Terese Suvorovs

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.

Effect of Geometry on the Melting Rates of Iron Rods Burning in High Pressure Oxygen

The effect of sample geometry on the melting rates of burning iron rods was assessed. Promoted-ignition tests were conducted with rods having cylindrical, rectangular, and triangular cross-sectional shapes over a range of cross-sectional areas. The regression rate of the melting interface (RRMI) was assessed using a statistical approach which enabled the quantification of confidence levels for the observed differences in RRMI. Statistically significant differences in RRMI were observed for rods with the same cross-sectional area but different cross-sectional shape. The magnitude of the proportional difference in RRMI increased with the cross-sectional area. Triangular rods had the highest RRMI, followed by rectangular rods, and then cylindrical rods. The dependence of RRMI on rod shape is shown to relate to the action of molten metal at corners. The corners of the rectangular and triangular rods melted faster than the faces due to their locally higher surface area to volume ratios. This phenomenon altered the attachment geometry between liquid and solid phases, increasing the surface area available for heat transfer, causing faster melting. Findings relating to the application of standard flammability test results in industrial situations are also presented.

Investigation of Burning Aluminum in Oxygen-Enriched Atmospheres through Microanalysis Techniques

Promoted-ignition testing of 3.2 mm diameter aluminum rods in high purity oxygen was performed. The rod and detached drops of both self-extinguished and water quenched samples were examined using scanning electron microscopy and electron probe microanalysis to analyze the physical structure of the sample and gather compositional data. A comparison of the micrographs of self-extinguished and quenched samples reveals clear differences in the extent of melted and re-solidified (unreacted) material and the thickness of the oxide layer, highlighting the effect of cooling rate on the burning system. A qualitative physical model for the burning of bulk aluminum in gaseous oxygen is presented. The model, incorporating a molten drop growth and detachment cycle, is based on an initial heterogeneous burning phase leading to a second phase of combined heterogeneous and homogeneous burning.

Effect of Sample Geometry on Regression Rate of the Melting Interface for Carbon Steel Burned in Oxygen

Promoted-ignition testing on carbon steel rods of varying cross-sectional area and shape was performed in high pressure oxygen to assess the effect of sample geometry on the regression rate of the melting interface. Cylindrical and rectangular geometries and three different cross sections were tested and the regression rates of the cylinders were compared to the regression rates of the rectangular samples at test pressures around 6.9 MPa. Tests were recorded and video analysis used to determine the regression rate of the melting interface by a new method based on a drop cycle which was found to provide a good basis for statistical analysis and provide excellent agreement to the standard averaging methods used. Both geometries tested showed the typical trend of decreasing regression rate of the melting interface with increasing cross-sectional area; however, it was shown that the effect of geometry is more significant as the samples cross sections become larger. Discussion is provided regarding the use of 3.2-mm square rods rather than 3.2-mm cylindrical rods within the standard ASTM test and any effect this may have on the observed regression rate of the melting interface.