Pressure limit of hydrogen spontaneous ignition in a T-shaped channel

Transcription

1 4 th International Conference on Hydrogen Safety, September 2011, San Francisco, USA Pressre limit of hydrogen spontaneos ignition in a T-shaped channel Maim Bragin, Dmitriy Makarov, Vladimir Molkov Hydrogen Safety Engineering and Research (HySAFER) Centre, University of Ulster

2 Backgrond Aim and obectives Eperiment in T-shape channel (Golb et al., 2010) LES EDC model Modelling of membrane opening Instant verss finite membrane opening Simlation reslts Otline Dynamics of spontaneos ignition at different storage pressre Conclsions

3 Backgrond Pressre relief device (PRD) activation Sdden release of hydrogen into air What is the lower pressre limit for spontaneos ignition in T-shape channel (PRD mock-p)?

4 Aim and obectives Aim: Develop contemporary model for predictive simlation of the phenomenon of hydrogen spontaneos ignition dring sdden release from pressre relief devices (to be applied as a tool for hydrogen safety engineering) Obectives: Develop Large Eddy Simlation (LES) model based on the Eddy Dissipation Concept (EDC), fll chemistry, and modelling of a brst disk opening in a finite time Validate the LES EDC model and simlations against eperimental data by Golb et al. (2010) on spontaneos ignition in T-shape channel (mock-p PRD) Understand dynamics of the ignition process and eplain scattering in reported eperimental data (Golb et al., 2010) Establish the lower pressre limit for spontaneos ignition in T-shape channel

5 Eperiment (Golb et al., 2010) Brst disk rptre at storage pressres from 13.5 to 29 bar. Reported: no ignition at 13.5 bar, and spontaneos ignition at 29 bar (private commnication ignition at 24.3 bar) Brst disk ID 4 ID 16 ID 10 ID High-pressre section (hydrogen) PRD (air)

6 Comptational domain High pressre tbes PRD Eternal domain Brst disk

7 LES eqations ( ) 0 = t ρ ρ ( ) i i k k i i i i i g p t ρ δ μ ρ ρ = 3 2 ( ) ( ) ( )= p E E t ρ ρ m m m p Y Sc h T c Pr [ μ μ ( ) ( ) m m m H R Y Sc Y Y t = μ ρ ρ Continity eqation: Momentm conservation eqation: Energy conservation eqation: Species conservation eqation: m C m i k k i i i H R ] 3 2 δ μ

8 RNG trblence model The ective viscosity in RNG SGS model is calclated as μ 2 μs μ = μ 1 H μ , where μ = ( 0.157VCV ) 2Si Si In highly trblent flows, μ μ s and the RNG model redces to Smagorinsky model in laminar flow regions the argment of Heaviside fnction becomes negative and the model recovers moleclar viscosity, = μ. The ective Prandtl and Schmidt nmbers are calclated following the RNG theory by Yakhot prely from the theoretical eqation 1 1 N N μ N N S = s i = ρ μ μ 1 2 i i

9 EDC combstion model 1/2 Eddy Dissipation Concept (EDC) gives an epression for a combstion rate based on an assmption that chemical reactions occr in so-called fine strctres of Kolmogorov s scale, where the dissipation of trblence energy takes place. In EDC model a sorce term in species ( ) 2 transport eqation is modelled as: ρ ξ [ ] ( R ) m = Ym Y 3 m τ 1 ξ R m is a net rate of prodction of specie m by chemical reactions, * ξ ( ) is the length fraction of the fine scale trblent strctres where the reaction occrs, Y m is the fine scale species mass fraction (specie m) after reacting over the time, τ Y m is a species mass fraction for specie m in the srronding fine scales state.

10 The length fraction of fine strctres: ξ = η / SGS 1 3 where = μ ρ L ) and L SGS = 0.157V SGS t EDC combstion model 2/2 /( SGS 3 μ SGS and the Kolmogorov s velocity η = ρ LSGS Characteristic sb-grid eddy and Kolmogorov timescales are: 1 2 τ SGS = L SGS / SGS and τ μ L SGS = η 3 ρ SGS * The volme fraction of the fine scales is calclated as ξ 3 and species are assmed to react in the fine strctres over a time scale τ = τ η. It is assmes that all the fine scales in the cell are perfectly * stirred reactors with a residence time τ 1 4

11 Chemistry mechanism Mechanism for H2 combstion (with NO), 13 species and 37 reactions Units are cm3, mol, s, KJ and K HO2=OHO 2.E H2O=OHH 1.8E H2OO=OHOH 5.9E H2OH=H2OH 1.17E HO2M=HO2M 2.3E H2/1./ H2O/6.5/ O2/0.4/ N2/0.4/ HHO2=OHOH 1.5E HHO2=H2O2 2.5E OHHO2=H2OO2 2.E HHM=H2M 1.8E H2/1./ H2O/6.5/ O2/0.4/ N2/0.4/ HOHM=H2OM 2.2E H2/1./ H2O/6.5/ O2/0.4/ N2/0.4/ HO2HO2=H2O2O2 2.E H2O2M=OHOHM 1.3E H2O2OH=H2OHO2 1.E OHO2=OHO2 2.E HHO2=OH2O 5.E HOM=OHM 6.2E OOM=O2M 6.17E H2O2H=H2OOH 1.E H2O2H=HO2H2 4.79E OOHM=HO2M 1.E H2O2=OHOH 1.7E ON2=NNO 1.82E ONO=NO2 3.8E HNO=NOH 2.63E NOM=NOM 3.98E N2M=NNM 3.72E N2OO=NONO 6.92E N2OO=N2O2 1.E N2ON=N2NO 1.E NHO2=NOOH 1.E N2OH=N2OH 7.6E HNOO=NOOH 5.01E HNOOH=NOH2O 1.26E NOHO2=HNOO2 2.E HNOHO2=NOH2O2 3.16E HNOH=NOH2 1.26E HNOM=HNOM 1.78E GUTHEIL, E., BALAKRISHNAN, G. & WILLIAMS, F. A. (1993) Strctre and etinction of hydrogen-air diffsion flames. IN PETERS, N. & ROGG, B. (Eds.) Redced kinetic mechanisms for applications in combstion systems. New York, Springer-Verlag

12 Brst disk opening sections Brst disk opening process was approimated by a 10 step process. Sections were open from 1 to 10 at times calclated according to the table in the net slide.

13 Brst disk opening time Following Spence & Woods (1964), the following formla was sed to obtain the rptre time of a brst disk: t = ρbd k p 1 2 where ρ the density of the diaphragm material (annealed copper), b and d are the thickness and the diameter of the diaphragm, k constant, 0.92 p driving pressre Opening times of sections for each of the simlations are listed below: Section Opening time, μs [1.35 MPa case] Opening time, μs [1.65 MPa case] Opening time, μs [2.43 MPa case] Opening time, μs [2.9 MPa case]

14 Instant vs finite opening time

15 Simlation reslts

16 P=29 bar Ignition initiated in the radial vent channel and etingished. Combstion is reinitiated in a nmber of spots otside the PRD. Concentration of hydrogen in these spots st before the ignition is in the range 29-36% by vol.

17 P=24.3 bar Ignition is initiated in the radial channel (closer to the pstream wall second shock reflection) similar to 29 bar case Reignition otside is not observed. Process took 10μs and was eperimentally registered ( ignition in private commnication)

18 P=16.5 bar Temperatre Ignition spot is located in the aial channel (not in a symmetry plane). The combstion propagates pstream (ntil oygen is consmed)! Iso-srfaces are: Ble 550 K, Green 1500 K, Red 2400 K

19 P=16.5 bar OH mole fraction Ignition is confirmed by a hydroyl mole fraction distribtion. Light sensor in eperiments was located otside and cold not have registered ignition. Iso-srfaces are: Ble , Green 0.002, Red 0.02

20 P=13.5 bar no ignition Hydroyl mole fraction is (not shown). Note: temperatre scale is different in this pictre.

21 Conclsions The LES model based on EDC with detailed kinetics and inertial brst disk was sccessflly applied to reprodce and eplain eperimental observations in T-shape channel (PRD mock-p). The lower pressre limit for spontaneos ignition in a T- shaped PRD is established: there is no ignition at storage pressre 13.5 bar; there is ignition followed by selfetinction at pressres 16.5 and 24.3 bar; and there is sstainable ignition (reignition otside the channel) for storage pressre 29 bar. The ignition is located in the are of the second reflection of initial shock and where the concentration of hydrogen in air is in the range 29-36% vol. The model can be sed as a contemporary tool for design of innovative pressre relief devices.

22 MSc in Hydrogen Safety Engineering (distance learning corse): 22