1. A Numerical / Analytical Model of Hydrogen Release and Mixing in Partially Confined Spaces Kuldeep Prasad, William Pitts and Jiann Yang Fire Research Division National Institute of Standards and Technology Gaithersburg, MD 20899. NHA 2010 Annual Conference e-mail : kprasad@nist.gov

2. Fire safety in confined spaces Hydrogen powered systems –Rising energy demands –Environmental degradation problem Transition to a hydrogen economy poses new safety challenges – Unique fire hazard - Hydrogen behaves differently than conventional fuels – Lack technical data to support standard and code development – partially enclosed compartments. What is the problem?

3. H 2 Flammability, Detection, & Fire Safety To study fire hazards associated with accidental release of hydrogen in residential and commercial settings and to provide sound technical data to support hydrogen fire safety code and standard development. ●Hydrogen fire safety in partially confined spaces ● Release and mixing of hydrogen in confined space. ● Short and long term mixing and dissipatioin. ● Simple theoretical tools, CFD simulations, Experiment ●Hydrogen flammability. ●Standardization of test protocols for hydrogen detection. ●Code and standard activities (NFPA-2)

4. Hydrogen Release as a Point Source Release of hydrogen as a point source. Un-cluttered environment Turbulent hydrogen plume entrains air. Plume reaches ceiling and spreads radially. Buoyant layer separated from ambient air by a density interface.

5. Problem Formulation

6. Conservation Equations Conservation of Hydrogen in upper layer Conservation of total mass in upper layer Constraint Equation Plume Modeling Classical Plume Mixing Model – self similar plume solution Buoyancy Flux Effective origin

7. Hole Burner 1.5 m 0.75 m 1.5 m Sensor 7 (0.65 m) Sensor 6 (0.56 m) Sensor 5 (0.45 m) Sensor 4 (0.37 m) Sensor 3 (0.28 m) Sensor 2 (0.19 m) Sensor 1 (0.09 m) Reduced scale experiments Comparison with Analytical Model

8. Full Scale CFD simulations Comparison with Analytical model Hole Burner

9. Effect of Hydrogen Release Rate Hydrogen Volume FractionHeight of the Interface Compartment Overpressure Volumetric Flow Rates

10. Wind Driven Ventilation of Compartment Assisting Wind Flow Wind assists buoyancy driven flow Opposing Wind Flow Weak wind opposes buoyancy driven flow Opposing Wind Flow Strong wind opposes buoyancy driven flow

11. Wind Driven Ventilation-Steady State Results

12. Forced Venting of Hydrogen: Formulation

13. Forced Venting of Hydrogen : Results

14. Release as a Distributed Source Release of hydrogen under an obstruction. Cluttered environment, Multiple plumes. Buoyant gas mixes rapidly with surrounding air. Well mixed hydrogen air mixture in compartment.

15. Problem Formulation Conservation of hydrogen in compartment Constraint Equation

16. Effect of Vent Area, Location Multiple Vents

17. Conclusions and Future Work Natural and wind driven ventilation of hydrogen released in an accidental manner in a partially enclosed compartment. Development of simple analytical models –Validated with reduced scale experiments. –Validated with full scale detailed CFD simulations. Effect of Hydrogen Release Rate Effect of vent cross-sectional area, distance between vents, multiple vents, location of vents. Role of assisting and opposing wind flows Forced ventilation, thermal effects, Effect of surrogate gases (helium). Time to empty a compartment filled with hydrogen gas.