primer “hydrogen deflagrations” - hysafe...turbulent premixed combustion is particularly...

Primer“Hydrogen deflagrations”

Vladimir MolkovHydrogen Safety Engineering and Research Centre

University of Ulster

Joint Summer School on Fuel Cell and Hydrogen Technology21-25 August 2011, Viterbo, Italy

http://hysafer.ulster.ac.uk/

Contributions and support of:• Colleagues from the HySAFER Centre at the

University of Ulster• Partners from the European Network of

Excellence HySafe (currently International Association for Hydrogen Safety), TrainHy-Prof project and other EC-funded projects, and

• The European Commission are gratefully appreciated.

Acknowledgements

OutlineTypes of explosionsDeflagrations and detonationsCharacteristic pressures of hydrogen-air combustionPotential effects of explosions (P-I damage thresholds)Mitigation of deflagrations by venting techniqueContemporary modelling and LES (Large Eddy Simulation) of hydrogen-air deflagrations:

System of governing equationsMulti-phenomena combustion modelValidations

Types of explosionsTerm “explosion” can be misleading as it could refer to different phenomena:o Physical vessel shell rupture due to overpressureo Runaway reactiono High explosiveso Deflagrations (“flammability limits” or

“premixed flame propagation limits”)o Detonations (“detonability limits”)

Reminder:o Deflagration and detonation are propagation of

a combustion zone at a velocity that is respectively less and greater than the speed of sound in the unreacted mixture.

DeflagrationsA deflagration wave is a propagating premixed flame. Deflagration wave in general propagates at subsonic speed. It is an expansion wave, the pressure drops slightly across it. The displacement flow is bounded by compression waves which can eventually steepen to form a precursor shock wave. In confined space pressure build up is practically uniform due to reflections (deflagration can be mitigated by venting). The strength of the precursor shock depends on the flame speed and acceleration. The deflagration front propagates via the diffusion of heat and mass, e.g. free radicals. Flame speed is a function of mixture composition, turbulence level, extent of confinement and obstruction, different flame instabilities, etc.

DetonationsDetonation waves are combustion waves that propagate at supersonic speeds relative to the mixture ahead of it. The classical model of the detonation structure consists of a leading shock front followed by an induction zone and a reaction zone. A compression wave initiates the chemical reaction via adiabatic compression heating across the leading shock front that raises the temperature. The expansion in the reaction zone and in the product behind the front produce the forward thrust necessary to maintain the leading shock front. Reflections at least doubles the pressure. A self-sustained detonation propagates at a unique velocity known as Chapman-Jouguet velocity (products velocity is sonic relative to the wave).

Characteristic pressuresExternal deflagration (in the open atmosphere) of quiescent hydrogen-air mixture: “0”-0.1 bar.Internal deflagration of hydrogen-air mixture in closed vessel: 4-8 bar depending on mixture composition (quiescent hydrogen-air mixture in the range of concentrations 4-7.1% by volume can burn without overpressure when ignited at the top).Vented deflagrations (internal pressure is practically uniform): “0”-(

Potential effects of explosionsBend, break, or displace load-bearing panels, posts, and beams, possibly causing structural collapse.Distort and possibly rupture pressure vessels, pipes, valves, and instrumentation, releasing hazardous (toxic or explosive) materials into the environment.Shock and vibration can break non-structural components, e.g. glass windows, far from incident.Create fragments which can travel long distances, causing facility damage and bodily injury.Start secondary fires due to thermal radiation from fireballs and heat transfer from combustion products.

P-I damage thresholds

Minor damage

Major damage

50-75% demolished

Mitigation of deflagrations by venting

technique

Two peaks structureExample: Dragosavic (1973)

Cooper et al. (1986):P1 - vent opening, venting of unburned gas then burned;P2 - “external explosion” or highly turbulent combustion of unburned mixture pushed out of the vessel;P3 - decrease of flame front area after flame touches the enclosure walls;P4 - pressure waves resulting from the combustion process couple with the acoustic modes of the vessel and set up sustained pressure oscillations (thus satisfying the Rayleigh criterion)

Four peaks structure4 peaks

3 peaks

2 peaks

0.01 0.10 1.00 10.00Turbulent Bradley number, Brt

2

468

2

468

2

468

2

468

0.001

0.010

0.100

1.000

10.000

red

v2.

5

Vent sizing technology (VST)The conservative form (139 tests – different mixtures)Valid in the full range of conditions (NFPA 68 has limits). NFPA 68 limits: 0.1

Comparison of innovative vent sizing technologywith NFPA 68 standard

TestH2,vol. %

Shape V,m3F,m2

Vent Area, F (m2) Reduced pressure, Pred

VSTc %d NFPAe %d Expf VSTc %d NFPAe %d Expf

K-10-15-C 10 Sph 6.85 0.0177 0.0780 342 0.362 1948 0.0177 3.67 126 260.00 15900 1.625

K-10-15-R 10 Sph 6.85 0.0177 0.1070 506 0.448 2435 0.0177 3.67 224 260.00 22807 1.135

K-10–45-C 10 Sph 6.85 0.1590 0.2214 39 0.986 521 0.1590 0.54 79 6.49 2063 0.300

K-10-45-N 10 Sph 6.85 0.1590 0.4843 205 2.212 1292 0.1590 0.54 598 6.49 8340 0.077

K-15-15-C 15 Sph 6.85 0.0177 0.0753 326 0.223 1163 0.0177 5.34 46 260.00 6985 3.670

K-15-25-C 15 Sph 6.85 0.0191 0.1002 104 0.238 384 0.0491 4.20 27 46.90 1321 3.300

K-15-45-N 15 Sph 6.85 0.1590 0.4139 160 0.422 165 0.1590 2.68 113 6.49 417 1.255

K-20-15-C 20 Sph 6.85 0.0177 0.0536 203 0.185 947 0.0177 6.14 22 260.00 5069 5.030

K-20-25-C 20 Sph 6.85 0.0191 0.0819 67 0.196 300 0.0491 5.13 13 46.90 931 4.550

K-20-45-C 20 Sph 6.85 0.1590 0.1643 3 0.222 40 0.1590 3.74 1 6.49 75 3.700

P-1-C [94] 29.6 Cyl 0.95 0.20 0.2132 7 0.110 -45 0.2000 1.35 8 0.45 -64 1.250

P-2-C [94] 29.6 Cyl 0.95 0.30 0.4176 39 0.233 -22 0.3000 0.74 85 0.26 -35 0.400

SRI-30-F 30 Tun 37.4 7.48 11.95 60 1.112 -85 7.48 1.72 33 0.05 -96 1.300

SRI-20-F 20 Tun 37.4 7.48 11.82 58 2.434 -67 7.48 0.78 122 0.05 -85 0.280

SRI-15-F 15 Tun 37.4 7.48 7.48 0 3.127 -58 7.48 0.23 0 0.05 -77 0.220

VST versus NFPA 68

Bartknecht (1993) suggests a mass of less then 10 kg/m2.NFPA 68 standard suggested approximately 12 kg/m2.Cooper (1998) stated that for volumes beyond 100 m3, doors with a mass of less than 20 kg/m2 could be employed with little or no penalty on the predicted reduced pressure.In the UK, values of up to 25 kg/m2 have been acceptable in the past, with some vents being more than 40 kg/m2.The Russian standard SNiP II-90-81 allows the inertia of relief panel of 120 kg/m2!

/V, m3 F, m2 F/Acs Br w, kg/m20.1 0.04 0.20 31 4.5 2.7 < 0.3110 1.76 0.38 59 8.6 5.2 < 16

100 11.62 0.54 84 12.3 7.4 < 1131000 77.70 0.78 122 17.7 10.6 < 782

Vent cover inertia

Le Chatelier-Broun principle

The Le Chatelier-Broun principle: any change in status quo prompts an opposing reaction in the responding system. This principle works for vented deflagration phenomenon: gas combustion dynamics in vented vessel responds to external changes in explosion conditions in such a way as to weaken the effect of external influence.Below is an example based on use of the theoretical formula:

It follows from the formula that 10 increase of vent area F willlead to 100 decrease of overpressure m. However, experiments in 10 m3 volume vessel showed that tenfoldincrease in vent area is accompanied by twofold increase ofturbulence factor . It results in “effective” vent area increase of only 10/2=5 times. Physical explanation of this observation: the increase of vent area increases the flame turbulence.

2)/( FSum

Contemporary modellingand LES of deflagrations

Introduction The Ulster’s Large Eddy Simulation (LES) deflagration model

• Multi-phenomena turbulent burning velocity sub-model

Validations:3a: Open atmosphere deflagrations3b: Closed vessel deflagrations 3c: Vented deflagrations3d: Deflagrations in 78.5 m length tunnel3e: Lean and non-uniform H2-air mixtures in a 5.7 m cylinder

Outline

19

Bilger R.W., Pope S.B., Bray K.N.C., Driscoll J.F. (2005) stated that in spite of the progress in combustion science in last 50 years, our understanding of turbulent combustion remains far from complete, premixed turbulent flames seem to be dependent on a much wider range of factors, and predictive capabilities are not so advanced.Computational Fluid Dynamics (CFD) is a widely used contemporary tool for solving complex scientific and engineering problems.

Introduction (1/8)

20

Turbulent premixed combustion is particularly difficult to describe using the large eddy simulation (LES) technique (Knudsen E., Pitsch H., 2008): neither laminar flameletstructure nor fine details of turbulent flame brush structure can be resolved at problem scales of tens and hundreds of meters.Nevertheless, LES models must be capable of describing the dynamics and consequences of large-scale premixed combustion at conditions of completely unresolved flame structures. This is usually accomplished through the implementation of a sub-grid scale (SGS) model for the turbulent burning velocity, which explicitly appears in the equations of motion.

Introduction (2/8)

21

LES resolves directly large scale energy contained eddies and provides good estimations of highly nonisotropic turbulent flows and large-scale flame-flowinteraction at the resolved level (Hawkes, Cant, 2001; Poinsot, Veynante, 2001)For “standard” LES it is recommended that 80% of eddies are resolved to be “in depth” in the inertial range (S. Pope). The term “VLES” (Very LES) may be used otherwise. Such approaches requires robust turbulent sub-grid scale combustion model (Pope, 2004).For reacting flows the success depends on the quality of SGS modelling of the turbulent burning velocity.

Introduction (3/8)

22

Large Eddy Simulations (LES)Very Large Eddy Simulations (VLES)Following argument by S. Pope: LES was developed for non-reacting flows. Combustion models both for RANS and LES are similar.The first group (I) of turbulent burning velocity models assumes dependence on the ratio of r.m.s.velocity to laminar burning velocity, u’/Su, only (these models are not able to reproduce even acceleration of unconfined flames).

Introduction (4/8)

Ts

ds

,ts

DNS

RANS

LES23

The second group (II) of models introduces an additionaldependence of turbulent burning velocity on turbulence scale(s), which are difficult to interpret and which are calibrated by small-scale experiments thus limiting their extrapolation to large-scale problems

The last group (III) of fractals models introduces dependence of the turbulent burning velocity on the transient outer cut-off (integral scale) and the inner cut-off, e.g. laminar flameletthickness, of the problem. Meaningful comparisons between the first and the last groups are not possible (North, Santavicca, 1990).

Introduction (5/8)

3 4

51 2

'b b

btT

L L

ls ub b Les s

24

Introduction (6/8)Coherent deflagrations (1/3)

Shell SOLVEX:V=547 m3;10.5% methane-air mixture;Initially open vent;Back-wall ignition.

25

Time, ms

Pres

sure

, Pa

0 200 400 600 800 1000 1200-4000-3000-2000-1000

0100020003000400050006000

Simulated internal pressure dynamicsSimulated external pressure dynamics

H’

G’

F’E’D’C’B’A’

Ulster’s simulation

Shell’s experiment

ext =1 2

External explosion (in 100 ms):


26

Ulster LES model

Shell 4

Shell 3


27

The Ulster’s LES deflagration model

128

J. Phys. D: Appl. Phys. 39 (2006) 4366–4376

• Conservation of mass

• Conservation of momentum (Navier-Stokes equations)

• Conservation of energy

Governing equations (1/3)

0~jj

uxt

iijk

k

i

j

j

ieff

jii j

j

i gxu

xu

xu

xxpuu

xtu ~

32~~~~~

pEux

Et jj

~~~

ccijk

k

i

j

j

ieffi

m j

m

eff

effm

jeff

peff

j

HSxu

xu

xuu

xY

Sch

xTc

x

~

32~~~

~~~

Pr

29

• Renormalization (RNG) SGS turbulence model

• Dilution of initial hydrogen-air mixture by atmospheric air (open atmosphere, vented deflagrations)

31

3

2

1001 effseff H

ijijCVs SSV~~2157.0 231

effeffeffeff

effeff ScNNN

NN

;Pr;3929.23929.21

3929.113929.11 3679.06321.0

i

j

j

iij x

uxu

S21

cHa

a

j

a

eff

eff

jaj

ja SYY

YxY

ScxYu

xY

t2

~~~~~~~

7.0Pr 7.0Sc


30

• Premixed flame front propagation (the progress variable)

• The gradient method for the source term

• Chemistry is in laminar flamelet burning velocity (T, p, )

• Next section explains a multi-phenomena turbulent burning velocity sub-model of the Ulster’s LES deflagration model

~)(cgradSS tuc

c

jeff

eff

jj

j

Sxc

Scxcu

xc

t

~~~~

umnmiui

ni

muiiuiuiu ppSppTTpTSpTS

////),,(),,(


31

1)(~

dxcgrad

Multi-phenomena turbulent burning velocity sub-model

232

Phenomena includedIn addition to dependence of laminar burning velocity on mixture composition, pressure, and temperature the following four phenomena affecting turbulent burning velocity are currently included into the Ulster’s LES model:

(I) Flow turbulence (all scales),(II) Turbulence generated by flame front itself (SGS),(III) Preferential diffusion effects (leading point concept)

for lean hydrogen-air mixtures (SGS),(IV) Fractals structure of turbulent flame surface (all

scales)

33

(I) Flow turbulenceThe renormalization group (RNG) theory (Yakhot and Orszag, 1986) is applied to calculate both turbulent burning velocity and turbulent viscosity. The RNG method is favoured for its ability to model flows in both limits - laminar and turbulent. The original Yakhot’s equation for turbulent flame propagation velocity is a basis of the model (no empirical coefficients!)

The criticism of the Yakhot’s formula could be bounced back to sceptics on inappropriate use of the equation. The modified Yakhot’s equations used in the Ulster LES model

2

expt

ut SuSS

2

expt

SGStt S

uSSuS

SGStS

34

(II) Turbulence generated by flame front itself (1/2)

The recognition that the turbulent flame itself generates additional turbulence first came in 1951 (Karlovitz et al.).The unburned mixture passes through the flame front with a laminar burning velocity Su. However, the combustion products leave the flame front with velocity Ei.Su, where Ei iscombustion products expansion coefficient (7-8 for fast burning hydrogen-air mixtures). Thus, the flame front constitutes a flow source that introduces a velocity into the gas flow of the magnitude (Ei-1).Su. In turbulent flame brush the flamelets are subject to fluctuating motions, and hence the orientation of this flame-induced velocity fluctuates also. An upper limit of flame-generated turbulence(high turbulence) can be estimated as

3)1( ui SEu

35

(II) Turbulence generated by flame front itself (2/2)

Consequently, the upper limit for a flame wrinkling factor due to the turbulence generated by flame front itself is

Gostintsev et al. (1988): a critical radius for transition from laminar to fully developed turbulent flame for near stoichiometric hydrogen-air mixtures is R*=1-1.2 m. The following formula is suggested for transient value of flame wrinkling factor due to the self-induced flame turbulence

where R is distance from the ignition source, and

(III) Preferential diffusion (1/3)

Turbulent flame is an aggregate of strained flamelets of different curvature. For particular mixture composition there is a curvature radius with maximum burning rate. Thus, flamelets of such curvature will lead propagation of the turbulent flame. The correction factor to laminar burning velocity associated with this mechanism (subscript “lp”stands for “leading point”), is adopted from Zimont and Lipatnikov (1995), who used the formulation by Kuznetsov and Sabelnikov (1990) based on former Zeldovich’s idea. In the multi-phenomena turbulent burning velocity model it is assumed that for initially quiescent mixture the preferential-diffusive instability develops linearly with radius and reaches maximum at half of critical radius R* andremains constant after that.

37

(III) Preferential diffusion (2/3)Kuznetsov and Sabelnikov (1990): theturbulent flame speed is controlled by the burning velocity of leading point flamelets, where the mixture composition is locally altered due to different diffusivity of fuel and oxidiser.They derived the model for a local change in the mixture composition within the leading point combustion zone as follows:

If ,1lpst

stlp Cd

ddC 110

,1lp dCCdC

stst

stlp

00

0

11If 1

5.0

f

ox

DDd

38

(III) Preferential diffusion (3/3)

0.5

1.0

1.5

2.0

2.5

3.0

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Hydrogen mole fraction

X_lp

Preferential diffusion correction to SGS turbulent burning velocity (Zimont and Lipatnikov (1995) based on tests by Karpov and Severin).

39

(IV) Fractals (1/2)The fractal theory was developed for description of highly contorted and roughened curves and surfaces. The nature of combustion in the regime for the Peclet number(flame radius/flame thickness) above the critical is referred as fractal-like flame wrinkling and is responsible for a further increase of the turbulent burning velocity (Bradley, 1999).According to fractals the flame surface area of outward propagating turbulent flame will grow not as R2 that is valid for laminar flame, but faster as R2.RD-2, where D is the fractal dimension (experimental data 2.11-2.35). The empirical parameterization of the fractal dimension as a function of (u’/Su) (North and Santavicca, 1990) is applied

1'35.2

1'05.2

uSSuD

uu

40

(IV) Fractals (2/2)The integral scale of the problem R, e.g. flame radius, is the outer cut-off. The inner cut-off is chosen currently as a laminar flame front thickness . The effect of changing temperature of unburned mixture and explosion pressure on the inner cut-off was calculated assuming , where is kinematic viscosity. To exclude a stage of quasi-laminar/transitional flame propagation after ignition up to the critical radius R*, when fractals theory can be hardly applied, it can be shown that an additional wrinkling factor due to the fractals nature of the turbulent premixed flame surface to be applied after R* is

2*

*

DR

f RR

uL S

41

Final equation for StThe multi-phenomena turbulent burning velocity model for LES of premixed combustion is being developed during the last decade at the University of Ulster. The final equation for turbulent burning velocity currently casts as

In addition to the dependence of laminar burning velocity of pressure, temperature, and mixture composition, the model for the first time accounts, in an aggregate manner, for four interrelated SGS mechanisms of increase of flame front area:

- flow turbulence- turbulence generated by flame front itself, - preferential diffusion effects in a turbulent brush, and - fractal growth of turbulent flame front surface area

2

exp][t

flpKut Su

SS

42

The LES deflagration model validations

33a: Open atmosphere deflagrations (Fraunhofer ICT)3b: Closed vessel deflagrations 3c: Vented deflagrations3d: Deflagrations in 78.5 m length tunnel3e: Lean and non-uniform H2-air mixtures in a 5.7 m cylinder

43

Open atmosphere deflagrations (Fraunhofer ICT)

3a44

20 m10 m3.06 mTest No. Db, m V, m3 C, % vol. Ti, K pi, kPa Eign, J , m/s , m/s , m/s

GHT 26 3.06 7.5 29.2 281 99.06 1000 2.32 2.55 43

GHT 11 10.00 262 31.0 281 100.66 314 2.50 3.32 60

GHT 34* 20.00 2094 29.7 283 98.93 150 2.39 4.84 84

* - Experiments with wire net over the hemispherical balloon.

Fh-ICT experiments: Schneider H., Pförtner H. PNP-Sichcrheitssofortprogramm, Prozebgasfreisetzung-Explosion in der gasfabrik und auswirkungen von Druckwellen auf das Containment, Dezember, 1983.

expuiS

expmax

expmaxw

Open atmosphere (1/4)

45

20 m

10 m


46


47

Open atmosphere (4/4)Hemisphere 10 m diameter (Fraunhofer ICT)

0123456789

10

0.00 0.05 0.10 0.15 0.20 0.25

Time (s)

Flam

e ra

dius

(m)

Experiment

Model v2.2b, D=2.20

Model v2.2b, D=2.33

-8

-6

-4

-2

0

2

4

6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35Time, s

Ove

rpre

ssur

e, k

Pa

6.85 mExperimentModel v2.2b, D=2.33Model v2.2b, D=2.2

-8

-6

-4

-2

0

2

4

6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35Time, s

Ove

rpre

ssur

e, k

Pa


-8

-6

-4

-2

0

2

4

6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35Time, s

Ove

rpre

ssur

e, k

Pa


48

Closed vessel deflagrations

3b49

Closed sphereKumar et al. (1983):V=6.37 m3, D=2.3 m, T=373 K, p=97 kPa

0

100

200

300

400

500

600

700

0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070Time (s)

Pres

sure

(kPa

)

Experiment

Model v1.1

Model v1.2b

Model v3.1

50

Whitehouse et al. (1996):L=5.7 m; D=1.5 m (V=10.1 m3), uniform 12–20% mixture

Closed vessel: uniform

51

Closed vessel: gradientWhitehouse et al. (1996): L=5.7 m; D=1.5 m (V=10.1 m3), uniform (12.8%) vs non-uniform (average 12.6%, 2.5-27%)( %) (

52

LES of vented deflagrations

3c53

Vented deflagration (1/3)

Simulations:Sui=1.73 m/s, m0=1.7, =0.57

=0.5, R*=1.2 m, K=1.7, lp=1.28xCV 0.045 m, total CV number 159,000

Experiment: Pasman H.J., Groothuisen Th.M. and Gooijer P.H. (1974) Design of Pressure Relief Vents, in “Loss Prevention and Safety Promotion in the Process Industries”, Ed. Buschman C.H., Elsevier, New-York, pp.185-189.Cylindrical vessel: L D=1.50 0.97 m, V=0.95 m3

Vents: 0.3 m2 ( =0.62 m) and 0.2 m2 ( =0.5 m)Vent relief overpressure: 13.5 kPa ( =0.62 m), 7.5 kPa ( =0.5 m)CH2=29.6% (vol.), central ignition, quiescent mixture, p0=101.8 kPa, Tu0=281 K.

54

05

101520253035404550

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040

Time (s)

Ove

rpre

ssur

e (k

Pa) Experiment

Simulation

Vent =0.62 m Vent =0.50 m

0

20

40

60

80

100

120

140

160

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040

Time (s)O

verp

ress

ure

(kPa

) ExperimentSimulations


55

Simulation, vent =0.50 m


56

LES of deflagrations in 78.5 m length tunnel

3d57

SRI Tunnel (1/5 scale), Groethe et al. (2005): 78.5 m length Horseshoe cross section: 3.74 m²Hydrogen-air mixtures: 30% and 20% by volumeVehicle size: LxHxW = 0.94x0.362x0.343 m (BR = 0.05) Separating distance between vehicles: 0.940 m

Tunnel 78.5 m length (1/6)

58

39.25 m (half of the tunnel)

H2-air mixture

Ignition at the centre of the tunnel


59


60


61

R = 1.00 m

-80

-60

-40

-20

0

20

40

60

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Time (s)

Ove

rpre

ssur

e (k

Pa)

ExperimentModel v2.2aModel v3.1

R = 3.61 m

-80

-60

-40

-20

0

20

40

60

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Time (s)

Ove

rpre

ssur

e (k

Pa)


R = 10.61 m

-80

-60

-40

-20

0

20

40

60

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Time (s)

Ove

rpre

ssur

e (k

Pa)


R = 30.40 m

-80

-60

-40

-20

0

20

40

60

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Time (s)

Ove

rpre

ssur

e (k

Pa)

Experiment

Model v2.2a

Model v3.1

Tunnel 78.5 m length (5/6)20% hydrogen-air mixtures of 37.4 m3 volume (10 m long cloud)

62

30% hydrogen-air mixture deflagration, with obstaclesR=1.00 m

-100

-50

0

50

100

150

200

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Time (s)

Ove

rpre

ssur

e (k

Pa) Experiment

Simulation

R=10.61 m

-100

-50

0

50

100

150

200

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Time (s)

Ove

rpre

ssur

e (k

Pa) Experiment

Simulation

R=30.4 m

-50

0

50

100

150

200

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Time (s)

Ove

rpre

ssur

e (k

Pa) Experiment

Simulation

R=3.61 m

-100

-50

0

50

100

150

200

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Time (s)

Ove

rpre

ssur

e (k

Pa) Experiment

Simulation


63

Lean uniform and non-uniform deflagrations in a 5.7 m height

cylinder(Nuclear Engineering and Design, 1996, 66:453-462)

3e64

Calculation domain

CV= 0.08 m; 157,352 CVs in total;

65

Lean hydrogen-air mixtures

66

Effect of preferential diffusion

12.8% H2-air20% H2-air

67

12.8% uniform mixture

68

Concentration gradient effect

Uniform 12.8% H2-air

Gradient 12.6% H2-air (2.5-27%)

69

The only unknown parameter

For unconfined and semi-confined hydrogen-airdeflagrations in the range 20-30% by volume of hydrogen:

For lean hydrogen-air mixtures in the range 12-20% by volume:

For non-uniform hydrogen-air mixture (average 12.6 % by volume):

5.0

1

7.0

70

MSc in Hydrogen Safety Engineering (distance learning course):http://campusone.ulster.ac.uk/potential/postgraduate.php?ppid=24MS i H d S f

primer “hydrogen deflagrations” - hysafe...turbulent premixed combustion is particularly...

Documents