Thermodynamic structure of a grass fire plume

2010 ◽  
Vol 19 (7) ◽  
pp. 895 ◽  
Author(s):  
Craig B. Clements
Keyword(s):  
Short Duration ◽  
Combustion Zone ◽  
Rapid Heating ◽  
Ground Level ◽  
Heating Rates ◽  
Fire Plume ◽  
Thermodynamic Structure ◽  
Rate Of Spread ◽  
Fire Front ◽  
Plume Temperature

High-frequency thermocouple measurements were made during an experimental grass fire conducted during ideal weather with overcast and windy conditions. Analysis of the thermodynamic structure of the fire plume showed that a maximum plume temperature of 295.2°C was measured directly above the combustion zone. Plume heating rates were on the order of 26–45 kW m–2 and occurred in the region just above the combustion zone between 10 and 15 m above ground level and were followed by cooling of approximately –37 and –44 kW m–2. The observed cooling was caused by strong entrainment that occurred behind the fire front and plume. The rapid heating and subsequent cooling indicate that the heating caused by a fire front is limited to a small volume around the flaming front and that the rates of heat gain occur for a short duration. The short duration of plume heating is due to the fast rate of spread of the fire front and ambient wind.

scholarly journals Evaluation of WRF-SFIRE performance with field observations from the FireFlux experiment

2013 ◽  
Vol 6 (4) ◽  
pp. 1109-1126 ◽  
Author(s):  
A. K. Kochanski ◽  
M. A. Jenkins ◽  
J. Mandel ◽  
J. D. Beezley ◽  
C. B. Clements ◽  
...  
Keyword(s):  
Wind Speed ◽  
Ground Level ◽  
Surface Flow ◽  
Horizontal Wind ◽  
Temperature Structure ◽  
Fire Plume ◽  
Arrival Times ◽  
Wind Speeds ◽  
Rate Of Spread ◽  
Fire Front

Abstract. This study uses in situ measurements collected during the FireFlux field experiment to evaluate and improve the performance of the coupled atmosphere–fire model WRF-SFIRE. The simulation by WRF-SFIRE of the experimental burn shows that WRF-SFIRE is capable of providing realistic head-fire rate of spread and vertical temperature structure of the fire plume, and fire-induced surface flow and vertical velocities within the plume up to 10 m above ground level. The simulation captured the changes in wind speed and direction before, during, and after fire front passage, along with the arrival times of wind speed, temperature, and updraft maxima, at the two instrumented flux towers used in FireFlux. The model overestimated vertical wind speeds and underestimated horizontal wind speeds measured at tower heights above 10 m. It is hypothesized that the limited model spatial resolution led to overestimates of the fire front depth, heat release rate, and updraft speed. However, on the whole, WRF-SFIRE simulated fire plume behavior that is consistent with FireFlux observations. The study suggests optimal experimental pre-planning, design, and execution strategies for future field campaigns that are intended to evaluate and develop further coupled atmosphere–fire models.

scholarly journals Evaluation of WRF-SFIRE performance with field observations from the FireFlux experiment

2013 ◽  
Vol 6 (1) ◽  
pp. 121-169 ◽  
Author(s):  
A. K. Kochanski ◽  
M. A. Jenkins ◽  
J. Mandel ◽  
J. D. Beezley ◽  
C. B. Clements ◽  
...  
Keyword(s):  
Wind Speed ◽  
Model Development ◽  
Ground Level ◽  
Surface Flow ◽  
Horizontal Wind ◽  
Temperature Structure ◽  
Fire Plume ◽  
Fire Model ◽  
Wind Speeds ◽  
Fire Front

Abstract. This study uses in-situ measurements collected during the FireFlux field experiment to evaluate and improve the performance of coupled atmosphere-fire model WRF-SFIRE. The simulation of the experimental burn shows that WRF-SFIRE is capable of providing realistic head fire rate-of-spread and the vertical temperature structure of the fire plume, and, up to 10 m above ground level, fire-induced surface flow and vertical velocities within the plume. The model captured the changes in wind speed and direction before, during, and after fire front passage, along with arrival times of wind speed, temperature, and updraft maximae, at the two instrumented flux towers used in FireFlux. The model overestimated vertical velocities and underestimated horizontal wind speeds measured at tower heights above the 10 m, and it is hypothesized that the limited model resolution over estimated the fire front depth, leading to too high a heat release and, subsequently, too strong an updraft. However, on the whole, WRF-SFIRE fire plume behavior is consistent with the interpretation of FireFlux observations. The study suggests optimal experimental pre-planning, design, and execution of future field campaigns that are needed for further coupled atmosphere-fire model development and evaluation.

Probing boron thermite energy release at rapid heating rates

2021 ◽  
Vol 231 ◽  
pp. 111491
Author(s):  
Jennifer L. Gottfried ◽  
Elliot R. Wainwright ◽  
Sidi Huang ◽  
Yue Jiang ◽  
Xiaolin Zheng
Keyword(s):  
Energy Release ◽  
Rapid Heating ◽  
Heating Rates

Fine-Scale Fire Spread in Pine Straw

Fire ◽  
2021 ◽  
Vol 4 (4) ◽  
pp. 69
Author(s):  
Daryn Sagel ◽  
Kevin Speer ◽  
Scott Pokswinski ◽  
Bryan Quaife
Keyword(s):  
Fire Spread ◽  
Small Scale ◽  
Natural Setting ◽  
Fine Scale ◽  
Prescribed Burn ◽  
Fire Dynamics ◽  
Rate Of Spread ◽  
Scale Models ◽  
Fire Front ◽  
Visible Images

Most wildland and prescribed fire spread occurs through ground fuels, and the rate of spread (RoS) in such environments is often summarized with empirical models that assume uniform environmental conditions and produce a unique RoS. On the other hand, representing the effects of local, small-scale variations of fuel and wind experienced in the field is challenging and, for landscape-scale models, impractical. Moreover, the level of uncertainty associated with characterizing RoS and flame dynamics in the presence of turbulent flow demonstrates the need for further understanding of fire dynamics at small scales in realistic settings. This work describes adapted computer vision techniques used to form fine-scale measurements of the spatially and temporally varying RoS in a natural setting. These algorithms are applied to infrared and visible images of a small-scale prescribed burn of a quasi-homogeneous pine needle bed under stationary wind conditions. A large number of distinct fire front displacements are then used statistically to analyze the fire spread. We find that the fine-scale forward RoS is characterized by an exponential distribution, suggesting a model for fire spread as a random process at this scale.

Modeling on n-Heptane Pool Fire Behavior in an Altitude Chamber

2013 ◽  
Author(s):  
Quanyi Liu ◽  
Wei Yao ◽  
Jiusheng Yin ◽  
Rui Yang ◽  
Hui Zhang
Keyword(s):  
High Altitude ◽  
Burning Rate ◽  
Pressure Effect ◽  
Fire Behavior ◽  
Low Pressure ◽  
Pool Fire ◽  
Low Oxygen ◽  
Fire Plume ◽  
Plume Temperature ◽  
Modeling Data

Airplane as one of the important transport vehicles in our life, its safety problem related to in-flight fire has attracted a wide-spread attention. The combustion behavior of the cabin fire in flight shows some special characteristics because of the high-altitude environment with low-pressure and low oxygen concentration. A low-pressure chamber of size 2 m×3 m×2 m has been built to simulate high-altitude environments, where multiple static pressures for pool fire tests can be configured in the range between standard atmospheric pressure 101.3KPa and 30KPa. Two different sizes of pool fires were tested. Then corresponding modeling were conducted by a LES code FDS V5.5 to examine the mechanism of pressure effect on the n-Heptane pool fire behavior. The burning of liquid fuel was modeled by a Clausius-Clapeyron relation based liquid pyrolysis model. The modeling data was validated against the experimental measurements. The mass burning rate of free-burning pool fire decreases with the decreasing of pressure, which was observed from the modeling to be due to the reduction of flame heat feedback to the fuel surface. Under low pressure, the fire plume temperature increases for the same burning rate. The mechanism of pressure effect on fire behavior was analyzed based on the modeling data.

High Productivity Thermo-Compression Flip Chip Bonding

2014 ◽  
Vol 2014 (1) ◽  
pp. 000100-000106
Author(s):  
Tom Colosimo ◽  
Horst Clauberg ◽  
Evan Galipeau ◽  
Matthew B. Wasserman ◽  
Michael Schmidt-Lange ◽  
...  
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Flip Chip ◽  
Solder Joints ◽  
Rapid Heating ◽  
Temperature Cycle ◽  
Temperature Uniformity ◽  
Heating Rates ◽  
Heating And Cooling ◽  
Chip Technology

Advancements in electronic packaging performance and cost have historically been driven by higher integration primarily provided by fab shrinks that has followed the well-known Moore's law. However, due to the tremendous and continuously increasing cost of building new fabs, the performance/cost improvements achieved via node shrinks are negated. This leaves packaging innovation as the vehicle to achieve future cost-performance improvements. This has initiated a More-than-Moore idea that has led to vigorous R&D in packaging. Advanced packages which employ ultra-fine pitch flip chip technology for chip-to-substrate, chip-to-chip, or chip-to-interposer for the first level interconnect have been developed as an answer to obtaining higher performance. However, the costs are too high as compared to traditional wire bonding. The status today is that the fundamental technical hurdles of manufacturing the new advanced packages have been solved, but cost reduction and yield improvements have to be addressed for large-scale adoption into high volume manufacturing. In traditional flip chip assembly silicon chips are tacked onto a substrate and then the solder joints are melted and mass reflowed in an oven. This mass reflow technique is troublesome as the pitch of the solder bumps become finer. This is due to the large differences in the thermal expansion coefficient of the die and the substrate, which creates stress at the solder joints and warpage of the package when the die and substrate are heated and cooled together. To mitigate and resolve this issue, thermo-compression bonders have been developed which locally reflow the solder without subjecting the entire substrate to the heating and cooling cycle. This requires that the bondhead undergo heating past the melting point of solder and then cooling down to a low enough temperature to pick the next die from the wafer that is mounted to tape. Machines in the market today can accomplish this temperature cycle in 7 to 15 seconds. This is substantially slower than the standard flip chip process which leads to high cost and is delaying the introduction of these new packages. This paper shows a flip chip bonder with a new heating and cooling concept that will radically improve the productivity of thermo-compression bonding. Data and productivity cycles from this new bond head with heating rates of over 200°C/sec and cooling of faster than 100°C/sec are revealed. Experimental results are shown of exceptional temperature accuracy across the die of 5°C throughout the cycle and better than 3°C at the final heating stage. The high speed thermo-compression bonds are analyzed and the efficacy of the new concept is proven. Excellent temperature uniformity while heating rapidly is an absolute necessity for enabling good solder joints in a fast process. Without good temperature uniformity, additional dwell times need to be incorporated to allow heat to flow to all of the joints, negating any benefits from rapid heating. Whereas the current state-of-that-art is often to program temperature in steps, this bonder can be commanded and accurately follows more complex temperature profiles with great accuracy. Examples of how this profiling can be used to enhance the uniformity and integrity of the joints with non-conductive pastes, film, and without underfill along with the associated productivity improvements will be shown. Tests that show portability across platforms that will lead to set up time and yield improvements and are identified and quantified. Additionally new ideas for materials and equipment development to further enhance productivity and yield are explored.

Simulation study of grass fire using a physics-based model: striving towards numerical rigour and the effect of grass height on the rate of spread

2018 ◽  
Vol 27 (12) ◽  
pp. 800 ◽  
Author(s):  
K. A. M. Moinuddin ◽  
D. Sutherland ◽  
W. Mell
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Heat Release ◽  
Bulk Density ◽  
Simulation Study ◽  
Release Rate ◽  
Rate Of Spread ◽  
Fire Front ◽  
Physics Based Simulation ◽  
Mode A

Grid-independent rate of spread results from a physics-based simulation are presented. Previously, such a numerical benchmark has been elusive owing to computational restrictions. The grid-converged results are used to systematically construct correlations between the rate of spread (RoS) and both wind speed and grass height, separately. The RoS obtained from the physics-based model is found to be linear with wind speed in the parameter range considered. When wind speed is varied, the physics-based model predicts faster RoS than the Mk III and V (McArthur) models (Noble et al. 1980) but slower than the CSIRO model (Cheney et al. 1998). When the grass height is varied keeping the bulk density constant, the fire front changes from a boundary layer flame mode to plume flame mode as the grass height increases. Once the fires are in plume mode, a higher grass height results in a larger heat release rate of the fire but a slower RoS.

Laboratory fire spread analysis using visual and infrared images

2006 ◽  
Vol 15 (2) ◽  
pp. 179 ◽  
Author(s):  
J. Ramiro Martínez-de Dios ◽  
Jorge C. André ◽  
João C. Gonçalves ◽  
Begoña Ch. Arrue ◽  
Aníbal Ollero ◽  
...  
Keyword(s):  
Graphical Model ◽  
Fire Spread ◽  
Rate Of Spread ◽  
Virtual View ◽  
Fire Front ◽  
Computer Based ◽  
Front Shape ◽  
Processing Techniques ◽  
Spread Analysis ◽  
Base Width

This paper presents an experimental method using computer-based image processing techniques of visual and infrared movies of a propagating fire front, taken from one or more cameras, to supply the time evolutions of the fire front shape and position, flame inclination angle, height, and base width. As secondary outputs, it also provides the fire front rate of spread and a 3D graphical model of the fire front that can be rendered from any virtual view. The method is automatic and non-intrusive, has space–time resolution close to continuum and can be run in real-time or deferred modes. It is demonstrated in simple laboratory experiments in beds of pine needles set upon an inclinable burn table, with point and linear ignitions, but can be extended to open field situations.

scholarly journals Flame structures and ignition characteristics of torrefied and raw sewage sludge particles at rapid heating rates

Fuel ◽  
2017 ◽  
Vol 200 ◽  
pp. 467-480 ◽  
Author(s):  
Chinsung Mock ◽  
Hookyung Lee ◽  
Sangmin Choi ◽  
Vasilije Manovic
Keyword(s):  
Sewage Sludge ◽  
Rapid Heating ◽  
Heating Rates ◽  
Flame Structures ◽  
Ignition Characteristics

scholarly journals Heating of Ti3C2Tx MXene/polymer composites in response to Radio Frequency fields

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Touseef Habib ◽  
Nutan Patil ◽  
Xiaofei Zhao ◽  
Evan Prehn ◽  
Muhammad Anas ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Thermal Imaging ◽  
Electromagnetic Waves ◽  
Rapid Heating ◽  
Composite Films ◽  
Heating Rates ◽  
New Material ◽  
High Dielectric ◽  
First Time ◽  
Percolating Network

Abstract Here we report for the first time that Ti3C2Tx/polymer composite films rapidly heat when exposed to low-power radio frequency fields. Ti3C2Tx MXenes possess a high dielectric loss tangent, which is correlated with this rapid heating under electromagnetic fields. Thermal imaging confirms that these structures are capable of extraordinary heating rates (as high as 303 K/s) that are frequency- and concentration-dependent. At high loading (and high conductivity), Ti3C2Tx MXene composites do not heat under RF fields due to reflection of electromagnetic waves, whereas composites with low conductivity do not heat due to the lack of an electrical percolating network. Composites with an intermediate loading and a conductivity between 10–1000 S m−1 rapidly generate heat under RF fields. This finding unlocks a new property of Ti3C2Tx MXenes and a new material for potential RF-based applications.

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