

Boundary conditions at the nozzle exit: a velocity and b temperature. Profiles obtained by a model of the internal region of the laminar plasma torch operating at 25.4 kW (I = 160 A, Q = 14 L min−1 with 70% nitrogen and 30% argon in volume)

The thermodynamic and transport properties of nitrogen and argon mixtures were calculated using the methods presented in references [43] and [44]. The data used in the model were presented in [36]. Figure 12 shows the temperature dependent of specific heat of dry air [45], argon [45] and the mixture of 70% nitrogen and 30% argon used in this work [36]. The model assumes that the discharge environment has the same composition as the working gas (i.e. argon–nitrogen mixture). This assumption significantly simplifies the model and is expected to be reasonable given the relatively small difference in specific heats between the Ar–N2 mixtures used in the model and air for the characteristics of the plasma jet (i.e. temperature < 14,000 K).
Fig. 12

Temperature dependence of the specific heat of dry air [46], argon [45] and the mixture of 70% nitrogen and 30% argon [36] used in this work at atmospheric pressure

Figure 13 shows the velocity and temperature distributions of the plasma jet obtained using the laminar flow model for operation at the output power of 25.4 kW (I = 160 A) using 70% nitrogen and 30% argon. The velocity of the plasma jet plume rapidly decreases downstream of the nozzle exit. The length of the jet for which the velocity remains greater than 1000 ms−1 is about 100 mm. The high temperature jet expands rapidly as it is ejected out of the nozzle exit. The temperature distribution showed a high-temperature vortex region at over 10,000 K very close to the nozzle exit before narrowing to form a uniform and slowly expanding jet. This is consistent with the experimental observation shown in Figs. 3a and 15 of the presence of a bright region close to the nozzle exit.
Fig. 13

Velocity and temperature distributions of the plasma jet predicted by the laminar model

The velocity and temperature distributions presented by the RNG turbulent model are presented in Fig. 14. The results are very similar to those in Fig. 13. The high temperature region at the nozzle exit slightly decreased in size.
Fig. 14

Velocity and temperature distributions of the plasma jet predicted by the RNG turbulent model

The attenuation of axial velocity and temperature along the jet axis obtained using the two models are shown in Fig. 15. The temperature at the torch exit was 16,870 K and decreased rapidly to below 8500 K within 5 mm of the nozzle exit. The attenuation of the axial velocity is less rapid. The RNG model predicts less rapid decreases of axial velocity and particularly temperature than the laminar model in the downstream regions, but the differences between the models are relatively small.
Fig. 15

Attenuation of the axial velocity and temperature along the plasma jet axis and comparing with the experimental observation

Figure 16 showed the turbulent dissipation, turbulent kinetic energy and turbulent intensity distributions. All three quantities are largest at the nozzle exit, where the velocity and temperature are largest. The turbulent energy is rapidly dissipated both radially and axially away from the exit. Similarly, the turbulent intensity continuously decreases along the direction of flow. The distribution of turbulence intensity differs strongly from that of conventional direct-current non-transferred arc plasma torch, in which a very high turbulence intensity occurs at the interface between the expanding plasma jet and the atmosphere [46, 47]. This region of strong turbulence leads to greatly enhanced mixing of the atmosphere into the plasma jet, leading to a rapid cooling of the jet. The absence of such strong turbulent mixing facilitates the formation of the long laminar plasma jets studied in this article.
Fig. 16

Turbulent dissipation (m2 s−3), turbulent kinetic energy (m2 s−2), and turbulent intensity (%) distributions of the plasma jet

Conclusions

This article presented the experimental and numerical study of a novel direct current non-transferred arc plasma torch that can generate different lengths of long laminar plasma jets in ambient air. The results showed that the long laminar plasma jets can be conveniently controlled through the gas flow rate and output power of the equipment. The experimental observations of the plasma jet indicated a high stability in the atmospheric environment. The maximum jet length can reach about 720 mm in air. An increasing voltage current characteristic was obtained under a gas flow rate of 8.5–15 L min−1 and a working current of 60–165 A, for operation with a mixture of 70% nitrogen and 30% argon by volume.

The flow characteristics of the long laminar plasma jet were studied using two-dimensional computational fluid dynamics model that makes use of nozzle data produced by a coupled electromagnetic and fluid dynamic model of the plasma inside the body of the torch. A bright region near the nozzle exit that was observed in the experiments corresponds to a region predicted to be at the temperature of over 10,000 K; the temperature was predicted to rapidly decrease downstream of the bright region. The attenuation of velocity along the torch axis was smaller than that of temperature. The turbulent kinetic energy and intensity were predicted to be highest near the nozzle exit. This is in contrast to conventional plasma torches, in which they are largest in the regions at the interface between the expanding plasma jet and the atmosphere.

Notes

Acknowledgements

The authors are grateful to Prof. Ren-zhong Huang from the Department of New Materials of Guangzhou Non-Ferrous Metal Research Institute for his selfless help with the computer programming. This work was supported by the Natural Key R&D Program of China (Basic Research Project, Grant No. 2017YFB0306104), the Ph.D. Short-term Academic Visiting Program of Graduate School of Xi’an Jiaotong University and National Ph.D. Degree Program of the China Scholarship Council.

Supplementary material

11090_2018_9949_MOESM1_ESM.gif (6 mb)
Supplementary material 1 (GIF 6103 kb)
11090_2018_9949_MOESM2_ESM.tif (4.2 mb)
Supplementary material 2 (TIFF 4324 kb)

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  • Sen-Hui Liu
    • 1
    • 3
  • Shan-Lin Zhang
    • 1
  • Cheng-Xin Li
    • 1
    Email author
  • Lu Li
    • 2
  • Jia-Hua Huang
    • 2
  • Juan Pablo Trelles
    • 3
  • Anthony B. Murphy
    • 4
  • Chang-Jiu Li
    • 1
  1. 1.State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and EngineeringXi’an Jiaotong UniversityXi’anChina
  2. 2.Zhenhuo Plasma Technology Co., LtdChenduChina
  3. 3.Department of Mechanical EngineeringUniversity of Massachusetts LowellLowellUSA
  4. 4.CSIRO ManufacturingLindfieldAustralia

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