Rayleigh scattering measurements of several fluorocarbon gases

Summary The effectiveness of phosphorus‐containing compounds as gas‐phase combustion inhibitors varies widely with flame type. To understand this behavior, experiments are performed with dimethyl methylphosphonate (DMMP) added to the oxidizer stream of methane–air co‐flow diffusion flames (cup‐burner configuration). At low volume fraction, phosphorus (via DMMP addition) is shown to be about four times as effective as bromine (via Br2 addition) at reducing the amount of CO2 required for extinguishment; however, above about 3000 μL/L to 6000 μL/L, the marginal effectiveness of DMMP is approximately zero. In contrast, the diminished effectiveness does not occur for Br2 addition. To explore the role of condensation of active phosphorus‐containing compounds to the particles, laser‐scattering measurements are performed. Finally, to examine the behavior of the flame stabilization region (which is responsible for extinguishment), premixed burning velocity simulations with detailed kinetics are performed for DMMP addition to methane–air flames. Analyses of the numerical results are performed to understand the variation in the inhibition mechanism with temperature, agent loading, and stoichiometry, to interpret the loss of effectiveness for DMMP in the present experiments. Copyright © 2015 John Wiley & Sons, Ltd.

show abstract

“…Experimentally measured Rayleigh cross sections versus literature values for air, CH 4 , CO 2 , and C 3 H 8 ; C 2 HF 5 and He .…”

Section: Methodsmentioning

confidence: 99%

“…Flame shapes and colors are also documented by taking photographs with a DSLR camera (Kodak professional DCS 620) equipped with a Nikkor lens (AF 28/2.8D). [43]; C 2 HF 5 [44] and He [45]. An uncertainty analysis was performed, consisting of calculation of individual uncertainty components and their root mean square summation.…”

Section: Optical Systemmentioning

confidence: 99%

Experimental and numerical investigation of the gas‐phase effectiveness of phosphorus compounds

et al. 2015

View full text Add to dashboard Cite

show abstract

“…Measurements of aerosol scattering, extinction, and absorption coefficients (b scat , b ext , b abs ; Mm −1 ) were carried out using the aerosol albedometer as described in previous literature (Thompson et al, 2008;Dial et al, 2010;Redmond et al, 2011;Ma et al, 2012). Scattering calibration occurred against R-134a (Zadoo and Thompson, 2011) This encourages a conservative estimate of MAC increase at high RH.…”

Section: Measurementsmentioning

confidence: 99%

Atmospheric black carbon can exhibit enhanced light absorption at high relative humidity

Wei

Zhang

Thompson

2013

Preprint

View full text Add to dashboard Cite

<p><strong>Abstract.</strong> Some estimates suggest atmospheric soot (a.k.a. black carbon, BC) warms Earth's climate by roughly 50% the magnitude of increased carbon dioxide. However, one uncertainty in the climate-forcing estimate for BC is the degree to which sunlight absorption is influenced by particle mixing state. Here we show that hygroscopic growth of atmospheric aerosol particles sampled at Houston, TX leads to an enhancement in both light scattering and absorption. Measurements suggest light absorption increases roughly three-four fold at high ambient humidity for coated soot particles. However, when the fraction of coated BC particles was reduced, the absorption enhancement was also reduced, suggesting coatings are crucial for the effect to occur. In addition, the extent to which MAC was increased at high humidity varied considerably over time, even for BC that consistently presented as being coated. This suggests the chemical composition of the coating and/or source of BC may also be an important parameter to constrain MAC enhancement at high humidity. Nonetheless, the results are largely consistent with previous laboratory and model results predicting absorption enhancement. We conclude that the enhanced absorption increases the warming effect of soot aerosol aloft, and global climate models should include parameterizations for RH effects to accurately describe absorptive heating by BC.</p>

show abstract

“…0.9 atm. Instrument calibration was accomplished using filtered air and either SF 6 or R-134a, gases with Rayleigh multipliers of 6.60 and 7.25 times that of air, respectively [23,24]. Figure 2 shows the Mie model correction factors (C) as a function of particle size parameter (α) for particles with differing refractive indices assuming the homogeneous fill case illustrated in Figure 1(b).…”

Section: Experimental Measurement Of Optical Parametersmentioning

confidence: 99%

Modeling and measurements of angular truncation for an aerosol albedometer

Qian¹,

Ma²,

Thompson³

2012

J. Eur. Opt. Soc.-Rapid Publ.

View full text Add to dashboard Cite

In this work, we examine the angular truncation behavior and present correction factors for the aerosol albedometer previously developed in our laboratory. This new instrument makes simultaneous measurement of extinction and scattering coefficients (b ext and b scat) on dispersed aerosol samples. The aerosol extinction coefficient is measured with cavity ring-down spectroscopy (CRDS), and the scattering coefficient is determined through the integrating sphere nephelometer. However, all nephelometers are not able to collect light scattered from an aerosol sample very near the forward (0˚) and reverse (180˚) directions, due to the geometrical constraints. This can result in systematic underestimation of scattering coefficient known as truncation error. In order to account for this problem and describe scattering by aerosols more precisely, correction factors (C) for this angular non-ideality have been theoretically developed. Truncation angles (θ) were calculated upon consideration of the geometry of the sphere nephelometer. As truncation error largely depends on particle size and refractive index, C values were computed for a series of spherical, homogeneous aerosol particles with different known particle sizes and refractive indices by Lorenz-Mie theory. Measurements on size-selected, laboratory generated aerosols of known size and composition allowed empirical measurement of truncation correction factors to compare with the Mie model results. Results indicate the model we built overestimates the fraction of light not collected by the sphere. Empirically observed correction factors of ≤ 1.12 for particles with size parameters (α) < 6 were determined. In addition, the effect of number of particles within the probe beam on the suitability of correction factors was also examined. Observations support the hypothesis that particles are rapidly transported / mixed through the probe beam, and measurement integration times as short as 52 s yield data that is indistinguishable from the probe region being homogeneously filled with aerosol, even at very low particle concentrations.

show abstract

Rayleigh scattering measurements of several fluorocarbon gases

Cited by 5 publications

References 9 publications

Experimental and numerical investigation of the gas‐phase effectiveness of phosphorus compounds

Experimental and numerical investigation of the gas‐phase effectiveness of phosphorus compounds

Atmospheric black carbon can exhibit enhanced light absorption at high relative humidity

Modeling and measurements of angular truncation for an aerosol albedometer

Contact Info

Product

Resources

About