Convection in vertical high‐pressure mercury arcs

Convection in wall‐stabilized high‐pressure arcs is found to be highly sensitive to the relative material properties of the discharge gases. A method has been found to experimentally determine net‐radiative‐emission coefficients that are consistent with more reliably calculated electrical and thermal conductivities. The electrical conductivity of mercury arcs obtained using the electron scattering cross section for mercury derived by Rockwood gives better agreement with experimental temperature profiles than does that obtained by use of McCutchen’s cross section. Using these material properties with a theoretical convection model, good agreement was obtained with measured arc‐temperature profiles in the midplane, with the conical appearance at the bottom of the vertical arc and with the electrical properties. For 18‐mm‐i.d. walls and mercury pressures up to 13 atm, the reduction in radiation found for high mercury pressures was found to be caused by self‐absorption and not by an increase in radial thermal...