Experimental and theoretical investigation of high-pressure arcs. I. The cylindrical arc column (two-dimensional modeling)

The properties of the free-burning arc column are studied for ambient pressures of 0.1 MPa (i.e., atmospheric) to 10 MPa for applications in underwater welding and cutting as well as arc discharge lamps. The influence of transverse magnetic fields is studied in Part II. A DC current of 50-100 A is applied to an argon discharge with a conical tungsten cathode and a plane water-cooled anode which are separated by several millimeters. The electrical properties are measured, and the temperature distribution is determined by spectroscopic means utilizing a two-dimensional charge-coupled device (CCD) sensor. A self-consistent numerical solution of the conservation equations yields the temperature, velocity, pressure, and current distributions. The predicted arc temperatures agree well with the measured temperature distributions. An analysis of the conservation equations shows that the arc column becomes radiation dominated with increasing pressures resulting in small temperature gradients within the column and large gradients at the boundaries. It is found that a net emission coefficient might be used to account for the radiative heat transfer in the investigated parameter range. The arc constricts due to increased convective cooling especially at the cathode, while temperatures and velocities are decreasing. The power expended in the column scales approximately with the square root of the ambient pressure in line with the radiation dominance, whereas the voltage drop across the electrode sheaths exhibits no pressure dependence for a given current.