Plasma Thermal Conductivity Research Articles

Study on Thermophysical Properties of Arc Plasma for Melting Magnesium Oxide Crystals at Atmospheric Pressure

The thermodynamic and transport properties of magnesium oxide crystal arc plasma have been researched under local thermodynamic equilibrium in this paper. The pure CO2 plasma in the arc initiation stage and Mg-CO mixtures plasma in the stable melting stage were selected. The parameter-variation method combined with Levenberg–Marquardt algorithm (PVM-LMA) is used to solve the plasma equilibrium compositions model established by mass action law from higher to lower temperature in sequence. Taking Mg50%-CO50% plasma as an example, the plasma number density of 7500 K is calculated according to 8000 K. The results show that the PVM-LMA algorithm has the advantages of fast and high precision. The comparisons to the results of pure CO2 in previous literature are displayed and our work shows better agreement with theirs. The results of Mg-CO mixtures indicate that the chemical properties of Mg atoms are more active and easier to ionize, which can effectively improve the electrical conductivity and thermal conductivity of plasma and reduce its viscosity.

Metallurgy and Mechanism of Underwater Wet Cutting Using Oxidizing and Exothermic Flux-Cored Wires.

This paper considers the metallurgical processes of dissociation, ionization, oxidation, deoxidation, and dissolution of oxides during underwater wet cutting. A multiphase mechanism of underwater wet cutting consisting of working and idle cycles of the electrical process in a pulsating vapor gas bubble is proposed. A model of arc penetration into metal due to metal oxidation and stabilization of the arc by the inner walls of a narrow kerf is proposed. For underwater cutting of 10 KhSND, 304L steel, CuAl5, and AlMg4.5Mn0.7 alloy, we provide a principle of modeling the phase composition of the gas mixture based on high oxygen concentration, improving ionization, enthalpy, heat capacity, and thermal conductivity of plasma through the use of a mixture of KNO3, FeCO3 and aluminum. The method of improving the thermophysical properties and ionization of plasma due to the exothermic effect when introducing Fe3O4, MoO2, WO2 oxides and Al, Mg, Ti deoxidizers is proposed. Although a negative effect of refractory slag was revealed, it could be removed by using the method of reducing surface tension through the ionic dissolution of refractory oxides in Na3AlF6 cryolite. In underwater cutting of 10 KhSND and 304L, the steel welding current was 344–402 A with a voltage of 36–39 V; in cutting of CuAl5 and AlMg4.5Mn0.7 alloy, the welding current was 360–406; 240 A, with a voltage of 35–37; 38 V, respectively, with the optimal composition of flux-cored wire: 50–60% FeCO3 and KNO3, 20–30% aluminum, 20% Na3AlF6. Application of flux-cored wires of the KNO3-FeCO3-Na3AlF6-Al system allowed stable cutting of 10KhSND, AISI 304L steels, and CuAl5 bronze with kerf width up to 2.5–4.7 mm.

The Effects of Graphite Particles on arc Plasma Characteristics

The interaction between graphite particles and argon plasma in the arc torch is investigated by numerical simulations. The addition of carbon vapor improves the specific heat capacity, electrical conductivity and thermal conductivity of plasma, and decreases its viscosity. It is important to note that the changes in the thermodynamic and transport properties of the plasma substantially affect the arc plasma temperature and the spatial distribution of the carbon vapor concentration. As the graphite particle feed rate increases, the arc will be continuously contracted and the arc electric current density will be increased. The carbon vapor enhances the plasma electrical conductivity, but the heat absorption by the particles reduces the temperature of the plasma, eventually leading to decreased the electrical conductivity. Both result in ascent of the electric field of the arc, so that increase the arc voltage. In addition, the heat flux radial distribution of radiation-absorption of the particles is much less than the thermal conduction, but the particles near the wall absorb radiation from arc region, so that reduce energy loss of the radiation of the arc column.

Spatially resolved behavior of laser-produced copper plasma along expansion direction in the presence of static uniform magnetic field

We report on the spatially resolved optical emission spectroscopic study of laser-produced copper plasma in the presence of static uniform magnetic field in air ambient at atmospheric pressure. The response of copper atomic/ionic lines to magnetic field along the axial direction of plasma is different. It is attributed to the difference in populating process (electron impact excitation and recombination) of each transition. In the present work, we introduced air pressure to calculate the stopping radius and found it to be around the distance at which the intensity is pronounced. The electron density varied as ne = 9.2z−0.33 without magnetic field and in the presence of 0.3 T magnetic field, it varied as ne = 7.9z−0.27. The electron temperature variation with distance from the target in the absence and presence of magnetic field is found to be Te = 1.1z−0.23 and Te = 0.9z−0.18. The electron density and temperature decay slowly along the plasma expansion direction in the presence of magnetic field. It is due to magnetic confinement of plasma. We demonstrated that the thermal conductivity of plasma is enhanced in the presence of magnetic field. From the spatial evolution of the electron density and temperature, we estimated the approximate dimension of the core and tail region of the plasma and found an increase in the core dimension in the presence of magnetic field. The increase in core dimension is in agreement with the intensity variation of ionic line. It is attributed to an increase in heat transfer due to an increase in thermal conductivity in the presence of magnetic field. The present work may help optimize the distance from target to enhance spectral line intensity in optical emission spectroscopy in the presence of magnetic field.

Finite Element Study of Influence Factors on Thermal Conductivity of Plasma Sprayed Zirconia Coatings Based on Digital Image Processing

Combining digital image processing with finite element mesh generation,finite element models based on actual microstructures of plasma sprayed zirconia coatings were built.By employing finite element method in conjunction with Fourier’s equation,the apparent thermal conductivity of zirconia coatings affected by defects,in-cluding pores and cracks were calculated.For comparison,the coating’s thermal conductivity was measured by the la-ser pulse method.The difference between values of the finite element method and experimental results are told to ana-lyze effects of defects and splat interfaces on the thermal conductivity.The results show that splat interfaces are as equally important as defects in defining the thermal conductivity of plasma sprayed coatings in the spray direction.