1. SAFETY OF LABORATORIES FOR NEW HYDROGEN TECHNIQUES Heitsch, M., Baraldi, D., Moretto, P., Wilkening, H. Institute for Energy (IE) Petten, The Netherlands ICHS 2007, San Sebastian, Spain

2. Outline • Motivation • Problem Set-up • Geometry • Initial and Boundary Conditions • Selected Results • Conclusions and Continuation of Work ICHS 2007, San Sebastian, Spain

3. Motivation • Assessment of the risk involved in accidental hydrogen releases, • Creation of a decision basis for the placement of hydrogen sensors, • Simulation of hydrogen release in the laboratory: • Assessment of flammability of clouds by size and duration, • Investigation of several hydrogen release scenarios: • Small break low pressure release, • Full cross section release. ICHS 2007, San Sebastian, Spain

4. Problem Set-up: Geometry • Laboratory has dimensions of about 18mx8.5mx3.5m with an approximate volume of 285 m3, • Several test stands to investigate hydrogen sorption in materials, • Lab is ventilated; above each test stand fume hoods are installed, hydrogen sensors underneath all hoods, • Hydrogen system: • 200 bar pressure, total hydrogen mass available is about 1,2 kg, • Pipes and joints distributed at the walls. ICHS 2007, San Sebastian, Spain

5. Problem Set-up: Geometry • Laboratory and CFD model ICHS 2007, San Sebastian, Spain

6. Problem Set-up: Geometry • CFD Model consists of hexahedrals in most locations but also regions of pyramids and tetrahedrals to include hydrogen pipes with 4 mm and 10 mm diameter. • Mesh: about 774250 cells with 518660 hexahedrals. ICHS 2007, San Sebastian, Spain

7. Problem Set-up: Initial and Boundary Cond. • Analysis software used is CFX 10. • Accident happens under normal working conditions in the lab: • Ventilation is working: • Flow speeds at inlets and outlets are used in the code as measured, • A run without hydrogen release to get converged flow conditions as initial guess for the accident, • The total amount of hydrogen available (1,2 kg) is assumed to eject into the lab. The release is idealised; pressure drop in the hydrogen bottle is not considered -> constant flow rate over time. ICHS 2007, San Sebastian, Spain

8. Problem Set-up: Initial and Boundary Cond. • The hydrogen system itself is not modelled, simulation boundaries are located at the open end of the ruptured pipe: • The low pressure scenario assumes a leak at a pipe connector with high pressure loss (sub-critical flow with 100 m/s and 500 m/s), • The high pressure scenario assumes a full cross section break (4 mm diameter) with 50 bar and 100 bar pressure at the pipe outlet. The outlet pressures chosen are based on rough estimates of the internal pressure drop in the hydrogen system at critical outflow conditions (parametric studies). • Heat transfer to walls in modelled. ICHS 2007, San Sebastian, Spain

9. Problem Set-up: Initial and Boundary Cond. • Validation of CFX for relevant phenomena: • Gas mixing in closed space, e.g.: HYJET, ThAI and OECD-SETH tests with helium instead of hydrogen, • Critical outflow: some work by vendor, but needs more data. ICHS 2007, San Sebastian, Spain

10. Problem Set-up: Initial and Boundary Cond. • Leak outflow histories for critical cases (50 and 100 bar): ICHS 2007, San Sebastian, Spain

11. Selected Results: Sub-critical cases • Very low amount of flammable mass: ICHS 2007, San Sebastian, Spain

12. Selected Results: Critical cases • Hydrogen release for the 100 bar case: ICHS 2007, San Sebastian, Spain

13. Selected Results: Critical cases • Flammable mass similar for both pressures: ICHS 2007, San Sebastian, Spain

14. Selected Results: Critical cases • Influence of mesh resolution on flammable mass: ICHS 2007, San Sebastian, Spain

15. Conclusions and Continuation of Work • Simulations of accidental hydrogen release with CFX show that the existing ventilation system in the lab removes almost all hydrogen after about 80 s. Most of the flammable mass is restricted to concentrations below 10%. • CFX proved to be robust enough to include very different length scales (from 4 mm to several metres) in combination with a range of time scales (from milliseconds to minutes) in a single run. ICHS 2007, San Sebastian, Spain

16. Conclusions and Continuation of Work • Continuation of work is focused on: • the inclusion of the hydrogen storage system, • high mesh resolution in the outflow region, • performance of hydrogen deflagration in combination with the acceleration criterion, • more comprehensive application of Best Practice Guidelines. ICHS 2007, San Sebastian, Spain