Rak Fire simulation

Transcription

1 Rak Fire simulation 7. lecture Kaiyan Li Simo Hostikka

2 Learning objectives 1. Pyrolysis models in FDS. 2. TGA analysis. 3. Cone calorimeter. 3/2/2016 2

3 Pyrolysis models Simple Pyrolysis Models - A Gas Burner with a Specified Heat Release Rate - Special Topic: A Radially-Spreading Fire - Solid Fuels that Burn at a Specified Rate Complex Pyrolysis Model - Real materials burning process 3/2/2016 3

4 Complex Pyrolysis Model Real materials burning process Chemical (decomposition) Physical (heat transfer) 3/2/2016 4

5 Complex Pyrolysis Model Heat transfer modelling Heat of pyrolysis = + The decomposition is determined by the nodes temperatures x MATL ID = 'PF resin' SPECIFIC_HEAT_RAMP = 'c_wood' CONDUCTIVITY_RAMP = 'k_wood' DENSITY = 903 N_REACTIONS = 1 NU_RESIDUE = 0.2 NU_FUEL = 0.8 NU_WATER = 0.0 A = 3.76E+14 E = N_S = 3.80E+00 RESIDUE ='CHAR' HEAT_OF_REACTION = HEAT_OF_COMBUSTION = / 3/2/2016 5

6 Complex Pyrolysis Model Please see User Guide and Technical Guide Heat conduction Pyrolysis Use STRETCH_FACTOR=1. in input file 3.00E E E+00 HRR (kw) 1.50E E E E E E E E E-01 Time (s) 5% Water fraction 10% Water fraction

7 Complex Pyrolysis Model Reaction Rates =, Key parameters: A pre-exponential factor (frequency factor) (s-1) E Activation energy (kj/kmol) N_S Reaction order (-) s Transient material density s,0 Original material density (DENSITY) 3/2/2016 7

8 Complex Pyrolysis Model Arrhenius equation Gas phase reaction Temperature and concentration Rate = f C and T

9 TGA How to get A, E and n? Kinetic properties A simplified hand calculated method E A n Birch TGA 9

10 TGA Method 2 REFERENCE_RATE A = 1E10 E = 1.5E5 N_S = 1 REFERENCE_TEMPERATURE Specify REFERENCE_TEMPERATURE = 371 HEATING_RATE = 10 REFERENCE_RATE = PYROLYSIS_RANGE = 120 PYROLYSIS_RANGE

11 TGA Method 2 = = / missä - Heating rate (K/s) T p Ref temp (K) r p Ref rate (1/s) T Pyrolysis range (K) (0) = 2 (1 )

12 TGA Genetic Algorithm Gene 1, 1, 1 2, 2, 2,nm Individual Generation User specify ranges Fitness e=0.1 z=2 Offspring reproduction Offspring is detemined by the fitness

13 TGA

14 TGA Test your properties using FDS &MATL N_REACTIONS = 1 (N_REACTIONS > 1 reaction numbers) NU_SPEC & SPEC_ID gas products NU_MATL & MATL_ID solid products &SURF ID = 'SHEATH' THICKNESS = TGA_ANALYSIS =.TRUE. TGA_HEATING_RATE = 2.

15 TGA 1-step single reaction: A B + C Multiple reactions: 1-step multi components A B + C D E + F 2-steps A B + D E+F Reaction types 1 component multi reactions A B + C D + E

16 Cone calorimeter 1D Heat transfer

17 Cone calorimeter Cone model in FDS &SURF ID = 'MDF' MATL_ID(1,1:2) = 'Cellulose', Void' MATL_MASS_FRACTION(1,1:2) = , E-05 RGB = 165,42,42 BACKING ='INSULATED' STRETCH_FACTOR=1 EXTERNAL_FLUX=20 CELL_SIZE_FACTOR=0.5 THICKNESS(1) = (different mesh)

18 Flame spread The material begins to decompose when the pyrolysis temperature is reached. The released gases can ignite if in the gas phase there is enough oxygen, which heats the material further and accelerates the breakdown. Predicting challenging flame spread Problem of scales!

19 Flame Spread - resolution effect 2.5 cm 5.0 cm 10 cm

20 Assignment 7 MDF pyrolysis MDF Medium-density fibreboard (MDF) is an engineered wood product made of wood fibres combining with wax and a resin binder, and forming panels by applying high temperature and pressure. Radiata pine ~90% PF resin <10% Paraffin wax ~0.6% Poplar+Cypress ~90% UF resin ~10% 20

21 Assignment 7 MDF pyrolysis MDF pyrolysis New Zealand MDF Chinese MDF q cone = 35, 50, 65 kw/m 2 Sample thickness=18 mm Bulk Density=728 kg/m 3 Flaming Non-fire retardant q panel = 30, 40, 50, 60 kw/m 2 Sample thickness=15 mm Bulk Density=736 kg/m 3 Non-Flaming Non-fire retardant 21

22 Assignment 7 MDF pyrolysis 4 components 1-step parallel reactions Mass fraction Let s assume they generate the same char and char yield=20% of orignial mass 3/2/

23 Assignment 7 MDF pyrolysis Thermal properties 3/2/

24 Task for assignment 7 Task 1 Run FDS TGA at 5 K/min (using both FDS method and given values) and Compare with the experimental data (please plot the mass loss rate curves at the same figure). You can use tga_analysis.fds example case as a starting point. 20 points Task 2 Run FDS cone modelling for Chinese MDF at 30 kw/m2 and Compare with the experimental mass loss rate data (please plot the mass loss rate curves at the same figure). See Section 8.6 of User s guide 30 points Task 3 Run FDS cone modelling for New Zealand MDF at 35 kw/m2 and Compare with the experimental flame heat flux and mass loss rate data (please plot the curves at the same figure) 50 points 3/2/

25 Task for assignment 7 Calculate you own points and submit with the report You may adjust the properties to get a better result but you have to justify you modification in the report. 3/2/

26 Task for assignment 7 What to submit 1. Report 2. Excel file with your fds results (and with the expt data), the compared curves in the same figure and the correlation coefficients 3. FDS input file Please read the slides and the experimental data carefully. There might be some hiding information which I expecting you figure them out yourself. 3/2/