Fluid-Dynamic Effects, Including Turbulence, on a High-Pressure Discharge
We have been studying the stabilization of discharges by flow phenomena for a number of years, and although more interested in molecular gas discharges as typified by the CO2-laser, broad classifications must be introduced in order to discuss relevant phenomena. The first and perhaps most important classification relates to the existence of negative ions and, while our work has been with electron-attaching gases, we shall also mention non-attaching gases such as nitrogen and the inert gases. Next we distinguish between parallel flow and cross flow as they pertain to the direction of the overall motion of the fluid with respect to the conventional motion of the electrical current. In parallel flow the movement is coaxial and we consider flows going both from anode to cathode (normal mode) and from cathode to anode (reverse flow). Turbulence generating grids are located upstream of the electrodes as shown In Fig. 1, except for the reverse flow where they become ineffective. Because the electrodes are immersed In the flow, the anode is typically made of an array of pins, or a pin-rake, supported in some suitable streamlined fashion. On the other hand, the cathode is a screen or some other device which presents low blockage to the main flow while serving as an electrical “flat-plate”. The gas pressures can be said to be moderate to high although In our own work we operate exclusively near one atmosphere; flow rates are subsonic and intercavity volumes large. Part of our effort has been to vary Interelectrode spacing and to exchange anode pins for anode wires spanning the cross-section.
KeywordsVortex Convection Foam
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