On the flame length in firewhirls with strong vorticity

AbstractApproximately one billion people across the globe are living in informal settlements with a large potential fire risk. Due to the high dwelling density, a single informal settlement dwelling fire may result in a very serious fire disaster leaving thousands of people homeless. In this work, a simple physics-based theoretical model was employed to assess the critical fire separation distance between dwellings. The heat flux and ejected flame length were obtained from a full-scale dwelling tests with ISO 9705 dimension (3.6 m × 2.4 m × 2.4 m) to estimate the radiation decay coefficient of the radiation heat flux away from the open door. The ignition potential of combustible materials in adjacent dwellings are analyzed based on the critical heat flux from cone calorimeter tests. To verify the critical distance in real informal settlement fire, a parallel method using aerial photography within geographic information systems (GIS), was employed to determine the critical separation distances in four real informal settlement fires of 2014–2015 in Masiphumelele, Cape Town, South Africa. The fire-spread distances were obtained as well through the real fires. The probabilistic analysis was conducted by Weibull distribution and logistic regression, and the corresponding separation distances were given with different fire spread probabilities. From the experiments with the assumption of no interventions and open doors and windows, it was established that the heat flux would decay from around 36 kW/m2 within a distance of 1.0 m to a value smaller than 5 kW/m2 at a distance of 4.0 m. Both experiments and GIS results agree well and suggest the ignition probabilities at distances of 1.0 m, 2.0 m and 3.0 m are 97%, 52% and 5% respectively. While wind is not explicitly considered in the work, it is implicit within the GIS analyses of fire spread risk, therefore, it is reasonable to say that there is a relatively low fire spread risk at distances greater than 3 m. The distance of 1.0 m in GIS is verified to well and conservatively predict the fire spread risk in the informal settlements.

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Effects of Air Temperature on Combustion Characteristics of LPG Diffusion Flame

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1008.128 ◽

2020 ◽

Vol 1008 ◽

pp. 128-138

Author(s):

Ahmed M. Salman ◽

Ibrahim A. Ibrahim ◽

Hamada M. Gad ◽

Tharwat M. Farag

Keyword(s):

Air Temperature ◽

Diffusion Flame ◽

Nitrogen Addition ◽

Flame Length ◽

Combustion Characteristics ◽

Operating Conditions ◽

Low Oxygen ◽

Air Temperatures ◽

Air Stream ◽

Wide Range

In the present study, the combustion characteristics of LPG gaseous fuel diffusion flame at elevated air temperatures were experimentally investigated. An experimental test rig was manufactured to examine a wide range of operating conditions. The investigated parameters are the air temperatures of 300, 350, 400, 450, and 500 K with constant percentage of nitrogen addition in combustion air stream of 5 % to give low oxygen concentration of 18.3 % by mass at constant air swirl number, air to fuel mass ratio, and thermal load of 1.5, 30, and 23 kW, respectively. The gaseous combustion characteristics were represented as axial and radial temperatures distributions, temperatures gradient, visible flame length and species concentrations. The results indicated that as the air temperature increased, the chemical reaction rate increased and flame volume decreased, the combustion time reduced leading to a reduction in flame length. The NO concentration reaches its maximum values near the location of the maximum centerline axial temperature. Increasing the combustion air temperature by 200 K, the NO consequently O2 concentrations are increased by about % 355 and 20 % respectively, while CO2 and CO concentrations are decreased by about % 21 and 99 % respectively, at the combustor end.

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Flame Length Measurements of Burning Fuel Puffs

Combustion Science and Technology ◽

10.1080/00102209308935312 ◽

1993 ◽

Vol 94 (1-6) ◽

pp. 229-244 ◽

Cited By ~ 24

Author(s):

HAMID JOHARI ◽

VAHID MOTEVALLI

Keyword(s):

Flame Length ◽

Length Measurements

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The effects of wind on the flame characteristics of individual leaves

International Journal of Wildland Fire ◽

10.1071/wf10019 ◽

2011 ◽

Vol 20 (5) ◽

pp. 657 ◽

Cited By ~ 7

Author(s):

Wesley J. Cole ◽

McKaye H. Dennis ◽

Thomas H. Fletcher ◽

David R. Weise

Keyword(s):

Froude Number ◽

Flame Length ◽

Flame Height ◽

Combustion Model ◽

Small Scale ◽

Single Leaf ◽

Small Branch ◽

Flame Burner ◽

Broadleaf Species ◽

Semi Empirical

Individual cuttings from five shrub species were burned over a flat-flame burner under wind conditions of 0.75–2.80 m s–1. Both live and dead cuttings were used. These included single leaves from broadleaf species as well as 3 to 5 cm-long branches from coniferous and small broadleaf species. Flame angles and flame lengths were determined by semi-automated measurements of video images. Additional data, such as times and temperatures corresponding to ignition, maximum flame height and burnout were determined using video and infrared images. Flame angles correlated linearly with wind velocity. They also correlated with the Froude number when either the flame length or flame height was used. Flame angles in individual leaf experiments were generally 50 to 70% less than flame angles derived from Froude number correlations reported in the literature for fuel-bed experiments. Although flame angles increased with fuel mass and moisture content, they were unaffected by fuel species. Flame lengths and flame heights decreased with moisture contents and wind speed but increased with mass. In most cases, samples burned with wind conditions ignited less quickly and at lower temperatures than samples burned without wind. Most samples contained moisture at the time of ignition. Results of this small-scale approach (e.g. using individual cuttings) apply to ignition of shrubs and to flame propagation in shrubs of low bulk density. This research is one of the few attempts to characterise single-leaf and small-branch combustion behaviour in wind and is crucial to the continued development of a semi-empirical shrub combustion model.

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Effects of Acoustic Excitation on a Swirling Diffusion Flame

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4001768 ◽

2010 ◽

Vol 132 (12) ◽

Cited By ~ 8

Author(s):

Michael E. Loretero ◽

Rong F. Huang

Keyword(s):

Flow Field ◽

Bluff Body ◽

Excitation Frequency ◽

Excitation Amplitude ◽

Mie Scattering ◽

Flame Length ◽

Laser Doppler Velocimeter ◽

Scattering Method ◽

Acoustic Excitation ◽

Characteristic Modes

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

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Minimizing the cost of wildland fire suppression: a model with uncertainty in predicted flame length and fire-line width produced

Canadian Journal of Forest Research ◽

10.1139/x94-164 ◽

1994 ◽

Vol 24 (6) ◽

pp. 1253-1259 ◽

Cited By ~ 18

Author(s):

Romain Mees ◽

David Strauss ◽

Richard Chase

Keyword(s):

Line Width ◽

Wildland Fire ◽

Fire Suppression ◽

Flame Length ◽

Burned Area ◽

Expected Cost ◽

Control Time ◽

The Cost ◽

Attack Strategy

We describe a model that estimates the optimal total expected cost of a wildland fire, given uncertainty in both flame length and fire-line width produced. In the model, a sequence of possible fire-line perimeters is specified, each with a forecasted control time. For a given control time and fire line, the probability of containment of the fire is determined as a function of the fire-fighting resources available. Our procedure assigns the resources to the fire line so as to minimize the total expected cost. A key feature of the model is that the probabilities reflect the degree of uncertainty in (i) the width of fire line that can be built with a given resource allocation, and (ii) the flame length of the fire. The total expected cost associated with a given choice of fire line is the sum of: the loss or gain of value of the area already burned; the cost of the resources used in the attack; and the expected loss or gain of value beyond the fire line. The latter is the product of the probability that the chosen attack strategy fails to contain the fire and the value of the additional burned area that would result from such a failure. The model allows comparison of the costs of the different choices of fire line, and thus identification of the optimal strategy. A small case study is used to illustrate the procedure.

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Intraventricular flow visualization in different heart failure stages with blood pump support in a mock circulatory loop

The International Journal of Artificial Organs ◽

10.1177/03913988211021432 ◽

2021 ◽

pp. 039139882110214

Author(s):

Guang-Mao Liu ◽

Fu-Qing Jiang ◽

Jiang-Ping Song ◽

Sheng-Shou Hu

Keyword(s):

Heart Failure ◽

Standard Deviation ◽

Aortic Valve ◽

Left Ventricle ◽

Left Ventricular ◽

Blood Pump ◽

Blood Damage ◽

Intraventricular Flow ◽

Pump Inlet ◽

Strong Vorticity

The intraventricular blood flow changed by blood pump flow dynamics may correlate with thrombosis and ventricular suction. The flow velocity, distribution of streamlines, vorticity, and standard deviation of velocity inside a left ventricle failing to different extents throughout the cardiac cycle when supported by an axial blood pump were measured by particle image velocimetry (PIV) in this study. The results show slower and static flow velocities existed in the central region of the left ventricle near the mitral valve and aortic valve and that were not sensitive to left ventricular (LV) failure degree or LV pressure. Strong vorticity located near the inner LV wall around the LV apex and the blood pump inlet was not sensitive to LV failure degree or LV pressure. Higher standard deviation of the blood velocity at the blood pump inlet decreased with increasing LV failure degree, whereas the standard deviation of the velocity near the atrium increased with increasing intraventricular pressure. The experimental results demonstrated that the risk of thrombosis inside the failing left ventricle is not related to heart failure degree. The “washout” performance of the strong vorticity near the inner LV wall could reduce the thrombotic potential inside the left ventricle and was not related to heart failure degree. The vorticity near the aortic valve was sensitive to LV failure degree but not to LV pressure. We concluded that the risk of blood damage caused by adverse flow inside the left ventricle decreased with increasing LV pressure.

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Rotating co-flow jets with horizontal lip and shape transition

Aircraft Engineering and Aerospace Technology ◽

10.1108/aeat-05-2020-0095 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Dawn Pradeeb S. A. ◽

Subramanian Thanigaiarasu ◽

Nagarajakrishnan Premanand

Keyword(s):

Nozzle Exit ◽

Large Scale ◽

Metal Cutting ◽

Flame Length ◽

Equivalent Diameter ◽

Exit Plane ◽

Interesting Phenomenon ◽

Destructive Effect ◽

Outer Flow ◽

Content Type

Purpose Control over large-scale coherent structures and stream-wise vortices lead to enhanced entrainment/conservation of the jet which is desirable for most free jet applications such as design of combustion chamber in jet engines and flame length elongation of welding torch used for metal cutting. Design/methodology/approach A co-flow nozzle with lip thickness of 2 mm, between the primary (inner) and secondary (outer) flow, is selected. Three nozzle combinations are used, i.e. C–C (circle–circle), C–E (circle–ellipse) and C–S (circle–square) for acquiring comparative data. For these nozzle combinations, inner nozzle exit plane is kept as a circle, whereas the outer nozzle exit planes are varied to circle, ellipse and square. The exit plane area of outer nozzle for the nozzle combinations has equivalent diameter, De. The nozzles are fabricated in a way that the outer nozzle can be rotated along the longitudinal axis, keeping the inner nozzle intact. Findings The C–C nozzle combination is effective in low Mach number regime in decaying the jet, when the rotational component is introduced. Around 30% reduction in the jet core length is observed for the C–C nozzle combinations without any lip. The C–E nozzle shows sedative result in decaying or preserving the jet. The C–S nozzle combination shows interesting phenomenon, whereby the low subsonic case tends to conserve the jet by 15% and the higher subsonic case tends to decay the jet by 10%. Originality/value The developed nozzle systems show both conservative and destructive effect on the jet, which is desirable for the mentioned applications.

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