Effects of oxygen depletion on soot production, emission and radiative heat transfer in opposed-flow flame spreading over insulated wire in microgravity

This paper investigates experimentally and numerically pressure effects on soot production and radiative heat transfer in non-buoyant opposed-flow flames spreading over wires coated by Low Density PolyEthylene (LPDE). Experiments, conducted in parabolic flights, consider pressure levels ranging from 50.7 kPa to 121.6 kPa and an oxidizer flowing parallel to the wire's axis at a velocity of 150 mm/s and composed of 20% O2/80% N2 in volume. The numerical model includes a detailed chemistry, a two-equation smoke-point based soot production model, a radiation model coupling the Full-Spectrum correlated-k method with the finite volume method and a simple degradation model for LDPE. An analysis of the experimental data shows that the spread rate, the pyrolysis mass flow rate, and the residence time for soot formation are independent of pressure whereas the soot formation rate is third-order in pressure. The model reproduces quantitatively the effects of pressure on soot production and captures the transition from non-smoking to smoking flames. The radiant fraction increases with pressure because of an enhancement in soot radiation whereas the contribution of radiating gases remains approximately constant over the range of pressures considered. In addition, gas radiation dominates at pressure lower than 75 kPa whereas soot radiation prevails at higher-pressure levels. Consistently with the data obtained at normal gravity, the smoke-point transition is found to occur for a radiant fraction of about 0.3 and the soot oxidation freezing temperature is estimated in the range 1350-1450K. Eventually, whatever the pressure considered, the surface re-radiation from the wire is higher than the incident radiative flux from the flame to the surface along the entire wire. This shows that radiative heat transfer contributes negatively to the heating of the unburnt LDPE and to the heat balance along the pyrolysing surface

Refractory chronic ankle pain controlled with pulsed radiofrequency: case report

JUSTIFICATIVA E OBJETIVOS: A radiofrequência (RF) é uma corrente alternada com frequência de oscilação de 500.000 Hz, que tem sido usada com sucesso no tratamento de algumas morbidades que cursam com dor crônica. O objetivo deste relato de caso foi mostrar o uso bem sucedido da RF pulsátil do nervo sural para o tratamento de dor crônica no tornozelo. RELATO DO CASO: Paciente do sexo feminino, 60 anos, que há 5 anos apresentava dor em tornozelo direito, refratária ao tratamento com opioides, anti-inflamatório não esteroides (AINES), dipirona, antidepressivos e anticonvulsivantes, fisioterapia, infiltrações localizadas, acupuntura e palmilha. A paciente foi submetida a aplicação de RF pulsátil de nervo sural direito. O local da inserção da agulha foi na linha entre o tendão de Aquiles e maléolo lateral, região inicial de tendão de Aquiles e final dos músculos sóleo e gastrocnêmio. A estimulação sensitiva para identificação do nervo sural foi com 0,5 volts e 50 Hz. A corrente pulsátil foi aplicada durante 140 segundos com 45 volts com temperatura de até 42º C. Foram realizadas duas aplicações, ocorrendo melhora de cerca de 80% da dor, permitindo que a paciente pudesse deambular ou permanecer em pé, sem maiores dificuldades. CONCLUSÃO: A RF pulsátil do nervo sural pode ser uma opção para o controle das dores crônicas em tornozelo

Accessing the soot-related radiative heat feedback in a flame spreading in microgravity: optical designs and associated limitations

Novel, high-fidelity results related to soot from microgravity flames were obtained by an international topical team on fire safety in space. More specifically, embedded optical techniques for evaluation of the soot-related radiative feedback to the base material from a spreading non-premixed flame in microgravity were developed. The configuration used a non-buoyant axisymmetric flame propagating in an opposed laminar stream overa Low Density PolyEthylene coating of an electrical wire. Within this context, both the standard Broadband Two Color Pyrometry (B2CP) and its recent extension Broadband Modulated Absorption/Emission (BMAE) technique can be deployed to measure the spatial distribution of soot temperature and volume fraction within the flame. Both fields are then processed to establish the field of local radiative balance attributed to soot within the flame, and ultimately the soot contribution to the radiative flux to the wire. The present study first assesses the consistency of the methodology contrasting an experimental frame and a synthetic one, the latter being produced by a signal modeling that processes fields delivered by a numerical simulation of the configuration as inputs. Using the synthetic signals obtained, the fields of local radiative balance within the flame are then computed and significant discrepancies were disclosed locally between the fields originating from the synthetic BMAE and B2CP inputs. Nevertheless, the subsequent evaluation of the soot-related radiative heat feedback to the wire shows that a weak deviation among the techniques implemented is expected. This finding is corroborated by similar evaluations conducted with experimental BMAE and B2CP measurements obtained in parabolic flights. As BMAE is implemented in an ISS configuration within the SCEM rig, BMAE and B2CP will soon provide long-duration soot observations in microgravity. In order to contrast the upcoming results, this current study quantifies discrepancies originating from the post-processing regarding soot temperature and volume fraction, and shows that the radiative feedback evaluation from both methods should be consistent

Influence of turbulence-radiation interactions in laboratory-scale methane pool fires

International audienceElsevier The objective of this study is to assess the effects of Turbulence Radiation Interactions (TRI) on the structure of small-scale pool fires and on the radiative fluxes transferred to surrounding surfaces. Fire-induced flow is modeled by using a buoyancy-modified k-epsilon model and the Steady Laminar Flamelet (SLF) model coupled with a presumed Probability Density Function (pdf) approach. A 34-kW methane pool fire produced by burner with a diameter of 0.38 m is simulated by neglecting radiation, by considering radiation without TRIs, and by considering radiation with TRIs. Computations carried out with radiation are based on the Full Spectrum Correlated-k (FSCK) method. TRIs are taken into account by considering the Optically-Thin Fluctuation Approximation (OTFA). The mean radiative source term and the mean RTE are then closed by using a presumed pdf of the mixture fraction, scalar dissipation rate, and enthalpy defect. When TRIs are considered predicted flame structure, radiant fraction and radiative fluxes are found in quantitative agreement with the available experimental data. Simulations reveal that TRIs significantly enhance radiative losses and substantially contribute to the drop in temperature due to radiation. TRIs also contribute to reduce turbulence levels and the root mean square (rms) values of temperature fluctuations. In addition radiative heat fluxes on remote targets are found to be considerably higher than those obtained from radiative calculations based on mean properties. Finally different levels of closure for the TRI-related terms are assessed. Model results show that the complete absorption coefficient-Planck function correlation should be considered in order to properly take into account the influence of TRIs on the emission term whereas the effect of absorption coefficient self-correlation on the absorption term is a reduction by about 12% of the radiant fraction. (C) 2012 Elsevier Masson SAS. All rights reserved

RADIATIVE HEAT TRANSFER THROUGH THE FUEL-RICH CORE OF LABORATORY-SCALE POOL FIRES

8th Mediterranean Combustion Symposium, Izmir, TURKEY, SEP 08-13, 2013International audienceRadiative heat transfer calculations are conducted along the axis of six axisymmetric pool fires by using the exact line-by-line (LBL) method, the narrow band correlated k (NBCK) model, the full-spectrum correlated k (FSCK) model, the multi-scale full-spectrum k-distribution (MSFSK) model, and the wide-band model implemented in the fire dynamic simulator (FDS). The two baseline cases correspond to 34 kW and 176 kW methane pool fires generated on a burner of 0.38 m diameter. For each heat release rate, two other moderately and heavily sooting pool fires were generated by considering higher soot volume fractions while keeping temperature and gaseous species concentrations unaltered. For each radiative model, the corresponding absorption coefficients for carbon dioxide, water vapor, carbon monoxide, and methane were generated from the same high-resolution spectroscopic databases. Model results show that the contribution of carbon monoxide to the radiative intensity can be neglected, whereas that of methane increases with the heat release rate (HRR) and decreases as the soot loading increases. It is also found that the gray approximation for soot holds for the 34 kW pool fires and the weakly and moderately sooting 176 kW pool fires but ceases to be valid for the heavily sooting 176 kW pool fire. Concerning the accuracy of the different approximate radiative models, comparisons with the LBL solutions show that the NBCK model can be used as a reference if LBL solutions are not available. On the other hand, the FDS wide-band model fails in predicting accurately the radiative intensity through the fuel-rich core of pool fires. Finally, the FSCK provide predictions within 10% of LBL solutions with the exception of the heavily sooting 176 kW pool fire where the strong attenuation of radiation by methane invalidates the correlated assumption of the absorption coefficient. In this case, the MSFSK model must be considered, improving substantially the predictions of the FSCK

Experimental study of the burning rate of small-scale forest fuel layers

International audienceAn experimental study of the burning rates of small-scale forest fuel layers composed of maritime pine needles is carried out by using the FM-Global Fire Propagation Apparatus (FPA). Three fuel loads, corresponding to fuel volume fractions of about 0.02, 0.04 and 0.08, are exposed to external heat fluxes in the range 15-30 kW/m(2). The analysis of the experimental data focuses on the flaming stage. The time evolution of the mass loss rate exhibits the same trend no matter the external radiant heat flux and the fuel load considered. Just after ignition (short time) a linear increase is observed whereas after the peak (long time) the degradation process can be described by a first order Arrhenius law. The flaming residence times and the characteristic chemical time scale for the long time process are found to be weakly influenced by the external radiant heat flux while they increase exponentially with the fuel load. In addition, an analysis of the remaining mass of solid fuel at flame extinction shows that the char oxidation process becomes increasingly important as the fuel volume fraction becomes larger. Finally flame heights, determined from CH* measurements, are found to be consistent with those predicted by the classical correlations of the literature. (C) 2013 Elsevier Masson SAS. All rights reserved