slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Physical sub-models to be included in the main model PowerPoint Presentation
Download Presentation
Physical sub-models to be included in the main model

Loading in 2 Seconds...

play fullscreen
1 / 18

Physical sub-models to be included in the main model - PowerPoint PPT Presentation


  • 109 Views
  • Uploaded on

Physical sub-models to be included in the main model. In Physical Modelling the conservation equations (mass, momentum, energy) are solved. Observations, experiments, and modelling show that there is gas flow. ... ahead of the flame near the fuel bed. Bellemare, 2000.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Physical sub-models to be included in the main model' - ainsley-odom


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Physical sub-models to be included in the main model

In Physical Modelling the conservation equations

(mass, momentum, energy) are solved

Observations, experiments, and modelling

show that there is gas flow ...

... ahead of the flame near the fuel bed ...

Bellemare, 2000

... and inside the porous fuel bed

Obviously, there is also flow inside shrubs and inside foliage

Fire Star conclusive symposium: Marseille March 18th 2005

slide2

Physical sub-models to be included in the main model

Several sub-models are used to deal with a number of phenomena

The temperatures of fuel bed, shrubs, foliage, and of the gas

that flows inside them are not necessarely the same

  • heat transfer between the gas and these fuel matrixes occurs

This energy exchange plays an important role in the

decrease of fuel moisture content and in the fuel pyrolysis

The flow inside the fuel matrices is subjected to aerodynamic drag

  • sub-models for heat transfer and aerodynamic drag are,
  • therefore, necessary

Fire Star conclusive symposium: Marseille March 18th 2005

slide3

Physical sub-models to be included in the main model

There is no data on porous beds similar to forest fire fuel matrices

Data on packed beds from chemical engineering have been used

... chemical packed beds are very different from

the forest fuel matrices

But ...

Objective :

  • to measure the heat transfer coefficient h and pressure drop
  • through matrices of forest fuels

Fire Star conclusive symposium: Marseille March 18th 2005

slide4

heating elements

working section

+

2

Existing wind tunel

heating elements

(used for aerodynamic studies  very good performance)

+

honeycomb

pine needles

+

honeycomb

1

honeycomb

3

heating elements

working section

+

o

o

o

o

o

o

4

thermocouple

honeycomb

pine needles

pressure tap

Physical sub-models to be included in the main model

Section 1 : electric resistances (5 kW) to heat the flow

Section 2 : working section packed with pine needles

or twigs and leaves

or just twigs

1000 x 160 x 240 mm (l x h x w)

insulated walls

6 thermocouples and pressure taps

Fire Star conclusive symposium: Marseille March 18th 2005

slide5

Physical sub-models to be included in the main model

Thin thermocouples had to be “inserted” at the fuel surfaces

Thicker wire (250m) to which the thin wire is attached

125m K type thermocouple “inserted” at the fuel particle’s surface

125m K type thermocouple in the air at the vicinity of the fuel particle

Fire Star conclusive symposium: Marseille March 18th 2005

slide6

D 4 / SVR

h = Nu = Nu

k k

Physical sub-models to be included in the main model

Examples of the curves obtained for h and for pressure drop

Pressure drop per unit length

for Quercus coccifera

Nu as a function of Re for

Pinus pinaster and Quercus coccifera

Influence of the strata location

and existence (or not) of leaves

Fire Star conclusive symposium: Marseille March 18th 2005

slide7

Experimental fires in the INIA wind tunnel

  • Experimental fires in the wind tunnelwere devoted to:
    • Validate the behaviour model of wildland fire
    • Analyse effectsof
      • Wind speed
      • Shrub moisture content
      • Width of a discontinuity
      • on the fire behaviour
    • in a fuel complex of Pinus pinaster litter
    • and Chamaespartium tridentatum shrubs

General view of

INIA wind tunnel

Fire Star conclusive symposium: Marseille March 18th 2005

slide8

C. tridentatum shrubs

P. pinaster litter

Experimental fires in the INIA wind tunnel

  • Example of test :
    • Wind speed = 1 m/s
    • Shrub m.c.: 40 %
    • Width of discontinuity = 0 m

Fire Star conclusive symposium: Marseille March 18th 2005

experimental fires in the inia wind tunnel
Experimental fires in the INIA wind tunnel
  • Example of Test on discontinuous fuel:
      • Wind speed = 0 m/s
      • Shrub m.c.: 40 %
      • Width of discontinuity = 2 m

Fire Star conclusive symposium: Marseille March 18th 2005

slide10

Variation of Maximum Temperatures with Height

Experimental fires in the INIA wind tunnel

Examples of results obtained at INIA wind tunnel

Width of discontinuity = 0 m

Variation of Rate of Spread with Wind Speed

Similar set of results are available for:

* Flame height

* Byram´s fireline intensity

Fire Star conclusive symposium: Marseille March 18th 2005

slide11

Visible

TIR (8-12 m)

MIR (3-5 m)

Multi-

spectral

TIR

MIR

  • LIR-UC3MFire parameters obtained by IR Spectral Imaging
  • Equipment set up and Images Acquisition
  • Tunnel and lab meas.: 2 cameras one for each band (MIR &TIR).
  • Field measurements: 1 camera: up to 4 MIR sub-bands

Infrared images are simultaneous, co-registered and calibrated (brightness temperatures)

Bi-spectral images (MIR & TIR bands)

Multispectral images (4 MIR bands)

Fire Star conclusive symposium: Marseille March 18th 2005

slide12

T (K)

LIR-UC3MFire parameters obtained by IR Spectral Imaging

2. Pixel Classification and image processing

IR image: Physical parameters measured

  • Brigthness temperatures
  • Scene classification
  • Rate of spread
  • IR flame height
  • Instantaneous Radiated power
  • Estimation of:
    • Total released power (roughly, 17% of the power released is radiated)
    • Fire front intensity
    • Heat released per unit area

MIR

Bi-spectral image

T (K)

TIR

Class

map

(For multispectral images is analogous)

In collaboration with INIA and CIF-Lourizan

Fire Star conclusive symposium: Marseille March 18th 2005

slide13

gases

CO2

CO

IR emitter

FTIR

Fuel sample

Heater

CH4

LIR-UC3M Fuel Pyrolysis Studies based on FTIRS- Fourier Transform IR Spectrometry: 1. Schematics and aims

spectral absorbance

  •  Objective: to gain knowledge on the pyrolysis chemistry
  • FTIR spectrometry:

a) identification of gases by the spectral location of absorbance bands

b) determination of gas concentration from the band depth

  • c) acquires simultaneously information on the whole spectral range (2-16 mm)
  • Gases under study: CO2 , CO , CH4 , NH3

In collaboration with INIA

Fire Star conclusive symposium: Marseille March 18th 2005

slide14

combustion efficiency

  • - clear correlation of NH3 with CO emissions
  • data dispersion
  • low rate of CH4 emission

LIR-UC3M Fuel Pyrolysis Studies based on FTIRS

2. Some remarkable results

In collaboration with INIA

Fire Star conclusive symposium: Marseille March 18th 2005

sketch of the experiment

INRA

DESIRE bench

5 thermocouplesonto a vertical

Sketch of the experiment

UP VIEW

median axis of DESIRE

camera field of view

DESIRE plate

infrared camera

SIDE VIEW

Fire Star conclusive symposium: Marseille March 18th 2005

comparison of infrared signal and thermocouple temperature near fire front

INRA

DESIRE bench

1 pixel of the infrared image

solid fuel temperature

comparison of time signals

Comparison of infrared signal and thermocouple temperature near fire front

position of the cotton thread

position du fil de coton

thermocouple at 5 cm high gas temperature

thermocouple à 5 cm de haut  température du gaz

Fire Star conclusive symposium: Marseille March 18th 2005

time evolutions of solid fuel and gas temperature slope 0

INRA

DESIRE bench

Time evolutions of solid fuel and gas temperature – Slope

Slope 0° Pente 0°

Moyenne mobile

des données de température

the thermocouple ‘enters’ the flame

le thermocouple ‘entre’ dans la flamme

Pre-heating of the litter

Préchauffage de la litière

solid fuel temperature  gas temperature

Breaking of the cotton thread

Coupure du fil de coton

Fire Star conclusive symposium: Marseille March 18th 2005

slide18

INRA

DESIRE bench

Time evolutions of solid fuel and gas temperature – Slope 30°

Slope 30° Pente 30°

the thermocouple ‘enters’ the flame

le thermocouple ‘entre’ dans la flamme

Pre-heating of the litter

Préchauffage de la litière

solid fuel temperature  gas temperature

Breaking of the cotton thread

Coupure du fil de coton

Fire Star conclusive symposium: Marseille March 18th 2005