Re-analysis of wind and slope effects on flame characteristics of Mediterranean shrub fires

2015 ◽  
Vol 24 (7) ◽  
pp. 1001 ◽  
Author(s):  
Ralph M. Nelson
Keyword(s):  
Heat Transfer ◽  
Wildland Fire ◽  
Physical Modelling ◽  
Field Measurements ◽  
Heat Fluxes ◽  
Flame Height ◽  
Fire Behaviour ◽  
Dimensionless Variables ◽  
Mediterranean Shrub ◽  
Experimental Burns

During the past 20 years, study of wind–slope-aided wildland fire behaviour with experimental burns and physical modelling methods has increased. As part of their continuing study of fires in Mediterranean shrub, F. Morandini and X. Silvani reported experimental temperatures, heat fluxes, flame characteristics and other fire behaviour variables measured on five wind–slope-aided fires. Calculating convection numbers and several convective Froude numbers, the authors concluded that these dimensionless variables for their two wind-dominated fires did not satisfy criteria identified in previous studies for determining mechanisms of heat transfer during fuel preheating. The present paper describes a re-analysis of the data based on a triangular flame model and alternative definitions of flame tilt angle and height. This new analysis has shown that the influence of slope on the fire behaviour was not accounted for; thus, the conclusion of Morandini and Silvani is questionable. Of the five dimensionless variables studied using criteria in the literature, the squared flame height convective Froude number best describes modes of heat transfer to unburned fuels during the experimental fires. Though these results come indirectly from field measurements, they confirm the need to include slope effects in descriptions of wind–slope-aided fire behaviour.

scholarly journals An analytical model of icicle growth

1994 ◽  
Vol 19 ◽  
pp. 141-145 ◽  
Author(s):  
Krzysztof Szilder ◽  
Edward P. Lozowski
Keyword(s):  
Heat Transfer ◽  
Analytical Solution ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Differential Forms ◽  
Heat Fluxes ◽  
Time Interval ◽  
Dimensionless Form ◽  
Conservation Of Energy ◽  
Dimensionless Variables

A model of icicle growth has been developed based on an analytical solution of the differential forms of the conservation of energy and mass. The problem has been formulated using dimensionless variables defined as the ratios of the various heat fluxes which determine the icicle’s growth. The evolution of the dimensionless icicle shape has been expressed as a function of the variation of the convective heat transfer with icicle radius. The time interval needed for the icicle to reach its maximum length and the variation of the icicle mass and drip rate are expressed in dimensionless form.

Interdependencies between flame length and fireline intensity in predicting crown fire initiation and crown scorch height

2012 ◽  
Vol 21 (2) ◽  
pp. 95 ◽  
Author(s):  
Martin E. Alexander ◽  
Miguel G. Cruz
Keyword(s):  
Wildland Fire ◽  
Stem Bark ◽  
Flame Length ◽  
Flame Height ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Surface Fire ◽  
Crown Scorch ◽  
Fire Initiation ◽  
Bark Char

This state-of-knowledge review examines some of the underlying assumptions and limitations associated with the inter-relationships among four widely used descriptors of surface fire behaviour and post-fire impacts in wildland fire science and management, namely Byram’s fireline intensity, flame length, stem-bark char height and crown scorch height. More specifically, the following topical areas are critically examined based on a comprehensive review of the pertinent literature: (i) estimating fireline intensity from flame length; (ii) substituting flame length for fireline intensity in Van Wagner’s crown fire initiation model; (iii) the validity of linkages between the Rothermel surface fire behaviour and Van Wagner’s crown scorch height models; (iv) estimating flame height from post-fire observations of stem-bark char height; and (v) estimating fireline intensity from post-fire observations of crown scorch height. There has been an overwhelming tendency within the wildland fire community to regard Byram’s flame length–fireline intensity and Van Wagner’s crown scorch height–fireline intensity models as universal in nature. However, research has subsequently shown that such linkages among fire behaviour and post-fire impact characteristics are in fact strongly influenced by fuelbed structure, thereby necessitating consideration of fuel complex specific-type models of such relationships.

Corrigendum to: Interdependencies between flame length and fireline intensity in predicting crown fire initiation and crown scorch height

2017 ◽  
Vol 26 (4) ◽  
pp. 345 ◽  
Author(s):  
Martin E. Alexander ◽  
Miguel G. Cruz
Keyword(s):  
Wildland Fire ◽  
Stem Bark ◽  
Flame Length ◽  
Flame Height ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Surface Fire ◽  
Crown Scorch ◽  
Fire Initiation ◽  
Bark Char

This state-of-knowledge review examines some of the underlying assumptions and limitations associated with the inter-relationships among four widely used descriptors of surface fire behaviour and post-fire impacts in wildland fire science and management, namely Byram's fireline intensity, flame length, stem-bark char height and crown scorch height. More specifically, the following topical areas are critically examined based on a comprehensive review of the pertinent literature: (i) estimating fireline intensity from flame length; (ii) substituting flame length for fireline intensity in Van Wagner's crown fire initiation model; (iii) the validity of linkages between the Rothermel surface fire behaviour and Van Wagner's crown scorch height models; (iv) estimating flame height from post-fire observations of stem-bark char height; and (v) estimating fireline intensity from post-fire observations of crown scorch height. There has been an overwhelming tendency within the wildland fire community to regard Byram's flame length–fireline intensity and Van Wagner's crown scorch height–fireline intensity models as universal in nature. However, research has subsequently shown that such linkages among fire behaviour and post-fire impact characteristics are in fact strongly influenced by fuelbed structure, thereby necessitating consideration of fuel complex specific-type models of such relationships.

A variable property heat transfer model for predicting soil temperature profiles during simulated wildland fire conditions

2008 ◽  
Vol 17 (2) ◽  
pp. 205 ◽  
Author(s):  
Ebenezer K. Enninful ◽  
David A. Torvi
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Wildland Fire ◽  
Heat Fluxes ◽  
Transfer Model ◽  
Temperature Dependent ◽  
Heat Penetration ◽  
Experimental Values ◽  
Temperature Dependent Properties ◽  
Plant Shoots

A numerical model of heat transfer in dry soil was developed to predict temperatures and depth of lethal heat penetration during cone calorimeter tests used to simulate wildland fire exposures. The model was used to compare predictions made using constant and temperature-dependent thermal properties with experimental results for samples of dry sand exposed to heat fluxes of 25, 50 and 75 kW m–2. Depths of lethal heat penetration predicted using temperature-dependent properties were within 2 to 10% of the values determined using measured temperatures, while predictions made using constant properties were within 10 to 21% of the experimental values. In both cases, predictions made by the model were within the 1-cm accuracy with which the depth of seeds and plant shoots in the soil can be determined in practice. The model generally over-predicted the depth of lethal heat penetration in dry or moist soil when temperature-dependent properties were used, and over-predicted the depth of lethal heat penetration in soils with a moisture content of greater than 10% if constant thermal properties were used.

On the need for a theory of wildland fire spread

2013 ◽  
Vol 22 (1) ◽  
pp. 25 ◽  
Author(s):  
Mark A. Finney ◽  
Jack D. Cohen ◽  
Sara S. McAllister ◽  
W. Matt Jolly
Keyword(s):  
Heat Transfer ◽  
Fire Management ◽  
Wildland Fire ◽  
Fire Spread ◽  
Fire Behaviour ◽  
Fire Models ◽  
Model Reliability ◽  
The Difference ◽  
Combustion Processes ◽  
Common Understanding

We explore the basis of understanding wildland fire behaviour with the intention of stimulating curiosity and promoting fundamental investigations of fire spread problems that persist even in the presence of tremendous modelling advances. Internationally, many fire models have been developed based on a variety of assumptions and expressions for the fundamental heat transfer and combustion processes. The diversity of these assumptions raises the question as to whether the absence of a sound and coherent fire spread theory is partly responsible. We explore the thesis that, without a common understanding of what processes occur and how they occur, model reliability cannot be confirmed. A theory is defined as a collection of logically connected hypotheses that provide a coherent explanation of some aspect of reality. Models implement theory for a particular purpose, including hypotheses of phenomena and practical uses, such as prediction. We emphasise the need for theory and demonstrate the difference between theory and modelling. Increasingly sophisticated fire management requires modelling capabilities well beyond the fundamental basis of current models. These capabilities can only be met with fundamental fire behaviour research. Furthermore, possibilities as well as limitations for modelling may not be known or knowable without first having the theory.

scholarly journals An analytical model of icicle growth

1994 ◽  
Vol 19 ◽  
pp. 141-145 ◽  
Author(s):  
Krzysztof Szilder ◽  
Edward P. Lozowski
Keyword(s):  
Heat Transfer ◽  
Analytical Solution ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Differential Forms ◽  
Heat Fluxes ◽  
Time Interval ◽  
Dimensionless Form ◽  
Conservation Of Energy ◽  
Dimensionless Variables

A model of icicle growth has been developed based on an analytical solution of the differential forms of the conservation of energy and mass. The problem has been formulated using dimensionless variables defined as the ratios of the various heat fluxes which determine the icicle’s growth. The evolution of the dimensionless icicle shape has been expressed as a function of the variation of the convective heat transfer with icicle radius. The time interval needed for the icicle to reach its maximum length and the variation of the icicle mass and drip rate are expressed in dimensionless form.

Improvement Of Free Convection From Three horizontal Finned Cylinders Fixed Between Two Walls

2018 ◽  
Vol 6 (2) ◽  
pp. 98-114 ◽  
Author(s):  
Hassan K. Abdullah ◽  
Haneen H. Rahman
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Prandtl Number ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Head Orientation ◽  
Outer Diameter ◽  
Gravitational Acceleration ◽  
Convection Heat

Improvement of  free convection heat transfer from three finned cylinders arranged at a triangle shape fixed between two walls has been investigated in this study. Three mild steel finned cylinders fixed between two walls from Pyrex glass have been used as a test rig. It has been changed the spacing between the cylinders (X/D=1,2,3 & S/D=2,4,6) and the head orientation of a triangle to the top under constant heat flux values (38, 254, 660, 1268) W/m2 and compare with case of three finned cylinders arranged in vertical array in line fixed between two wall. The experiments are carried for Rayleigh number (Ra) from (15x103 to 14 x104 ) and Prandtl  number from (0.706-0.714 ). The results indicated an increase in Nu with increasing Ra for all cylinders. Furthermore,hx and Nu increased proportionally with the increasing of cylinder spacings for all heat fluxes. Also the experimental results show the case of triangle arrangement is improvement the heat transfer more than case of vertical arrangement. Heat transfer dimensionless correlating equation is also proposed.              Nomeclature: Ax: surface area(m2), T∞: surrounding temperature(k), D: the outer diameter of fin (m), Kf: the thermal conductivity for air at film temperature(W/m.k), hx: Local convection heat transfer(W/m2.k),  Gravitational acceleration(m/s2), I: Electric current (Amp), Nu: Nusselt number, Pr: Prandtl number

scholarly journals Assessing IDDES-Based Wall-Modeled Large-Eddy Simulation (WMLES) for Separated Flows with Heat Transfer

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 246
Author(s):  
Rozie Zangeneh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Large Eddy Simulation ◽  
Skin Friction ◽  
Heat Fluxes ◽  
Separated Flows ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Isothermal Wall

The Wall-modeled Large-eddy Simulation (WMLES) methods are commonly accompanied with an underprediction of the skin friction and a deviation of the velocity profile. The widely-used Improved Delayed Detached Eddy Simulation (IDDES) method is suggested to improve the prediction of the mean skin friction when it acts as WMLES, as claimed by the original authors. However, the model tested only on flow configurations with no heat transfer. This study takes a systematic approach to assess the performance of the IDDES model for separated flows with heat transfer. Separated flows on an isothermal wall and walls with mild and intense heat fluxes are considered. For the case of the wall with heat flux, the skin friction and Stanton number are underpredicted by the IDDES model however, the underprediction is less significant for the isothermal wall case. The simulations of the cases with intense wall heat transfer reveal an interesting dependence on the heat flux level supplied; as the heat flux increases, the IDDES model declines to predict the accurate skin friction.

scholarly journals Pool Boiling Heat Transfer Coefficients in Mixtures of Water and Glycerin

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Viktor Vajc ◽  
Radek Šulc ◽  
Martin Dostál
Keyword(s):  
Heat Transfer ◽  
Dynamic Method ◽  
Water Mass ◽  
Heat Fluxes ◽  
Static Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mean Relative Error ◽  
Mixture Effects ◽  
Mass Fractions

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

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