J. Gregor

Effect of arc power and gas flow rate on properties of plasma jet under reduced pressures

DC plasma torch with argon-water stabilization of are was attached to vacuum chamber, in which pressure was varied from atmospheric down to 4kPa. Properties of the plasma jet were strongly affected by plasma generating conditions. Influence of plasma generation parameters, namely chamber pressure, are power and plasma gas flow rate on temperature and velocity profiles in plasma jet were studied. Present the measurements were performed using enthalpy probe connected to mass spectrometer. Such arrangement allows simultaneous measurement of the plasma temperature and velocity as well as composition of the plasma gas.

Theoretical analysis of the influence of diffusion in free jet of hot gas mixture

The theoretical analysis of the influence of diffusion on the distribution of mass fractions in free jet of hot gas mixture is based on the vector form of the continuity equation, including the diffusion member. Measured and computed quantities at the output of the are heater (temperature profile, composition, thermodynamic and transport properties of the used gas mixture) are used as the initial conditions. The influence of diffusion is analyzed using the measured temperature and velocity fields in the cross-sections of the jet along thez-axis. The approximation of radial dependencies of temperature and velocity by Gaussian function makes possible the integration in radial direction. Consequently, the two-dimensional problem in cylindrical coordinates can be transformed into the one-dimensional one. Solving the complete continuity equation, the relations for the distribution of mass fractions can be derived, including the components normally present in the surrounding environment (argon and water vapour in air).

The role of radiation losses in high-pressure blasted electrical arcs

The paper deals with experiments carried out on an arc heater where the electric arc is stabilised by flowing working gas. Measured quantities (especially arc current, voltage drop, gas flow rate, and energy loss) serve as input data for a mathematical model of the arc inside a cylindrical anode channel. Previously, the losses of cathode and anode spots were assumed to be negligible in comparison with the total loss. In the new sets of experiments, a modular structure of the arc heater has made it possible to separate the losses of anode and cathode from the energy losses of the arc itself. Furthermore, the losses caused by radial conduction have been introduced into the model. The most significant change of the model concerns the computation of radiation losses of the arc. In the original model, radiation losses were taken as a portion of the total input power. In the modified model, the radiation loss is expressed using a theoretically calculated net emission coefficient of argon (by V. Aubrecht and M. Bartlova). This approach is possible due to a more precise determination of the arc net energy loss which results in flatter radial temperature profiles. Axial distribution of energy loss for the original and modified model is given in figures.

Investigation of Hot Gas Mixture Free Jet

Abstract The analysis of individual species of a hot gas mixture in a free jet distribution, is based on the vector form of the continuity equation, including the diffusion member, and on the momentum equation. The measured distributions of temperature and axial velocity in cross-sections of the free jet, together with thermodynamic and transport properties of working gas are used in a designed process of calculation. By means of approximation of temperature and velocity radial profiles by Gaussian functions, the two-dimensional problem is transformed into the one-dimensional task. The designed method is applied on the cold region of the jet generated by a hybrid water stabilised plasma torch with argon gas added into the chamber. In this cold region (T<2500 K), rather precise measurement of temperature and velocity can be carried out using rather simple methods (thermocouples, cooled Pitot tube). By the derived mathematical-physical model, the distribution of mass fractions of individual species of the working gas mixture is computed, and the influence of velocity component and turbulence on this distribution is studied. During the calculation, axial dependencies of crosssection, axial velocity, and the turbulence coefficient in the free jet are obtained.

Experimental investigation of hot gas mixture free jet

The distribution of mass fractions of individual species in the working gas mixture is computed, and the influence of radial component of velocity and of turbulence on this distribution and on the velocity field in the cross-section of the jet is studied. The jet is generated by a hybrid water-stabilized are torch. An admixture of argon is added at the input of the are heater.