Lean flammability limit as a fundamental refrigerant property: Phase 3. Final technical report, February 1997--February 1998

Alternative refrigerants are being developed by industry to prevent the further destruction of stratospheric ozone by chlorofluorocarbons (CFCs), which had been the working fluids of choice for many air-conditioning and refrigeration machines. Hydrofluorocarbons (HFCs) are one class of compounds that are being pursued as replacements because their ozone depletion potential is zero. In general, the exchange of fluorine atoms on an HFC molecule with hydrogen atoms decreases its atmospheric lifetime, and it may also increase the efficiency of the working fluid. Both of these effects are highly desirable from environmental considerations since they act to mitigate global warming. Unfortunately, more hydrogen on a HFC is usually associated with an increase in flammability. An accepted method for determining the flammability limits of gaseous fuels is ASTM Standard E 681. The minimum and maximum concentrations of the fuel in air for flame propagation are based upon the observed ignition and growth of a flame in a vessel filled with a quiescent fuel/air mixture. a Clear distinction is sought between a non-propagating flicker and a flame which has enough horizontal propagation to be hazardous. This report reviews the past work done on premixed, counter-flowing flames, describes the current counter-flow burner facility and operating procedures, presents the experimental results with the analysis that yields the above flammability limits, and recommends further activities that could lead to a science-based methodology for assessing the risk of fire from refrigeration machine working fluids. 30 figs

Measurement and Modeling of Particle Radiation in Coal Flames

This work aims at developing a methodology that can provide information of in-flame particle radiation in industrial-scale flames. The method is based on a combination of experimental and modeling work. The experiments have been performed in the high-temperature zone of a 77 kWth swirling lignite flame. Spectral radiation, total radiative intensity, gas temperature, and gas composition were measured, and the radiative intensity in the furnace was modeled with an axisymmetric cylindrical radiation model using Mie theory for the particle properties and a statistical narrow-band model for the gas properties. The in-flame particle radiation was measured with a Fourier transform infrared (FTIR) spectrometer connected to a water-cooled probe via fiber optics. In the cross-section of the flame investigated, the particles were found to be the dominating source of radiation. Apart from giving information about particle radiation and temperature, the methodology can also provide estimates of the amount of soot radiation and the maximum contribution from soot radiation compared to the total particle radiation. In the center position in the flame, the maximum contribution from soot radiation was estimated to be less than 40% of the particle radiation. As a validation of the methodology, the modeled total radiative intensity was compared to the total intensity measured with a narrow angle radiometer and the agreement in the results was good, supporting the validity of the used approach

Mutual Information for the Detection of Crush

Fatal crush conditions occur in crowds with tragic frequency. Event organizers and architects are often criticised for failing to consider the causes and implications of crush, but the reality is that both the prediction and prevention of such conditions offer a significant technical challenge. Full treatment of physical force within crowd simulations is precise but often computationally expensive; the more common method of human interpretation of results is computationally “cheap” but subjective and time-consuming. This paper describes an alternative method for the analysis of crowd behaviour, which uses information theory to measure crowd disorder. We show how this technique may be easily incorporated into an existing simulation framework, and validate it against an historical event. Our results show that this method offers an effective and efficient route towards automatic detection of the onset of crush

Lean flammability limit as a fundamental refrigerant property: Phase 2. Interim technical report, 1 April 1995--30 March 1996

The flammability of alternative, non-ozone depleting refrigerants is an issue of growing importance to the air-conditioning and refrigeration industry. Test methods developed decades ago are being stretched to their limits when measuring the combustion behavior of weakly flammable refrigerants. This work is Phase 2 of a three part project to determine the feasibility, accuracy, and applicability of a premixed opposed-flow burner as an alternative means of measuring lean flammability limits. In this work, the Phase 2 burner demonstrates the precision available to the opposed-flow technique for evaluating the lean flammability limit of weak fuels. Using opposed, converging nozzles, two jets support a premixed twin flame at different global strain rates and permit evaluation of the corresponding fuel concentration at the extinction point. Comparisons with published data support that the LFL{sub 0}, a lean flammability limit value defined by the extrapolation of the extinction conditions to zero global strain, yields a consistent value. Using a computer simulation to analyze the uncertainty, the lean flammability limit of refrigerants in dry air is found. Concurrent computational modeling of the combustion of refrigerants in air, individually and in mixtures has been performed with the chemical kinetics code CHEMKIN. Estimates of the impact of the initial conditions (equivalence ratio, fuel composition, temperature, and relative humidity) on the magnitude of the laminar flame speed of a zero strain flame are made

Survey of Fire Detection Technologies and System Evaluation/Certification Methodologies and Their Suitability for Aircraft Cargo Compartments

As part of the National Aeronautics and Space Administration (NASA) initiated program on global civil aviation, NIST is assisting Federal Aviation Administration in its research to improve fire detection in aircraft cargo compartments. Aircraft cargo compartment detection certification methods have been reviewed. The Fire Emulator-Detector Evaluator (FE/DE) has been designed to evaluate fire detection technologies such as new sensors, multi-element detectors, and detectors that employ complex algorithms. The FE/DE is a flow tunnel that can reproduce velocity, temperature, smoke, and Combustion gas levels to which a detector might be exposed during a fire. A scientific literature survey and patent search have been conducted relating to existing and emerging fire detection technologies, and the potential use of new fire detection strategies in cargo compartment areas has been assessed. In the near term, improved detector signal processing and multi-sensor detectors based on combinations of smoke measurements, combustion gases and temperature are envisioned as significantly impacting detector system performance