Theodore A. Steinberg

The combustion phase of burning metals

Abstract Glassmans hypothesis and burn ratio are examined for their suitability for predicting the phase of combustion of metals. Neither criterion is validated based on either published property values of experimental evidence. Inconsistencies in published property values and definitions are noted. Computer calculations provide a more appropriatd description of the composition of the combustion products and the adiabatic flame temperature of a burning metal at equilibrium. Dissociation temperatures (and product compositions) for 11 metals are computed using a specified quantity of thermal energy and compared with adiabatic flame temperatures.

The solubility of oxygen in liquid iron oxide during the combustion of iron rods in high-pressure oxygen

Abstract The combustion of pure iron rods in oxygen is characterized by excess oxygen in the molten products. The amount of oxygen dissolved in the molten mass exceeds that required for stoichiometric haematite, Fe 2 O 3 , the highest oxidation state for solid iron oxide. Oxygen mass-balance calculations and post-test product analysis suggest that the average oxygen-to-iron molar ratio of the molten oxide product is as high as 2.1 and possibly higher. This corresponds to an increase in oxygen solubility in the molten iron oxide (over that of molten iron metal), which is compatible with the existence of various forms of ferrite ions such as FeO 2 −1 , Fe 2 O 5 −4 , FeO 3 −3 , and Fe 2 O 7 −8 . The presence of this excess oxygen confirms the proposed heterogeneous mechanism for the burning of iron, that is, that primary oxidation takes place at an interface between liquid iron and the molten combustion products containing the excess oxygen.

The combustion of iron in high-pressure oxygen

Abstract The combustion of 0.32-cm-diameter pure iron rods at 6.9 MPa oxygen pressure was investigated. During the upward burning of the sample rods, it was found that there was excess oxygen above the stoichiometric requirement for the formation of the product oxide in the formed molten ball. The excess oxygen in the formed molten ball suggests that the rate limiting step for iron combustion, at 6.9 MPa, is the kinetic reaction at a molten iron core in the ball, and not oxygen intake into the molten ball as previously thought. Glassmans hypothesis as to the phase in which a metal burns was investigated and found to be inappropriate for iron for the pressure considered.

The burning of metals and alloys in microgravity

Abstract Use of high-pressure oxygen systems in space applications requires an understanding of how metals and alloys burn in microgravity. The present work involved burning rods of 2219 aluminum, 316 stainless steel, iron, and titanium, and sheets and meshes of 316 stainless steel in the 2.2-s drop tower at NASA Lewis Research Center. In microgravity, the metals (and alloys) and configurations tested burned vigorously, and the following was observed: (a) the absence of the buoyant force does not cause extinguishment of combustion; the molten ball is well-mixed over the duration of an experiment; (b) the regression rate of the melting interface of the cylindrical rods is significantly greater than in normal gravity; (c) ignition of adjacent materials readily occurs; (d) flammability of sample shapes, for example, thin sheets, which extinguish in normal gravity, is enhanced and samples burn to completion; (e) volatile combustion products are produced, an event that does not occur under similar conditions in normal gravity, (f) as occurs in the normal gravity combustion or iron rods, excess oxygen above stoichiometric requirements is contained in the formed molten ball; and (g) a similar dependency exists in microgravity to that in normal gravity between regression rate of the melting interface and oxygen pressure and rod diameter. Four of the above phenomena (b, c, d, and e) can be attributed to higher temperatures that result from the retention of all the reacting mass in the molten ball.

Review, Analysis, and Hazard Mitigation of the Life-Support Oxygen System on Royal Australian Air Force P-3 Orion Aircraft

To ensure te ongoing safe operation of the Royal Australian Air Force (RAAF) P-3 Orion life-support oxygen system, a system review was completed that included a failure modes and effects analysis combined with an oxygen hazards and fire risk analysis. Though the RAAF P-3 Orion oxygen system has been operational for many years, the results of these analyses clearly identified many deficiencies in the current system configuration, thus demonstrating the value of the formal analysis approach. Design, procedural, maintenance, and material issues were all identified and addressed in the course of this process. This paper provides a brief summary of the analyses performed, the results obtained, risk tables generated, and their use leading to the recommendations for changes incorporated onto RAAF P-3 Orion aircraft that resulted from this work.

Emission spectra of burning iron in high-pressure oxygen

Abstract Emission spectra of burning vertical iron rods in high-pressure oxygen were taken and correlated with the different stages of the burn evolution. By applying the least squares method to the spectral curves, the corresponding equivalent blackbody temperatures were computed. Based on the assumption of a wavelength-independent emissivity between 495 and 780 nm, it was found that the surface-averaged temperatures of the molten iron/iron oxide droplets ranged from a minimal value of ∼ 2500 K to a maximum value of ∼ 3900 K (in 1630 kPa O2) and the temperatures increased with the size (and age) of the droplets.

Instabilities and drop formation in cylindrical liquid jets in reduced gravity

The effects of convective and absolute instabilities on the formation of drops formed from cylindrical liquid jets of glycerol/water issuing into still air were investigated. Medium-duration reduced gravity tests were conducted aboard NASA’s KC-135 and compared to similar tests performed under normal gravity conditions to aid in understanding the drop formation process. In reduced gravity, the Rayleigh–Chandrasekhar Equation was found to accurately predict the transition between a region of absolute and convective instability as defined by a critical Weber number. Observations of the physics of the jet, its breakup, and subsequent drop dynamics under both gravity conditions and the effects of the two instabilities on these processes are presented. All the normal gravity liquid jets investigated, in regions of convective or absolute instability, were subject to significant stretching effects, which affected the subsequent drop and associated geometry and dynamics. These effects were not displayed in reduced gravity and, therefore, the liquid jets would form drops which took longer to form (reduction in drop frequency), larger in size, and more spherical (surface tension effects). Most observed changes, in regions of either absolute or convective instabilities, were due to a reduction in the buoyancy force and an increased importance of the surface tension force acting on the liquid contained in the jet or formed drop. Reduced gravity environments allow better investigations to be performed into the physics of liquid jets, subsequently formed drops, and the effects of instabilities on these systems. In reduced gravity, drops form up to three times more slowly and as a consequence are up to three times larger in volume in the theoretical absolute instability region than in the theoretical convective instability region. This difference was not seen in the corresponding normal gravity tests due to the masking effects of gravity. A drop is shown to be able to form and detach in a region of absolute instability, and spanning the critical Weber number (from a region of convective to absolute instability) resulted in a marked change in dynamics and geometry of the liquid jet and detaching drops.

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.

Thermodynamics and kinetics of burning iron

Macroscopic kinetic analysis of the burning of 0.1 and 0.2-cm-diameter iron rods in pure oxygen at pressures between 0.3 MPa and 10 MPa, and 0.32-cm-diameter iron rods in pure oxygen at pressures between 0.3 MPa and 5 MPa indicates that the kinetic reaction occurs at the phase boundary between the molten oxide product and the liquid iron core. An apparent activation energy of 246.8 kJ/mol Fe(1) is consistent with this analysis. The surface area of the liquid oxide/liquid iron phase-boundary is appropriate for describing the reaction. An enthalpy of reaction of -365.2 kJ/mol Fe(1) at 298K is consistent for the burning of iron. The Langmuir-Hinshelwood-Hougen-Watson mechanism is consistent with the flammability data for iron. In the linear range of that mechanism an appropriate rate equation is: R Fe = 7.05E3exp(-2.9684E4/T)P O2 1/2gm cm-2 s-1.

Geopolymer encapsulation of a chloride salt phase change material for high temperature thermal energy storage

In an effort to reduce the cost and increase the material compatibility of encapsulated phase change materials (EPCMs) a new encapsulated system has been proposed. In the current study a molten salt eutectic of barium chloride (53% wt.), potassium chloride (28% wt.) and sodium chloride (19% wt.) has been identified as a promising candidate for low cost EPCM storage systems. The latent heat, melting point and thermal stability of the phase change material (PCM) was determined by DSC and was found to be in good agreement with results published in the literature. To cope with the corrosive nature of the PCM, it was decided that a fly-ash based geopolymer met the thermal and economic constraints for encapsulation. The thermal stability of the geopolymer shell was also tested with several formulations proving to form a stable shell for the chosen PCM at 200°C and/or 600°C. Lastly several capsules of the geopolymer shell with a chloride PCM were fabricated using a variety of methods with several samples remaining stable after exposure to 600°C testing.