An Investigation of Regression Rate of the Melting Interface for Iron Burning in Normal Gravity and Reduced Gravity

This paper investigates the causes of increased regression rates of the melting interface for metals burning in reduced gravity. Promoted ignition tests have been conducted for 3.2-mm diameter iron rods during a transition from normal gravity to reduced gravity. Immediately upon transition to a reduced-gravity environment, a change in regression rate of the melting interface was evident. The rate was consistently 1.75 times higher in reduced gravity than in normal gravity. The sudden increase in regression rate of the melting interface indicates that it is due to a change in the geometry of the molten ball, rather than higher temperatures. A one-dimensional, steady state heat transfer model was developed, correlating regression rate of the melting interface to surface area of the solid/liquid interface. Evidence is presented suggesting that (a) the solid/liquid interface adopts a “dome” shape in reduced gravity, and (b) that this causes an increase in regression rate of the melting interface directly proportional to the increase in surface area of the solid/liquid interface.