Investigation of the Effects of Shear on Arc Heater Electrodes Using a Modified Mass Loss Model

摘要

In an arc heater, electrons transition from the cathode to the gas being heated, travel a distance of a few inches to several feet, and then enter the anode with high energy. Likewise, positively charged particles leave the anode surface and travel down the arc heater towards the cathode. Along the way, many collisions within the gas take place, causing both ions to be neutralized and new electrons and positive ions to be created. The violent processes of both electrons and ions leaving the electrode surface and their recapture at the complementary electrode causes intensive heating, leading to electrode mass loss due to melting and vaporization. The factors that contribute to mass loss include vaporization (boiling), material removal via shear forces, chemical reactions, evaporation, and ejection of molten material in jets due to pressure effects. To increase electrode life, a magnetic field is applied to cause the arc attachment point to move. For annular electrodes, the arc attachment point is caused to spin, returning to the same point periodically. An analytic model of a moving arc that included the processes of melting, evaporation, and boiling was developed in previous research. In this pseudo one-dimensional model the motion of the arc is synthesized by applying a high surface heat flux in periodic cycles. The present work enhances that model by including mass loss due to shear at the electrode surface. It was found that shear is a viable loss mechanism and can account for the differences between theoretical and experimental mass loss rates observed.