Douglas W. Stamps

Gaseous hydrocarbon-air detonations

Abstract Detonation cell width measurements were made on mixtures of air and methane, ethane, dimethylether, nitroethane, ethylene, acetylene, propane, 1,2-epoxypropane, n-hexane, 1-nitrohexane, mixed primary hexylnitrate, n-octane, 2,2,4-trimethylpentane, cyclooctane, 1-octene, cis-cyclooctene, 1,7-octadiene, 1-octyne, n-decane, 1,2-epoxydecane, pentylether, and JP4. Cell width measurements were carried out at 25 and 100°C for some of these fuelair mixtures. For the stoichiometric alkanes, alkenes, and alkynes, there is a very slight decrease in detonation cell width with increasing initial temperature from 25°C to 100°C, although the differences are within the experimental uncertainties in cell width measurements. Also within the uncertainty limits of the measurements, there is no variation in detonation cell width with increase fuel molecular weight for n-alkanes from ethane to n-decane. Molecular structure is found to affect detonability for C8 hydrocarbons, where the saturated ring structure is more sensitive than the straight-chain alkane, which is more sensitive than the branched-chain alkane. Unsaturated alkenes and alkynes are more sensitive to detonation than saturated alkanes. However, the degree of sensitization decreases with increasing molecular weight. Addition of functional groups such as nitro, nitrate, epoxy, and ethers is found to significantly reduce the detonation cell width from the parent n-alkane. Nitrated n-alkanes can be more sensitive than hydrogenair mixtures. The increase in sensitivity of epoxy groups appears to be related to the oxygen to carbon ratio of the molecule. A numerical model, using a simplified ZND analysis and a detailed chemical kinetic reaction mechanism, was used to interpret the experimental results. The model indicates the effect that each factor—fuel molecule size, fuel structure, initial temperature, bond saturation, and inclussion of different functional groups—has on the computed induction length under detonation conditions.

A heuristic model of turbulent mixing applied to blowout of turbulent jet diffusion flames

Abstract A phenomenological study has been conducted on jet flames near blowout for the purpose of determining the blowout mechanism. The authors show the successful blowout correlation of Broadwell et al. [ Twentieth Symposium (International) on Combustion , 1984, p. 303] can be derived from the assumptions of Vanquickenborne and van Tigglen [ Combust. Flame 10:59 (1966)], namely, that blowout is a competition between the local premixed turbulent flame speed and the local flow velocity. The authors argue that the role of coherent, large-scale, rotational structures found in jet turbulence is to enhance the turbulent flame speed near blowout. Experiments were conducted which show that nearly the entire cross-section of the jet is combusting in a premixed flame near blowout. This is distinct from a lifted flame that combusts only near the outer edge of the jet. The length and time scales used in the derivation of the blowout mechanism are compared with those observed in the experiments and found to be consistent with the data.

The influence of initial pressure and temperature on hydrogen-air-diluent detonations☆

Abstract We have studied the influence of pressure and temperature on the detonability of hydrogen-air-diluent mixtures diluted with steam or carbon dioxide. Detonation cell width measurements have been obtained from experiments conducted in a 0.43-m-diameter heated detonation tube. Calculations from a Zeldovich-von Neumann-Doring (ZND) model of a detonation with a detailed chemical-kinetic reaction mechanism for hydrogen oxidation are used to correlate the data. The data show a significant reduction in the ability of a diluent (excess air or hydrogen, carbon dioxide, or steam) to inhibit a detonation as the temperature is increased from 293 to 373 K. Only a small decrease in the cell width is observed with increasing pressure between approximately 1 and 3 atm for hydrogen-air mixtures diluted with steam or excess air. For conditions beyond which data exist, calculations based on the model yield results that indicate similar detonabilities of all mixtures considered at low initial pressures or high initial temperatures. Additionally, these results indicate minima in the cell width for variations in the initial pressure and temperature. The cell minima represent approximately the location of a change in a rate-limiting mechanism corresponding to the extended classical second-limit criterion.

Unsteady three-dimensional natural convection in a fluid-saturated porous medium

Natural convection in a cube of fluid-saturated porous medium having a constant temperature top and bottom is studied numerically. In the first of two special cases considered, the vertical sides are insulated. In the second case, heat is transferred through the vertical sides of the cube. Three distinct flow patterns are identified depending on the rate of heat transfer and the Rayleigh number

High-temperature hydrogen combustion in reactor safety applications

In this paper the effect of elevated temperature on the limits of the various modes of combustion of hydrogen-air-steam mixtures is reviewed. The modes include spontaneous combustion, diffusion flames, deflagrations, and detonations. The existing data on high-temperature hydrogen combustion are reviewed, areas where uncertainties exist are identified, and the importance of these uncertainties are discussed with respect to reactor safety for four different accident scenarios.

Internal Pressure Loads Due to Gaseous Detonations

The internal loading of structures and confinements by gaseous detonation is studied using a multidimensional strong-shock physics code. Hydrogen-air-steam mixtures are used in calculations to show phenomena that apply qualitatively to any detonable gaseous fuel-oxidant-diluent mixture. Several variables are considered with respect to loading: (a) inert layers of various thicknesses; (b) deflagration-to-detonation transition(DDT) location as compared with direct initiation; and (c) some variations in geometry or confinement. Relatively thin inert layers are shown to increase the peak reflected shock pressure over that which would occur if the inert layer were not there. Inert layers may also increase impulse under some circumstances. DDT increases peak reflected pressures over those seen for direct initiation because of precompression of unburned gases. DDT may also increase impulses. Peak reflected pressures and impulses are greater in edges and corners than on flat surfaces. Internal obstruction tends to randomize the energy in a detonation wave, decreasing the impulse on structures, and allowing the pressure to equilibrate more rapidly than if there were no obstruction.

Analyses of the thermal hydraulics in the NUPEC 1/4-scale model containment experiments

The CONTAIN code was used to predict the helium concentrations, gas temperatures and pressures, and wall temperatures of four experiments performed in the NUPEC 1/4-scale model containment. These experiments investigated the thermal-hydraulic effects of helium and steam source flow rates, source elevation, and internal water sprays. Two CONTAIN flow solvers and two nodalization schemes were assessed. One NUPEC test, International Standard Problem 35, was investigated in detail, including the pretest heating phase. The thermal hydraulics of this test were dominated by internal water sprays. A modeling approach based on the assumption that the water sprays generated a large air vortex yielded the best results. Reasons for deviations between the predictions and data are suggested based on experimental uncertainties, different analysis methods, and nodalization schemes.

Pressure rise generated by the expansion of a local gas volume in a closed vessel

Experiments were conducted to determine the pressure rise that results from either the combustion of a localized gas volume or the expansion of a pressurized gas volume adjacent to an inert gas in a closed vessel. The experiments consisted of either pressurized air or the combustion of stoichiometric and fuel-lean hydrogen–air mixtures compressing an inert gas. The pressure rise in the inert gas was measured as a function of either the volume fraction or the initial pressure of the expanding gas. Helium, nitrogen, air and carbon dioxide were tested to explore the effect of inert gas heat capacity on the pressure rise. The final pressure of the inert gas increased with the volume fraction and initial pressure of the expanding gas, and was influenced to a lesser extent by the heat capacity of the inert gas. A model was assessed using the experimental data, and the theoretical results were consistent with the observed trends. This model and other published models were assessed and compared using prior data for localized gas combustion surrounded by an inert gas and the partial combustion of homogeneous methane–air mixtures.

Unsteady thermocline degradation in a fluid-saturated, porous medium

Abstract A numerical model is developed to describe unsteady, three-dimensional, natural convective flows in a fluid-saturated, porous medium having a rectangular volume with impervious walls and finite heat transfer at the boundaries. The model is used to predict the transient decay of a thermocline in a packed bed during a period of stagnation in which there is zero net flow and no energy input into the bed. The computed results compare favorably with experimental data from a packed bed consisting of air and natural stone of mixed sizes and irregular shapes. The results show an upward shift in the position of maximum temperature along the vertical centerline of the bed and confirm the important influence of internal convection on the process. The results also demonstrate that a purely diffusive model would be incapable of a reliable predication. Further, the recognition of finite heat transfer rates at the boundaries is shown to be a significant factor in improving the predictive capability of the model.

A thermal-hydraulic model for catalytic recombiners

Abstract A general analytical model was developed to predict the thermal-hydraulic behavior in box-type catalytic recombiners of different sizes and configurations. The fluid mechanics of the recombiner was modeled as flow through a chimney, which resulted in a modified form of the classic chimney equation to predict the exit gas velocity and flow rate. The thermal behavior of the recombiner was modeled using the transient form of the energy equation for reacting flow. The model was assessed using data from recombiners developed by the NIS Ingenieurgesellschaft Company (NIS), Siemans, and Atomic Energy of Canada Limited. Good agreement was obtained between the model and experimental data for the time-dependent hydrogen concentration in the test facility and the capacity of the recombiner in terms of the hydrogen recombination rate, both key parameters in the analyses of accidents in nuclear power plants. The analytical model could be reduced to the form of an empirical correlation developed for the NIS recombiner under simplifying conditions.