1. MODELING OF CRYOGENIC HYDROGEN JETS
S.G. Giannissi1,2, A.G. Venetsanos1, N. Markatos2
1Environmental Research Laboratory, National Centre for Scientific Research Demokritos, Aghia Paraskevi, Athens, 15310, Greece,
2School of Chemical Engineering, National Technical University of Athens, Heroon Polytechniou 9, 15780, Athens, Greece,
ICHS2015 International Conference on Hydrogen Safety 19-21, 2015 Yokohama, Japan

2. Experimental description (1/2)
Cryogenic hydrogen jet releases conducted by KIT1
26 experiments performed to investigate hydrogen distribution and 11 experiments for hydrogen combustion
Hydrogen is released horizontally in large chamber of hydrogen test site HYKA at KIT (8 x 5.5 x 3.4 m). The chamber is large enough compared to jet region, so it does not affect the jet.
The nozzle is 1 m above ground.
Supercritical state all
Image of an un-ignited cryogenic hydrogen jet1
1 Friedrich, A., Breitung, W., Stern, G. , Veser, A., Kuznetsov, M., Fast, G., Oechsler, B., Kotchourko, N., Jordan, T., Travis, J. R., Xiao, J., Schwall, M. and Rottenecker, M. (2012). Ignition and heat radiation of cryogenic hydrogen jets, Int. J. Hydrogen Energy, 37, No. 22, pp –17598.
21 Oct. 2015

3. Experimental description (2/2)
The main characteristics for the simulated test cases
Exp.
Mass flow (kg/s)
Reservoir Pressure (bar)
Reservoir temperature (K)
Velocity at nozzle (m/s) *
D nozzle (mm)
IF3000 19 37
451.05 1
IF3004 29 36
718.12
Velocity at the nozzle has been given by KIT employing the homogeneous non-equilibrium two-phase critical flow model.
An isentropic path is followed from the reservoir conditions to several pairs of pressure and temperature. The pair at which the maximum (critical) mass flux is estimated corresponds to the conditions at the nozzle. This critical flux should be equal to the measured one.
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4. Modeling approach Governing equations and numerical details
ADREA-HF CFD code is employed
Mass conservation equation
Momentum conservation equations
Enthalpy conservation equation
Hydrogen mass fraction conservation equation
Peng-Robinson equation of state (EOS) is used.
k-epsilon turbulence model with extra buoyancy terms
1st order fully implicit scheme for time integration, QUICK (3rd order) numerical scheme for the convective terms, central differences (2nd order) numerical scheme for diffusion terms,
CFL =10 for time step control
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5. Modeling approach Source modeling
Modeling under-expanded jets: Complex shock structure occurs downwind the nozzle. High computational cost to resolve the conservation equations at that region.
Notional nozzle approaches
Estimate the conditions (P,T,u,A) at the notional nozzle (level 3) employing an available approach and impsose them as hydrogen inlet boundary. The nozzle conditions (level 2) are necessary. Isentropic process from the reservoir conditions (level 1) is assumed.
21 Oct. 2015

6. Modeling approach Source modeling
Estimate the nozzle conditions
known parameters
ρn=12.84 for IF3000
ρn=14.22 IF3004
Estimate pair of P,T following an isentropic path until the density at nozzle is found. The T-S diagram is used.
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7. Modeling approach Source modeling
T-S diagram2
Two phase conditions at the nozzle
Tn=30.5 K for IF3000
Tn=28 K for IF3004
Pressure is the saturation pressure at the nozzle temperature
IF3000
IF3004
2 G. Gstrein and M. Klell (2004). Stoffwerte von Wasserstoff [Properties of Hydrogen], Institute for Internal Combustion Engines and, Thermodynamics, Graz University of Technology
21 Oct. 2015

8. Modeling approach Source modeling
Notional nozzle approach
Conditions at the notional nozzle (level 3) are calculated using two approaches:
Ewan and Moodie3
Mass balance from level 2 to level 3
Temperature at level 3 equal to nozzle temperature
Pressure at level 3 equal to atmospheric
Vapor phase only at level 3
Sonic velocity at level 3
Notional area by mass flow rate
Modified Ewan and Moodie * (based on Birch 874)
Mass balance from level 2 to level 3
Temperature at level 3 equal to nozzle temperature
Pressure at level 3 equal to atmospheric
Vapor phase only at level 4
Velocity calculated by performing momentum balance from level 2 to level 3
Notional area by mass flow rate
* introduced here
3B.C.R. Ewan and K. Moodie(1986). Structure and Velocity Measurements in Underexpanded Jets,” Combust. Sci. Technol., 45, No. 5–6, pp. 275–288
4 A.D. Birch, D.J. Hughes, and F. Swaffield (1987). Velocity decay of high pressure jets, Combust. Sci. Technol., 45, pp. 161–171
21 Oct. 2015

9. Modeling approach Source modeling
Summary of the conditions at the hydrogen inlet boundary
Exp.
Pressure (bar)
Temperature (K)
Velocity (m/s)
Notional nozzle (mm)-square side
Ewan and Moodie
Modified Ewan and Moodie
IF3000
1.01
30.5
419.9
583.9
3.6 3
IF3004
 28 28
402.1
764.4
4.7
3.4
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10. Modeling approach Computational domain and grid design
Computational domain and grid, boundary conditions etc. are designed based on the Best Practices in numerical simulations5 developing within the SUSANA project6
Domain large enough (4.012 x 0.5 x 2 m) and appropriate open boundary conditions (constant pressure)
West domain is set m behind the nozzle
Refinement near the source region. Small expansion ratios ( ) downwind the release, especially across the release direction and on the z-direction
Symmetry plane along y-axis
Source is modeled as a solid surface (square) with area equal to the one calculated using the notional approaches and conditions (P,T,u) the ones estimating by the notional nozzle approaches. Blocked cells behind the source surface
5 Venetsanos, A.G, Tolias, I.C., Giannissi, S.G., Coldrick, S., Ren, K., Kotchourko, A., Makarov, D., Chernyavsky, B., Molkov, V., D3.1 Guide to best
practices in numerical simulations, Rep. SUSANA Project
6 “SUSANA project webpage”,
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11. Sensitivity studies The main characteristics of the tested grids
According to Best Practices in numerical simulations grid independency study sensitivity study was performed
Grid independency study (with Ewan and Moodie approach)
3 grids were examined
1. One cell along the source diameter (expansion ratios )
2. Two cells along the source diameter
3. One cell along the source diameter, but smaller expansion ratios
The main characteristics of the tested grids
Grid
Cells along diameter
Expansion ratios
Grid size
IF3000
IF3004 #1 1
167,552
136,320 #2 2
243,648
196,080 #3
349,596
255,255
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12. Sensitivity studies Results from the grid independency study
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13. Results IF3000 overprediction underprediction underprediction
Statistical Measure
Ideal value
Ewan and Moodie
Modified Ewan and Moodie FB
-0.068
0.067
NMSE
0.08
0.06 MG 1
1.015
1.178 VG
1.033
1.067
Relative error less than 30% at most of the sensors using both approaches. ~33% at the closest to the nozzle sensors and less from % at the furthest sensors for Ewan and Moodie approach
overprediction
underprediction
underprediction
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14. Results IF3004 underprediction underprediction Statistical Measure
Ideal value
Ewan and Moodie
Modified Ewan and Moodie FB
0.230
0.50
NMSE
0.097
0.37 MG 1
1.250
1.756 VG
1.09
1.42
Maximum relative error ~38%, minimum error ~3% using the Ewan and Moodie approach
Maximum relative error ~55%, minimum error ~27% using the modified Ewan and Moodie approach
underprediction
underprediction
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15. Conclusions (1/2)
CFD modeling of cryogenic high pressure hydrogen releases
Two tests (IF3000 and IF3004) from the KIT experimental series were simulated
The nozzle conditions were estimated following an isentropic path using the T-S diagram of hydrogen
Notional nozzle approaches were employed to model the under-expanded jet
Ewan and Moodie approach
A modified Ewan and Moodie which is introduced in the present study
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16. Conclusions (2/2) For the IF3000 test For the IF3004 test
Overprediction near the nozzle using both approaches. However, modified Ewan and Moodie approach performs better near the nozzle (relative error 32% and 19% for Ewan and Moodie and modified Ewan and Moodie, respectively), while Ewan and Moodie approach performs better further downwind the nozzle (less than 8% error compared to about 21% with the modified Ewan and Moodie)
Statistical indicators (MG, VG) showed an overall underprediction using both approaches
For the IF3004 test
Using both approaches the predictions tend to under-predict the concentrations at all distances. Ewan and Moodie performs better with relative error ranged between 3-38%
Comparing the two test cases, the prediction of the IF3000 experiment (lower mass flux) is closer to the experiment than the prediction of the IF3004 experiment.
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17. Future work
Perform the isentropic process (two phase chocked flow model using Peng-Robinson EOS) from the reservoir conditions to the nozzle conditions to estimate the nozzle conditions (P,T,u) without using the T-S diagram.
Perform an energy balance from the nozzle to the notional nozzle to obtain the temperature at the notional nozzle
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18. Thank you very much for your attention
Any Questions?
The authors would like to thank the Fuel Cell and Hydrogen Joint Undertaking for the co-funding of the SUSANA project (Grant-Agreement FCH-JU ).
The authors would also like to thank Mikhail Kuznetsov for the useful discussion and the information that were provided regarding the experiments.