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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 po...
Citations
... Thermal plasma jet is a novel applied energy, which has been widely used. Based on thermal plasma technologies, a new thermal plasma jet with higher jet stability and controllability, larger length-diameter ratio and lower working noise, has been generated and studied for more favorable jet characteristics by some research groups in the past few decades [1][2][3][4][5] . With the favorable jet characteristics, the new thermal plasma jet, named as laminar plasma jet, is more suitable for some high precision applications, e.g. ...
... The jet characteristics of the cascade laminar plasma torch under different working conditions also have been studied experimentally [15][16][17][18][19] . Recently, the experimental characteristics of the plasma jet generated by a spraying plasma torch with cascade structure have been studied and discussed by Senhui Liu etc., [2] . With the experimental studies on the jet characteristics of laminar plasma torches, the properties of laminar plasma torch have been improved and the generation mechanisms of laminar plasma jet have been discussed. ...
For the low costs, numerical simulations are effective methods to reveal the internal mechanism inside thermal spraying plasma torch. Various simulation models for studying the inside or outside characteristics of thermal plasma torches have been built and discussed. However, for revealing the mechanism in the materials processing, more attentions should be paid to building precise models of laminar plasma torch and using these models to reveal the generating mechanism and the flow characteristics. Thus, based on the user-defined function (UDF) and user-defined scalar (UDS) of ANSYS Fluent software, the assumptions, governing equations, boundary conditions and solving method were discussed and a corresponding numerical model of a home-made laminar spraying plasma torch was built firstly. For verifying the effectiveness of the proposed numerical model and studying the influence of the gas components on the arc characteristics, the working conditions and experimental setups were introduced in sequence. Finally, the numerical and experimental results of the home-made laminar plasma torch were obtained and discussed. The study results show that: ¬① The axial temperature of the plasma torch could be divided into three sections along the axis: peak temperature area (10mm < x < 20mm), stable temperature area (20mm < x < 62mm) and decrease temperature area (62mm < x < 95mm). ② The axial velocity of pure nitrogen is much higher than that of pure argon and 50%Ar + 50%N 2 , while that of pure argon and 50%Ar + 50%N 2 has a little difference. ③ The simulated arc voltage trends under different working conditions are in accordance with the experimental arc voltage trends well.
... Laser was used as the heat source in some studies [16][17][18]. Recently, laminar plasma has been developed as a new heat resource based on original turbulent plasma [19,20]. Compared with laser, it has many advantages of higher temperature and good controllability [21]. ...
... The jet length usually increases with increasing 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 [13]. ...
For monitoring the online jet characteristics and improving the corresponding diagnostic accuracy, caused by the complex working environment of arc plasma generation systems, an online diagnostic method of arc plasma jet characteristics based on wavelet transform and linear regression theory was proposed. The wavelet denoising to improve the accuracy of plasma jet characteristics and the linear regression theory to predict the plasma arc voltage characteristics have been discussed. Hence, a comprehensive online diagnostic system of plasma jet characteristics has been designed by integrating the proposed method with LabVIEW virtual instrument technology. To verify the effectiveness of the online diagnostic method and system, the corresponding experiments have been conducted by using a homemade plasma generation system with specified working parameters. Sequence, the experimental results have been analyzed and discussed. The experimental results show that: (1) the proposed online diagnostic method based on wavelet transform and linear regression theory could effectively improve the accuracy and predict the jet characteristics of plasma jets; (2) the online jet characteristics of thermal plasma jet could be monitored by using the corresponding diagnostic system.
... Subsequently, the effect of the carrier gas on the laminar plasma jet and the behavior of the powder particles in the laminar plasma jet were simulated. The simulation was performed using ANSYS Fluent software with the following assumptions [16,17]: ...
... Therefore, the system needed to provide more energy to maintain the arc discharge state. These positive resistance properties were also found in [23][24][25]. The Lorentz force between the arcs and the drag force of the gas reached a relative balance in the OEOF pattern, which resulted in hardly any change in arc length with the increasing current. ...
The enhanced volume of thermal plasma is produced by a multi-arc thermal plasma generator with three pairs of discharge electrodes driven by three directed current power suppliers. Combined with a high-speed camera and an oscilloscope, which acquire optical and electric signals synchronously, the dynamic behavior of different kinds of multi-arc discharge adjusted by the electrode arrangement is investigated. Also, the spatial distributions and instability of the arc discharge are analyzed in four electrode configurations using the gray value statistical method. It is found that the cathodic arcs mainly show a contracting state, while the anodic arcs have a trend of transition from shrinkage to a diffusion-like state with the increase of the discharge current. As a result of the adjustment of the electrode configuration, a high temperature region formed in the center of the discharge region in configurations of adjacent electrodes with opposite flow distribution and opposite electrodes with swirl flow distribution due to severe fluctuation of arcs. The discharge voltage rises with increased discharge current in this novel multi-arc plasma generator. It is also found that anode ablation mainly occurs on the conical surface at the copper electrode tip, while cathode erosion mainly occurs on the surface of the inserted tungsten and the nearby copper.
... The motivation for the current investigation of the reduction of NiO by CHP is based on the following reasons: (a) plasma uses are becoming more prevalent in metallurgical processes, including metal extraction [10,27,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54].(b) the extraction flow sheet of nickel production includes a unit process of reduction of an intermediate product, e.g., NiO, (c) NiO → Ni is a single-step process whereas other metal oxides show multi-step reduction, (d) NiO → Ni reduction process is only slightly exothermic, therefore, can be considered as isothermal, whereas, other metal oxides had contributions to reaction enthalpy, (e) NiO → Ni reduction is irreversible and first order with respect to H 2 . (f) associated with only minor structural changes (g) to check whether there is any effect of stoichiometry on the plasma-metal oxide reaction, (h) to check whether CHP can remove the persistent incubation period. ...
Recently, a new production process of various metals and alloys from their oxides and ores by Cold Hydrogen Plasma (CHP) has been introduced. CHP is produced by using a microwave oven, using less power than the microwave ovens used domestically for cooking food. CHP is very efficient in producing metals and alloys from their oxides because of excited species. These excited species decrease the thermodynamic and kinetic barriers of reduction, making the reduction easier and faster. In the current investigation, nickel has been produced from nickel oxide (NiO) pellets of ~ 2.5 gm to ~ 7.5 gm. The hydrogen flow rate ranges from 70 ml/s to 150 ml/s, and power varies from 600 to 750 W. The time taken for reduction changed between 300 to 1200 s. CHP reduces very fast due to the active oxygen present in it. This faster production of nickel from pellets upto ~ 7.5 gm at such low power opens up the possibilities of upscaling the reduction of NiO by CHP.
... The LPT always generates laminar plasma jet working with a low working gas flow rate. Correspondingly, the laminar plasma jet flows in laminar state with slight air entrainment, resulting in a low working noise (< 90 db), high mean specific enthalpy, high stability and controllability [21][22][23]. Besides, as shown in Fig. 1, compared with the turbulent plasma jet, the laminar plasma jet, which looks like a lightsaber, has a larger length/diameter ratio, leading to a lower axis temperature gradient. However, due to its low working gas flow rate, the mean thermal efficiency of the LPT is always lower than 50% and a segmented anode structure (shown in Fig. 2) is always adopted to suppress the generation of double arc phenomenon, which is always caused by low breakdown voltage between the arc chamber wall and the plasma arc, and long axial length of the inter-electrodes [24,25]. ...
Due to their favorable characteristics, e.g. high temperature, low operating cost and environmental requirements, direct current thermal plasma jets have been widely used. Correspondingly, in order to meet the different requirements of the diverse applications, different thermal plasma torches have been invented and their characteristics have been widely studied. The characteristics of a thermal plasma torch could be decided by its construction and working parameters. Though the influences of some factors on the characteristics of different thermal plasma torches have been experimentally and theoretically studied, there is little study on the influences of different gas flow rates on the characteristics of plasma torch working with two gas injection channels. Therefore, an optimized thermal plasma torch working with two gas injection channels has been proposed and its characteristics have been experimentally studied and discussed in this paper. The design considerations of the proposed plasma torch are discussed firstly. Then the experimental methods and results are introduced and discussed. The experimental results showed that the first gas flow rate nearing the cathode has little influences on the characteristics of the proposed thermal plasma torch while the second gas flow rate nearing the anode influences its characteristics obviously.
... Data on the size of this laminar section given in the literature differ. New experiments [16], [29] show that the size of the laminar flow section can be very large. In [29], the laminar section of the submerged subsonic air jets reaches 80-300 diameters of the channel outlet at Re from 600 to 3000 [29]. ...
... In [29], the laminar section of the submerged subsonic air jets reaches 80-300 diameters of the channel outlet at Re from 600 to 3000 [29]. In [16], laminar plasma jets flowing into the air have a length up to 144 nozzle exit diameters. Returning to our problem, we want to emphasize that the part of the jet considered below is located in the interelectrode space. ...
A numerical study of airflow in a single-phase ac plasma torch is presented. The values of electrical current being considered are up to 10-A rms, and the ac frequency is 50 Hz. The electric and gas-dynamic parameters of the plasma torch are efficiently simulated using the model based on the Navier-Stokes equations for compressible medium and the reduced Maxwell equations. The difference in the behavior of parameters in the channel and jet is demonstrated and discussed. The effect of decreasing the observed maximum value of the flow temperature with decreasing the flow rate is shown. An explanation of this effect and an analysis of the gas-dynamic patterns of cold flow and flow with the ac discharge are presented in the following article of the series.
... Previous studies on laminar plasma spray have mainly focused on ceramic coatings [13][14][15][16]. However, the behavior of metal feedstock in the laminar plasma jet still remains unclear. ...
... A numerical simulation of the plasma jet is also carried out to model the spraying process. The composition of the plasma jet in this study is nitrogen-argon plasma with 70% nitrogen and 30% argon [13,19]. The simulation of the plasma jet is based on the following assumptions: (1) the plasma flow is laminar and quasi-steady; (2) the plasma jet operates in local thermal equilibrium (LTE) state and is optically thin to the extent that the radiation is negligible; (3) the heat and mass transfer properties of the plasma jet are temperature-dependent; (4) the electric field near the nozzle exit is negligible; (5) the terms of the viscous dissipation and pressure work in the energy equation are negligible due to the small Mach number; (6) the properties of the mixture of ambient air and plasma gas follow the volume mixing law. ...
A stable laminar plasma jet with a jet length of above 600 mm was adopted to deposit molybdenum coatings to investigate the behavior of high-melting point metal, molybdenum, and particles during laminar plasma spraying process. The temperature, velocity, and species distribution of the plasma jet were calculated by numerical simulation. In the experiment, the temperature and velocity distribution of the in-flight particles were measured, and the microstructure and properties of the coatings were analyzed. Combining the results of the simulation and experimental results, the deposition behavior and oxidation mechanism of the coatings prepared at the spray distance from 200 mm to 400 mm were discussed. The results indicate that both the laminar plasma jet and injected particles exhibit high temperature and low velocity, and low temperature and velocity gradients. The microstructure of the coatings shows a high similarity and hardly changes when the spray distance exceeds 250 mm. When the spray distance is 200 mm, post-deposition oxidation occurs due to the heating effect of the long plasma jet on the substrate. In contrast, when the spray distance is longer, the particles undergo severe in-flight oxidation, and the oxide formed is uniformly distributed in the coating improving the hardness from 500 HV0.3 to 700 HV0.3.
... An APS-PVD method is employed in this work by using a novel long laminar plasma torch under an the atmospheric environment [11][12][13]. The maximum length of the plasma jet is about 1000 mm in an atmospheric environment without any auxiliary devices [14]. This method may provide a new opportunity to obtain advanced microstructures of thermal barrier coatings in an atmospheric environment [15]. ...
Currently, the self-shadowing effect of impinging particles is recognized as a vital factor to form columnar-like coating in the manufacture of thermal barrier coatings. Most of these quasi-columnar coatings are usually prepared under a very low-pressure condition. This paper investigates a novel quasi-columnar yttria stabilized zirconia (YSZ) coating using an atmospheric plasma spray-physical vapor deposition method. The microstructures of the coating present a quasi-columnar structure that is distributed along the cross-section of the coating within certain intervals with a large number of cluster-like structures on the top surface of the coating. A lower particle velocity that contributes to the generation of a mass of vapor YSZ materials is studied via experimental and numerical analyses and these results are compared with other current plasma spray methods. The mechanism of the self-shadowing effect from impinging particles that leads to the formation of a quasi-columnar feature at the boundary layer of the substrate is demonstrated by a three-dimensional numerical simulation and experimental observation. Furthermore, the hybrid growth model of the vapor and droplet co-deposited coating is clarified in this paper.
