6 research outputs found
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Characterization of soot properties in two-meter JP-8 pool fires.
The thermal hazard posed by large hydrocarbon fires is dominated by the radiative emission from high temperature soot. Since the optical properties of soot, especially in the infrared region of the electromagnetic spectrum, as well as its morphological properties, are not well known, efforts are underway to characterize these properties. Measurements of these soot properties in large fires are important for heat transfer calculations, for interpretation of laser-based diagnostics, and for developing soot property models for fire field models. This research uses extractive measurement diagnostics to characterize soot optical properties, morphology, and composition in 2 m pool fires. For measurement of the extinction coefficient, soot extracted from the flame zone is transported to a transmission cell where measurements are made using both visible and infrared lasers. Soot morphological properties are obtained by analysis via transmission electron microscopy of soot samples obtained thermophoretically within the flame zone, in the overfire region, and in the transmission cell. Soot composition, including carbon-to-hydrogen ratio and polycyclic aromatic hydrocarbon concentration, is obtained by analysis of soot collected on filters. Average dimensionless extinction coefficients of 8.4 {+-} 1.2 at 635 nm and 8.7 {+-} 1.1 at 1310 nm agree well with recent measurements in the overfire region of JP-8 and other fuels in lab-scale burners and fires. Average soot primary particle diameters, radius of gyration, and fractal dimensions agree with these recent studies. Rayleigh-Debye-Gans theory of scattering applied to the measured fractal parameters shows qualitative agreement with the trends in measured dimensionless extinction coefficients. Results of the density and chemistry are detailed in the report
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Soot formation, transport, and radiation in unsteady diffusion flames : LDRD final report.
Fires pose the dominant risk to the safety and security of nuclear weapons, nuclear transport containers, and DOE and DoD facilities. The thermal hazard from these fires primarily results from radiant emission from high-temperature flame soot. Therefore, it is necessary to understand the local transport and chemical phenomena that determine the distributions of soot concentration, optical properties, and temperature in order to develop and validate constitutive models for large-scale, high-fidelity fire simulations. This report summarizes the findings of a Laboratory Directed Research and Development (LDRD) project devoted to obtaining the critical experimental information needed to develop such constitutive models. A combination of laser diagnostics and extractive measurement techniques have been employed in both steady and pulsed laminar diffusion flames of methane, ethylene, and JP-8 surrogate burning in air. For methane and ethylene, both slot and coannular flame geometries were investigated, as well as normal and inverse diffusion flame geometries. For the JP-8 surrogate, coannular normal diffusion flames were investigated. Soot concentrations, polycyclic aromatic hydrocarbon (PAH) laser-induced fluorescence (LIF) signals, hydroxyl radical (OH) LIF, acetylene and water vapor concentrations, soot zone temperatures, and the velocity field were all successfully measured in both steady and unsteady versions of these various flames. In addition, measurements were made of the soot microstructure, soot dimensionless extinction coefficient (&), and the local radiant heat flux. Taken together, these measurements comprise a unique, extensive database for future development and validation of models of soot formation, transport, and radiation
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Closed-loop biomass co-firing in a laboratory reactor and in a full-scale boiler.
Co-firing tests were conducted in a pilot-scale reactor at Sandia National Laboratories and in a boiler at the Hawaiian Commercial & Sugar factory at Puunene, Hawaii. Combustion tests were performed in the Sandia Multi-Fuel Combustor using Australian coal, whole fiber cane including tops and leaves processed at three different levels (milled only, milled and leached, and milled followed by leaching and subsequent milling), and fiber cane stripped of its tops and leaves and heavily processed through subsequent milling, leaching, and milling cycles. Testing was performed for pure fuels and for biomass co-firing with the coal at levels of 30% and 70% by mass. The laboratory tests revealed the following information: (1) The biomass fuels convert their native nitrogen into NO more efficiently than coal because of higher volatile content and more reactive nitrogen complexes. (2) Adding coal to whole fiber cane to reduce its tendency to form deposits should not adversely affect NO emissions. ( 3 ) Stripped cane does not offer a NO advantage over whole cane when co-fired with coal. During the field test, Sandia measured 0 2 , C02, CO, SO2, and NO concentrations in the stack and gas velocities near the superheater. Gas concentrations and velocities fluctuated more during biomass co-firing than during coal combustion. The mean 0 2 concentration was lower and the mean C02 concentration was higher during biomass co-firing than during coal combustion. When normalized to a constant exhaust 0 2 concentration, mean CO concentration was higher and mean NO concentration was lower for biomass co-firing than for coal. The SO2 concentration tracked the use of Bunker C fuel oil. When normalized by the amount of boiler energy input, the amounts of NO and SO2 formed were lower during biomass co-firing than during coal combustion. The difference between NOx trends in the lab and in the field are most likely a result of less effective heat and mass transfer in the boiler. Particles were sampled near the superheater tube using an impaction probe and were analyzed using scanning electron microscopy. Particle loading appeared higher for biomass co-firing than for coal combustion, especially for the smaller particle diameters. Laser-induced breakdown spectroscopy (LIBS) was used to detect silicon, aluminum, titanium, iron, calcium, magnesium, sodium, and potassium concentrations near the superheater. LIBS provided an abundant amount of real-time information. The major constituents of the fuel ash (silicon and aluminum) were also the major measured inorganic constituents of the combustion products. The combustion products were enriched in sodium relative to the fuel ash during all tests, and they were enriched in potassium for the biomass co-firing tests. Alkali metals are enriched because compounds containing these elements are more readily releasable into the combustion products than refractory components that remain in large particles such as silicon, aluminum, and titanium. Relative to the measured deposit chemistry, the combustion flows were enriched in iron, sodium, and potassium, constituents that are known to form fumes laden with fine particles and/or vapors. The LIBS results yield insight into the deposition mechanism: Impaction of larger particles dominates over fume deposition. The present application of LIBS reveals its potential to provide real-time field information on the deposition propensity of different fuels and the effects of different fuels and boiler operating conditions
Risk of COVID-19 after natural infection or vaccinationResearch in context
Summary: Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health
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Risk of COVID-19 after natural infection or vaccinationResearch in context
Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health