CFD MODELING OF LH2 DISPERSION USING THE ADREA-HF CODE

1. CFD MODELING OF LH2 DISPERSION USING THE ADREA-HF CODE Giannissi, S.G.1,2, Venetsanos, A.G.1, Bartzis3, J.G., Markatos2, N., Willoughby, D.B.4 and Royle, M.4 1Environmental Research Laboratory, National Centre for Scientific Research Demokritos, 15310 Aghia Paraskevi, Attikis, Greece, email: sgiannissi@ipta.demokritos.gr,venets@ipta.demokritos.gr 2National Technical University of Athens, School of Chemical Engineering, Department of Process Analysis and Plant Design, Heroon Polytechniou 9, 15780 Zografou, Greece, email: n.markatos.@ntua.gr 3Department of Energy and Resources Management Engineering, University of West Macedonia, Kozani, Greece, email: bartzis@uowm.gr 4Health and Safety Laboratory, Buxton, Derbyshire, SK17 9JN, United Kingdom, email: Deborah.Willoughby@hsl.gov.uk, Mark.Royle@hsl.gov.uk

2. OUTLINE • Objectives • HSL (Health and Safety Laboratory) Experiments • Test1 (test chosen for simulation) • Test1-Humidity Effect • Modeling Strategy • Physics • Numerics • Results • Conclusions

3. OBJECTIVES • Validation of the CFD code, ADREA-HF, for its performance in simulation of cryogenic releases. Test1 of the HSL experiments (LH2 release experiments) is chosen for simulation. • Examination of the humidity effect on the hydrogen vapor dispersion. Water vapor liquefaction and solidification due to the cold, hydrogen cloud (20K) Heat liberation (latent heat of liquefaction and solidification) H2 vapor cloud more buoyant

4. HSL (HEALTH AND SAFETY LABORATORY) EXPERIMENTS1 • 4 LH2 release tests with spill rate 60lt/min Photograph taken from HSL 1Willoughby, D.B., Royle, M., Experimental Releases of Liquid Hydrogen, 4th International Conference on Hydrogen Safety, San Francisco, California-USA, ICHS , Paper 1A3, 2011

5. TEST1 • Release and weather conditions Photographs taken from HSL

6. TEST1 • Release and weather conditions Site layout (not drawn to scale)

7. MODELING STRATEGY Physics (1/3) • Multi-phase multi component RANS CFD calculation using ADREA-HF CFD code. • 3-D transient, fully compressible conservation equations for mixture mass, mixture momentum, mixture enthalpy, hydrogen mass fraction and water mass fraction (when ambient humidity was taken into account). • Phase distribution: Non vapor phase (liquid+solid) of component-I appears when the mixture temperature falls below the mixture dew temperature, which is calculated using the Raoult’s law for ideal gases. The solid phase of component-I appears when the mixture temperature drops below the freezing point. • Standard k-ε with buoyancy effect term. • One dimensional, transient energy (temperature) equation inside the ground. The ground has the concrete’s properties.

8. MODELING STRATEGY Physics (2/3) • In presence of solid H2O (ice), mixture dynamic viscosity is calculated using 2 different approaches: • Ice viscosity function of temperature • The liquid H2O viscosity correlation used below the FP • Constant ice viscosity • Equal to the water viscosity at freezing point

9. MODELING STRATEGY Physics (3/3) Initial conditions: • To obtain the initial conditions of wind speed, ambient temperature and turbulence the procedure that followed consists of two steps: • One dimensional (in the z-direction) problem was solved to obtain the wind profile according to the experimental data. Neutral atmospheric conditions were assumed. • Three dimensional, steady problem was solved with initial conditions the ones calculated by the previous step (the wind direction was in line with the release). • The transient problem with hydrogen release was solved using as initial conditions the ones derived by the second step. In the case with humidity, additional initial condition for the water vapor mass fraction (5.34∙10-3) was used in the whole domain, calculated by the experiment’s relative humidity. Boundary conditions: • Inlet: The values of all variables were the same as the initial conditions. • Source: The source was modeled as two phase jet. The void fraction of the vapor phase is calculated by assuming isenthalpic expansion from 2 bars (inside the tanker) to 1.2 bars (after the valve is open) and is equal to 71.34%. Temperature, pressure and horizontal velocity were set equal to 21K, 1.2 bars and 6.02 m/s respectively.

10. MODELING STRATEGY Numerics • First order fully implicit scheme for time integration. • First order upwind scheme for discretization of the convective terms • ILU(0) preconditioned BiCGStab solver for the algebraic systems (parallel) • Initial time step 10-4 • Courant number restriction (CFL<2) Figure from Edes (GUI of ADREA-Hf code)

11. RESULTS (1/6) Hydrogen concentration history at locations downwind the release point

12. RESULTS (2/6) Hydrogen concentration history at different heights

13. RESULTS (3/6) Duration 12 sec no humidity humidity

14. RESULTS (4/6) t = 20 sec no humidity humidity

15. RESULTS (5/6) H2vapor volume fraction contours H2O non vapor mass fraction contours t = 20 sec

16. RESULTS (6/6) Temperature contours H2O non vapor mass fraction contours t = 20 sec

17. CONCLUSIONS (1/2) • Multi-phase, multi component CFD calculations have been performed with ADREA-HF code to simulate HSL test-1 LH2 release. The working fluid was assumed to be composed of dry air (gas), water (vapor/liquid/solid) and h2 (vapor/liquid) • Predicted concentration histories with humidity are in better agreement with the experiment compared to the case without humidity. • It has been verified that the H2-humid air cloud becomes more buoyant than when neglecting the humidity, due to the heat liberation by the water vapor condensation/solidification. • Predictions with humidity were found sensitive to the way mixture molecular viscosity is modeled in case of presence of solids (ice). The assumption that ice viscosity follows the liquid viscosity formula below the freezing point gave good results.

18. CONCLUSIONS (2/2) • Predictions show that including humidity reduces horizontal distance to LFL cloud by 40% (almost 10m) and increase the height to LFL cloud (almost 1m) in the present case. • Further work on the humidity effects is necessary to support present findings

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