1. CFD computations of liquid hydrogen releases
JIP Meeting, May 2011, Bergen, Norway
CFD computations of liquid hydrogen releases
Ichard M.1, Hansen O.R.1, Middha P.1 and Willoughby D.2 1GexCon AS 2HSL th International Conference on Hydrogen Safety, San Francisco, USA September 12-14, 2011

2. Outline Introduction Previous work with FLACS
4th ICHS, Sep 12-14, 2011
Outline
Introduction
Previous work with FLACS
Multiphase flow modeling in FLACS
Simulations of HSL experiments
Conclusions

3. Liquid hydrogen releases
4th ICHS, Sep 12-14, 2011
Liquid hydrogen releases
Spills of liquid hydrogen are a hazardous scenario in a variety of settings (industrial, transport, etc.)
There are still several uncertainties in modelling LH2 spills
Current work uses recent HSL experiments as a basis for evaluating new spill models in FLACS

4. 4th ICHS, Sep 12-14, 2011
FLACS CFD code
Specifically developed for process safety applications (explosion & dispersion)
Shallow water equations solved for liquid spill modelling
Obstacles can affect the liquid motion
ABL modelled by imposing velocity, temperature & turbulence profiles at inlet boundaries
Pasquill-Gifford stability classes used to represent atmospheric stability

5. Previous work with FLACS
4th ICHS, Sep 12-14, 2011
Previous work with FLACS
The BAM experiments
LH2 releases between buildings (0.37 kg/s; duration 125 s)
The NASA experiments
LH2 releases on flat terrain (11.5 kg/s; duration 35 s)
Significant efforts in LNG related work
Burro, Coyote, Maplin Sands and Wind tunnel experiments simulated (MEP – Hansen et al., 2010)

6. Multiphase flow modelling in FLACS
4th ICHS, Sep 12-14, 2011
Multiphase flow modelling in FLACS
The Homogeneous Equilibrium Model (HEM) used for modeling two-phase flows
Both phases assumed to be in local thermal and kinematic equilibrium
Two main advantages:
Limited information about the source is needed
Conservation equations are similar to single phase flow equations
One main disadvantage:
The assumption of equilibrium (fails for large particles)

7. Multiphase flow modelling in FLACS (2)
4th ICHS, Sep 12-14, 2011
Multiphase flow modelling in FLACS (2)
Model for liquid deposition on obstacles
Rain-out is due to jet impingement on obstacles: rain-out is controlled by the momentum of the jet
The mass of liquid that rains out is directly transferred to the pool model

8. Experimental Description
4th ICHS, Sep 12-14, 2011
Experimental Description
The HSL experiments (4 tests in total):
2 vertically downward releases 100 mm above ground (Tests 6 and 10)
1 horizontal release 860 mm above ground (Test 7)
1 horizontal release on the ground (Test 5)
Release rate: 60 l/min

9. Simulations of HSL experiments
4th ICHS, Sep 12-14, 2011
Simulations of HSL experiments
Estimation of the source term (ST):
Reservoir: P0=2 bar T0=Tsat(P0)
Volumetric flow rate known: 60 l/min
Need to obtain the volume fraction of gas at the exit orifice
Sensitivity study - different gas volume fraction assumed at the exit orifice:

10. Simulations of HSL experiments (2)
4th ICHS, Sep 12-14, 2011
Simulations of HSL experiments (2)
Approach: Simulate Test 7 and find the most appropriate ST:
ST3 or ST4 compare well.
ST1
ST2
ST3
2D cut planes of temperature
ST4
Photograph of Test 7
ST5

11. Simulations of HSL experiments (3)
4th ICHS, Sep 12-14, 2011
Simulations of HSL experiments (3)
Approach: Simulate Test 7 and find the most appropriate ST:
ST4 gives the best predictions overall.
Profile of minimum temperature along the jet axis, 0.75m above the ground

12. Simulations of HSL experiments (4)
4th ICHS, Sep 12-14, 2011
Simulations of HSL experiments (4)
Simulation of Test 6 with ST4:
Downward release 100 mm above the ground
Investigate the effect of air condensation.
Boiling point of O2 is 90K and N2 is 77 K
Volume contour plot of temperature at T=77 K: condensing/freezing zone of N2 and O2

13. Simulations of HSL experiments (5)
4th ICHS, Sep 12-14, 2011
Simulations of HSL experiments (5)
Effect of air condensation (Test 6)
Condensation of O2 and N2 releases energy close to the ground and generates an upward velocity that brings cold hydrogen gas to higher altitudes
Temperature
Velocity
Vertical profiles 1.5 m downstream of exit orifice

14. Simulations of HSL experiments (6)
4th ICHS, Sep 12-14, 2011
Simulations of HSL experiments (6)
Comparison of temperature time series:
0.25m above ground
0.75m above ground
Profiles 1.5m downstream of exit orifice

15. 4th ICHS, Sep 12-14, 2011
Conclusion
An approach to simulate two-phase flows and releases of liquid hydrogen has been presented
A sensitivity study on the source term has shown the importance of having a proper ST model
The condensation of O2 and N2 can have non- negligible effects on the flow field
Condensation of water vapor may also have non- negligible effects
Will be a part of future investigations

16. JIP Meeting, 12-13 May 2011, Bergen, Norway