Predicting the ignition of crown fuels above a spreading surface fire. Part II: model evaluation

2006 ◽  
Vol 15 (1) ◽  
pp. 61 ◽  
Author(s):  
Miguel G. Cruz ◽  
Bret W. Butler ◽  
Martin E. Alexander
Keyword(s):  
Particle Surface ◽  
Lower Boundary ◽  
Ground Surface ◽  
Volume Ratio ◽  
Fuel Particle ◽  
Particle Surface Area ◽  
Surface Fire ◽  
Fuel Layer ◽  
Model Predictions ◽  
A Minor

A crown fuel ignition model (CFIM) describing the temperature rise and subsequent ignition of the lower portion of tree crowns above a spreading surface fire was evaluated through a sensitivity analysis, comparison against other models, and testing against experimental fire data. Results indicate that the primary factors influencing crown fuel ignition are those determining the depth of the surface fire burning zone and the vertical distance between the ground/surface fuel strata and the lower boundary of the crown fuel layer. Intrinsic crown fuel properties such as fuel particle surface area-to-volume ratio and foliar moisture content were found to have a minor influence on the process of crown fuel ignition. Comparison of model predictions against data collected in high-intensity experimental fires and predictions from other models gave encouraging results relative to the validity of the model system.

Heterogeneous formation of HONO and its impacts on haze formation in the YRD region of China

2020 ◽  
Author(s):  
Jun Zheng ◽  
Xiaowen Shi ◽  
Yan Ma
Keyword(s):  
Heterogeneous Reaction ◽  
Particle Surface ◽  
Ground Surface ◽  
Yangtze River Delta ◽  
Heterogeneous Reactions ◽  
Atmospheric Oxidation ◽  
Industrial Zone ◽  
Particle Surface Area ◽  
Oxidation Capacity ◽  
The Yrd

<p>A suite of instruments were deployed to simultaneously measure nitrous acid (HONO), nitrogen oxides (NO<sub>x</sub>= NO + NO<sub>2</sub>), carbon monoxide (CO), ozone (O<sub>3</sub>), volatile organic compounds (VOCs, including formaldehyde (HCHO)) and meteorological parameters near a typical industrial zone in Nanjing of the Yangtze River Delta region, China. High levels of HONO were detected using a wet chemistry-based method. HONO ranged from 0.03-7.04 ppbv with an average of 1.32 ±0.92 ppbv. Elevated daytime HONO was frequently observed with a minimum of several hundreds of pptv on average, which cannot be explained by the homogeneous OH + NO reaction (P<sub>OH+NO</sub>) alone, especially during periods with high loadings of particulate matters (PM<sub>2.5</sub>). The HONO chemistry and its impact on atmospheric oxidation capacity in the study area were further investigated using a MCM-box model. The results show that the average hydroxyl radical (OH) production rate was dominated by the photolysis of HONO (7.13×10<sup>6</sup>molecules cm<sup>-3 </sup>s<sup>-1</sup>), followed by ozonolysis of alkenes (3.94×10<sup>6</sup>molecules cm<sup>-3 </sup>s<sup>-1</sup>), photolysis of O<sub>3</sub>(2.46×10<sup>6</sup>molecules cm<sup>-3 </sup>s<sup>-1</sup>) and photolysis of HCHO (1.60×10<sup>6</sup>molecules cm<sup>-3 </sup>s<sup>-1</sup>), especially within the plumes originated from the industrial zone. The observed similarity between HONO/NO<sub>2</sub>and HONO in diurnal profiles strongly suggests that HONO in the study area was likely originated from NO<sub>2</sub>heterogeneous reactions. The averagenighttimeNO<sub>2</sub>to HONO conversion ratewas determined to be ~0.9% hr<sup>-1</sup>. Good correlation between nocturnal HONO/NO<sub>2</sub>and the products of particle surface area density (S/V) and relative humidity (RH), S/V×RH,supports the heterogeneous NO<sub>2</sub>/H<sub>2</sub>O reaction mechanism. The other HONO source, designated as P<sub>unknonwn</sub>, was about twice as much as P<sub>OH+NO </sub>on average and displayed a diurnal profile with an evidently photo-enhanced feature, i.e., photosensitized reactions of NO<sub>2</sub>may be an important daytime HONO source. Nevertheless, our results suggest that daytime HONO formation was mostly due to the light-induced conversion of NO<sub>2</sub>on aerosol surfaces but heterogeneous NO<sub>2</sub>reactions on ground surface dominated nocturnal HONO production. Concurred elevated HONO and PM<sub>2.5</sub>levels strongly indicate that high HONO may increase the atmospheric oxidation capacity and further promote the formation of secondary aerosols, which may in turn synergistically boost NO<sub>2</sub>/HONO conversion by providing more heterogeneous reaction sites.</p>

Improvement of monitoring of tertiary filtration with particle counting

2006 ◽  
Vol 6 (1) ◽  
pp. 1-9
Author(s):  
V. Miska ◽  
J.H.J.M. van der Graaf ◽  
J. de Koning
Keyword(s):  
Particle Surface ◽  
Minor Effect ◽  
Particle Size Distributions ◽  
Particle Volume ◽  
Mass Distributions ◽  
Particle Counting ◽  
Total Particle ◽  
Particle Counts ◽  
A Minor ◽  
Sample Dilution

Nowadays filtration processes are still monitored with conventional analyses like turbidity measurements and, in case of flocculation–filtration, with phosphorus analyses. Turbidity measurements have the disadvantage that breakthrough of small flocs cannot be displayed, because of the blindness regarding changes in the mass distributions. Additional particle volume distributions calculated from particle size distributions (PSDs) would provide a better assessment of filtration performance. Lab-scale experiments have been executed on a flocculation–filtration column fed with effluent from WWTP Beverwijk in The Netherlands. Besides particle counting at various sampling points, the effect of sample dilution on the accuracy of PSD measurements has been reflected. It was found that the dilution has a minor effect on PSD of low turbidity samples such as process filtrate. The correlation between total particle counts, total particle volume (TPV) and total particle surface is not high but is at least better for diluted measurements of particles in the range 2–10 μm. Furthermore, possible relations between floc-bound phosphorus and TPV removal had been investigated. A good correlation coefficient is found for TPV removal versus floc-bound phosphorus removal for the experiments with polyaluminiumchloride and the experiments with single denitrifying and blank filtration.

Quantities Directly Measurable by Scattering

2018 ◽  
Author(s):  
Eaton E. Lattman ◽  
Thomas D. Grant ◽  
Edward H. Snell
Keyword(s):  
Molecular Weight ◽  
Particle Shape ◽  
Particle Surface ◽  
Scattering Data ◽  
Radius Of Gyration ◽  
Particle Volume ◽  
Particle Surface Area ◽  
Scattering Angle ◽  
Particle Dimension ◽  
Maximum Particle

In this chapter we note that solution scattering data can be divided into four regions. At zero scattering angle, the scattering provides information on molecular weight of the particle in solution. Beyond that, the scattering is influenced by the radius of gyration. As the scattering angle increases, the scattering is influenced by the particle shape, and finally by the interface with the particle and the solution. There are a number of important invariants that can be calculated directly from the data including molecular mass, radius of gyration, Porod invariant, particle volume, maximum particle dimension, particle surface area, correlation length, and volume of correlation. The meaning of these is described in turn along with their mathematical derivations.

Influence of particle surface area on the toxicity of insoluble manganese dioxide dusts

1997 ◽  
Vol 71 (12) ◽  
pp. 725-729 ◽  
Author(s):  
Dominique Lison ◽  
Cécile Lardot ◽  
François Huaux ◽  
Giovanna Zanetti ◽  
Bice Fubini
Keyword(s):  
Manganese Dioxide ◽  
Surface Area ◽  
Particle Surface ◽  
Particle Surface Area

scholarly journals Ice nucleation abilities of soot particles determined with the Horizontal Ice Nucleation Chamber

2018 ◽  
Vol 18 (18) ◽  
pp. 13363-13392 ◽  
Author(s):  
Fabian Mahrt ◽  
Claudia Marcolli ◽  
Robert O. David ◽  
Philippe Grönquist ◽  
Eszter J. Barthazy Meier ◽  
...  
Keyword(s):  
Particle Size ◽  
Water Saturation ◽  
Particle Surface ◽  
Water Vapor Sorption ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Particle Surface Area ◽  
Soot Particles ◽  
Microphysical Properties ◽  
Homogeneous Freezing

Abstract. Ice nucleation by different types of soot particles is systematically investigated over the temperature range from 218 to 253 K relevant for both mixed-phase (MPCs) and cirrus clouds. Soot types were selected to represent a range of physicochemical properties associated with combustion particles. Their ice nucleation ability was determined as a function of particle size using relative humidity (RH) scans in the Horizontal Ice Nucleation Chamber (HINC). We complement our ice nucleation results by a suite of particle characterization measurements, including determination of particle surface area, fractal dimension, temperature-dependent mass loss (ML), water vapor sorption and inferred porosity measurements. Independent of particle size, all soot types reveal absence of ice nucleation below and at water saturation in the MPC regime (T>235 K). In the cirrus regime (T≤235 K), soot types show different freezing behavior depending on particle size and soot type, but the freezing is closely linked to the soot particle properties. Specifically, our results suggest that if soot aggregates contain mesopores (pore diameters of 2–50 nm) and have sufficiently low water–soot contact angles, they show ice nucleation activity and can contribute to ice formation in the cirrus regime at RH well below homogeneous freezing of solution droplets. We attribute the observed ice nucleation to a pore condensation and freezing (PCF) mechanism. Nevertheless, soot particles without cavities of the right size and/or too-high contact angles nucleate ice only at or well above the RH required for homogeneous freezing conditions of solution droplets. Thus, our results imply that soot particles able to nucleate ice via PCF could impact the microphysical properties of ice clouds.

scholarly journals Effect of Home Grinding on Properties of Brewed Coffee

2014 ◽  
Vol 4 (1) ◽  
pp. 77
Author(s):  
Christopher Murray ◽  
Thamara Laredo
Keyword(s):  
Particle Size ◽  
Fourier Transform ◽  
Distribution Density ◽  
Particle Surface ◽  
Particle Surface Area ◽  
Present Evidence ◽  
Caffeine Content ◽  
General Recommendation ◽  
Grinding Time ◽  
Ground Coffee

<p>We present measurements of particle size distribution, density, loss of coffee on brewing and caffeine content in brewed coffee (as measured using Fourier Transform Infrared Spectroscopy) as a function of grinding time using a blade-type grinder. In general, there is not a lack of correlation between coffee properties and grinding for grinding times in excess of 42 s, but mass loss on brewing and caffeine content are both increased with grinding times between 0 and 42 s. In addition, we present evidence that this dependence of the composition of brewed coffee on grinding time is a function of increased coffee particle surface area that results from grinding, rather than increased loss of grounds into the brewed beverage or increased percolation time. Finally, we present a general recommendation for determining equivalency between small amounts of finely ground coffee and larger amounts of coarser-ground coffee.</p>

scholarly journals Self-Cleaning Limestone Paint Modified by Nanoparticles TiO2 Synthesized from TiCl3 as Precursors and PEG6000 as Dispersant

2017 ◽  
Vol 12 (3) ◽  
pp. 351 ◽  
Author(s):  
Nur Fadhilah ◽  
Niki Etruly ◽  
Maktum Muharja ◽  
Dyah Sawitri
Keyword(s):  
Particle Surface ◽  
Wall Painting ◽  
Reaction Engineering ◽  
Mass Ratio ◽  
Particle Surface Area ◽  
Surface Tension Reduction ◽  
Agglomeration Process ◽  
Activating Agent ◽  
Self Cleaning ◽  
Average Size

Limestone is commonly used for wall painting, but it is easy to be dirty. In this study, a self-cleaning limestone paint was synthesized by modifying dispersant and TiO2 nanoparticles. The TiO2 that prepared by TiCl3 were functionalized with PEG6000 as a surface activating agent. The paint achieved highest impurity degradation of 83.11 % for the mass ratio of TiO2 and PEG6000 (MRTP) of 1: 6, in which TiO2 average size distribution was 75.81 µm2, the particle surface area of TiO2 was 2,544 µm2, and the smallest contact angle was 7°. It was found that the dispersant (PEG6000) significantly improved the self-cleaning ability of limestone paint. The surface tension reduction from PEG6000-modified prevented the agglomeration process of TiO2 and suggests that the limestone paint a good self-cleaning coating for wall painting. Copyright © 2017 BCREC Group. All rights reservedReceived: 21st November 2016; Revised: 10th September 2017; Accepted: 11st September 2017; Available online: 27th October 2017; Published regularly: December 2017How to Cite: Fadhilah, N., Etruly, N., Muharja, M., Sawitri, D. (2017). Self-Cleaning Limestone Paint Modified by Nanoparticles TiO2 Synthesized from TiCl3 as Precursors and PEG6000 as Dispersant. Bulletin of Chemical Reaction Engineering & Catalysis, 12(3): 351-356 (doi:10.9767/bcrec.12.3.800.351-356) 

scholarly journals Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of <i>α</i>-pinene

2016 ◽  
Vol 16 (10) ◽  
pp. 6495-6509 ◽  
Author(s):  
Karoliina Ignatius ◽  
Thomas B. Kristensen ◽  
Emma Järvinen ◽  
Leonid Nichman ◽  
Claudia Fuchs ◽  
...  
Keyword(s):  
Secondary Organic Aerosol ◽  
Solid Phase ◽  
Particle Surface ◽  
Amorphous Solid ◽  
Organic Aerosol ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Particle Surface Area ◽  
Semi Solid ◽  
Heterogeneous Ice Nucleation

Abstract. There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles. The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 °C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between −39.0 and −37.2 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nucleating particle budget.

Sign in / Sign up

Export Citation Format

Share Document