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, sgiannissi@ipta.demokritos.gr, venets@ipta.demokritos.gr 2School of Chemical Engineering, National Technical University of Athens, Heroon Polytechniou 9, 15780, Athens, Greece, n.markatos@ntua.gr ICHS2015 International Conference on Hydrogen Safety 19-21, 2015 Yokohama, Japan

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. 17589–17598. 21 Oct. 2015

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 0.00455 19 37 451.05 1 IF3004 0.00802 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. 21 Oct. 2015

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 21 Oct. 2015

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

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. 21 Oct. 2015

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

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

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 21 Oct. 2015

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 0.012 m behind the nozzle Refinement near the source region. Small expansion ratios (1.05-1.12) 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”, http://www.support-cfd.eu/ 21 Oct. 2015

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 1.05-1.12) 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 1.05-1.12 167,552 136,320 #2 2 243,648 196,080 #3 1.04-1.09 349,596 255,255 21 Oct. 2015

Sensitivity studies Results from the grid independency study 21 Oct. 2015

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 5.6-7.5% at the furthest sensors for Ewan and Moodie approach overprediction underprediction underprediction 21 Oct. 2015

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 21 Oct. 2015

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 21 Oct. 2015

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. 21 Oct. 2015

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 21 Oct. 2015

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-325386). The authors would also like to thank Mikhail Kuznetsov for the useful discussion and the information that were provided regarding the experiments.