Louis A. Gritzo

Guidance on risk analysis and safety implications of a large liquefied natural gas (LNG) spill over water.

While recognized standards exist for the systematic safety analysis of potential spills or releases from LNG (Liquefied Natural Gas) storage terminals and facilities on land, no equivalent set of standards or guidance exists for the evaluation of the safety or consequences from LNG spills over water. Heightened security awareness and energy surety issues have increased industrys and the publics attention to these activities. The report reviews several existing studies of LNG spills with respect to their assumptions, inputs, models, and experimental data. Based on this review and further analysis, the report provides guidance on the appropriateness of models, assumptions, and risk management to address public safety and property relative to a potential LNG spill over water.

Measurement of visible and near-IR optical properties of soot produced from laminar flames

This study describes the measurements of the dimensionless extinction constant, K e , of soot in the visible and IR spectrum using the National Institute of Standards and Technology Large Agglomerate Optics Facility. Soot was produced using a 11 mm i.d. laminar diffusion flame burner fueled with acetylene and ethene. Light extinction measurements were performed using light sources at 543.5, 632.8, 856, 1314, and 1565 nm. The mean values of present measurements of K e range from 7.95 to 10.0. These unique experiments provide accurate values of K e to be used for measurements of soot concentration and temperature in the IR spectrum. These measurements represent the first fuel-specific data available in the near-IR spectrum. The measured K e values for all wavelengths are significantly larger than values calculated using reported values of the refractive index and the Rayleigh theory. Transmission electron microscopy and optical microscopy analyses were used to analyze soot morphology and aerosol properties to estimate the influences of beam shielding and light scattering on the observed variations of K e .

Measurement of soot optical properties in the near-infrared spectrum

Abstract The dimensionless extinction constant, K e , was measured using the NIST Large Agglomerate Optics Facility (LAOF) for soot produced from acetylene and ethene flames. Measurements were performed simultaneously using light sources at 632.8 and 856 nm. The experiments at 856 nm represent the longest wavelength for which accurate extinction measurements have been performed for soot. The mean values of present measurements of Ke at 632.8 nm for the acetylene and ethene soot are 8.12 ± 0.59 and 9.65 ± 0.54, respectively. For acetylene, the mean value of K e measured at 856 nm was 8.83 ± 0.69, whereas the mean value for ethene at the same wavelength was 9.35 ± 0.51. The reduction in discrepancy for the fuels between 632.8 and 856 nm may be related to beam shielding effects. As in the case of 632.8 nm, the measured K e values for 856 nm are significantly larger than values calculated using traditional methods. The present measurements provide a more reliable value of K e for use in optical-based soot diagnostics.

Soot Scattering Measurements in the Visible and Near-Infrared Spectrum

Scattering to extinction cross-section ratios, {rho}{sub se} were measured using the NIST Large Agglomerate Optics Facility for soot produced from ethene and acetylene laminar diffusion flames. Measurements were performed using light sources at 543.5 nm, 632.8 nm and 856 nm. The average scattering to extinction cross-section ratios for these wavelengths are equal to 0.246, 0.196, and 0.196 for ethene and 0.316, 0.230, and 0.239 for acetylene. The 856 nm measurements represent the longest wavelength for which accurate scattering measurements have been performed for soot. The size distribution and fractal properties of the two soots were determined to assess the effects of limited acceptance angle range, finite size of the sensor, and departure from cosine response on the uncertainty in the measurement of {rho}{sub se} The expanded relative uncertainty (95% confidence level) was found to be {+-}6% at the two visible wavelengths and {+-}8% at 856 nm. Both the magnitude and wavelength dependence of {rho}{sub se} for the present experiments are significantly different from those reported by Krishnan et al. for overfire soot produced using a turbulent flame. The results are compared with the predictions of fractal optics.

Coupling of Large Fire Phenomenon with Object Geometry and Object Thermal Response

The effect of an object in or near a large fire on the physical pro cesses which result in the heat flux from the fire is defined by the object geometry and temperature, and therefore the fire phenomena and the object physical states can be coupled. Two primary modes of coupling, radiative and convective, and their relative influence on heat flux, are investigated using observations from ex perimental data and numerical simulations. Radiative coupling occurs when a comparatively cold object reduces the incident heat flux (by up to 65%) due to radiative cooling of nearby media. Convective coupling includes: (1) changes in the geometry of the flame zone, and (2) object-induced turbulence which alters and often enhances the flow, mixing, and, hence, combustion processes within the fire. Increases in the heat flux approaching a factor of three have been observed due to these phenomena.

Thermal Measurements from a Series of Tests with a Large Cylindrical Calorimeter on the Leeward Edge of a JP-8 Pool Fire in Cross-Flow

As part of the full scale fuel fire experimental program, a series of JP-8 pool fire experiments with a large cylindrical calorimeter (3.66 m diameter), representing a C-141 aircraft fuselage, at the lee end of the fuel pool were performed at Naval Air Warfare Center, Weapons Division (NAWCWPNS). The series was designed to support Weapon System Safety Assessment (WSSA) needs by addressing the case of a transport aircraft subjected to a large fuel fire. The data collected from this mock series will allow for characterization of the fire environment via a survivable test fixture. This characterization will provide important background information for a future test series utilizing the same fuel pool with an actual C-141 aircraft in place of the cylindrical calorimeter.

Estimates of the Extent and Character of the Oxygen-Starved Interior in Large Pool Fires

Based on data from large pool fire experiments and computational fire field model simulations, the size, shape, and character of the oxygen-starved interior in large pool fires is estimated. In the interior of the fire and near the pool surface, low average and low mean deviation temperatures were noted in experimental data for low wind conditions. These trends tend to indicate the presence of a non-combusting region. Using average and mean deviation temperature distributions (supplemented by heat flux measurements) from several data sets, the spatial extent of the vapor dome is estimated for a range of wind conditions. These estimates are compared with fire field model results of temperature and fuel/air concentration distributions. Predicted and measured temperature trends, supported by heat flux data, illustrate the importance of object placement within the fire during system fire survivability testing. The presence of this region also supplements conventional pool fire representations which are based on a continuous flame zone which extends to the pool surface.

A Dilute Spray Model for Fire Simulations: Formulation, Usage and Benchmark Problems

The focus of this work is to develop a two-phase spray model for application to unsteady fire simulation for the dispersion of dilute liquid fuel or fire suppressant sprays. The model is based on a stochastic separated flow (SSF) approach for which droplet transport equations are integrated in time to account for mass, momentum and energy transfer to the liquid phase. Turbulence models for parcel and sub-parcel droplet dispersion, spray breakup and spray collision are also developed and implemented. Two-way coupling between the liquid spray and the gas phase is accomplished through a numerical sub-cycling procedure. A strategy plan for spray model verification and validation is summarized and results presented for selected cases. The problems examined thus far indicate that the approach provides a robust and accurate means to solve dispersed phase spray transport problems for application to fire phenomena.

in situ sampling and transmission electron microscope analysis of soot in the flame zone of large pool fires

To assess assumptions invoked in experimental optical techniques and fire field model heat transfer calculations, and to provide additional insight into soot formation, transport processes, and oxidation processes, soot samples were obtained within the flame zone of 1 m and 5 m JP-8 pool fires and studied using a transmission electron microscope (TEM) to determine primary particle size and aggregate structure. These studies are of particular interest because previous works have been limited to smaller flames or the overfire region of large fires. The results show primary mean particle sizes of 38.8 nm with a standard deviation of 15.6 nm for the 1-m fires and 43.8 nm with a standard deviation of 23.8 nm for the 5-m fires. Particles between 100 and 150 nm in diameter were only observed in the 5-m fires. Soot was present in the form of wispy-chain aggregates, each of which contains an approximately uniform size of primary particles. Analysis of the measured size distributions indicates the potential for significant deviation of radiative properties from those associated with the Rayleigh small particle assumption. For very large aggregates, scattering can comprise up to 17% of the Planck-mean extinction at a temperature of 1600 K, and up to 36% of the extinction at a wavelength of 632 nm. Overall, the trends in the data are consistent with the formation of soot on the fuel-rich side of the flame sheet and subsequent agglomeration upon local flame interface extinction.

A COMBINED NARROW- AND WIDE-BAND MODEL FOR COMPUTING THE SPECTRAL ABSORPTION COEFFICIENT OF CO2, CO, H2O, CH4, C2H2, AND NO

Abstract This paper presents a new computational procedure for computing the spectral absorption coefficient of CO 2 , CO, H 2 O, CH 4 , C 2 H 2 , and NO. The procedure is based on a combined narrow- and wide-band model which gives the absorption coefficient as a function of radiation wavelength, temperature, total pressure and partial pressure of the gases. The average line spacing is the only correlation parameter that is adjusted to fit integrated band absorptance data. Results show that the accuracy of the present procedure is comparable to those obtained from using existing correlations. A positive feature of the present procedure is, however, a single model that is applicable to all the gases considered.