HYDROGEN SUBSONIC UPWARD RELEASE and DISPERSION EXPERIMENTS in CLOSED CYLINDRICAL VESSEL

1. HYDROGEN SUBSONIC UPWARD RELEASE and DISPERSION EXPERIMENTS in CLOSED CYLINDRICAL VESSEL Denisenko V.P.1, Kirillov I.A.1, Korobtsev S.V.1, Nikolaev I.I.1, Kuznetsov A.V.2, Feldstein V.A.3, Ustinov V.V.3 1 RRC”Kurchatov Institute” Kurchatov Sq., Moscow, 123182, Russia 2 NASTHOL 4, Shenogin str., Moscow, 123007, Russia 3 TsNIIMash 4, Pionerskaya, Korolev, 141070, Russia

2. ABSTRACT Report presents the preliminary experimental results on hydrogen subsonic leakage in a closed vessel under the well-controlled boundary/initial conditions. Formation of hydrogen-air gas mixture cloud was studied for a transient (10 min), upward hydrogen leakage, which was followed by subsequent evolution (15 min) of explosive cloud. Low-intensity (0,46*10-3 m3/sec) hydrogen release was performed via circular (diameter 0.014 m) orifice located in the bottom part of a horizontal cylindrical vessel (about 4 m3). A spatially distributed net of the 24 hydrogen sensors and 24 temperature sensors was used to permanently track the time dependence of the hydrogen concentration and temperature fields in vessel. Analysis of the simultaneous experimental records for the different spatial points permits to delineate the basic flow patterns and stages of hydrogen subsonic release in closed vessel in contrast to hydrogen jet release in open environment. The quantitative data were obtained for the averaged speeds of explosive cloud envelop (50% fraction of the Lower Flammability Limit) propagation in the vertical and horizontal directions. The obtained data will be used as an experimental basis for development of the guidelines for an indoors allocation of the hydrogen sensors. Data can be also used as a new benchmark case for the reactive Computational Fluid Dynamics codes validation.

3. PROJECT GOAL • The general goal of our study is to create an experimental database to be used in ongoing development of the rational (non-empiric) guidelines for a minimal number and spatial allocation of the indoors hydrogen sensors

4. EXPERIMENTAL SYSTEM (VESSEL and SENSORS NET) External (left) and internal (right) views of the experimental chamber

5. LOCATION of the EXPERIMENTAL VESSEL in the PROTECTIVE DOME Schematic draw of protective concrete dome (R = 6 m, h = 6 m, H = 12 m) Air temperature inside the dome 23ºC Relative humidity 64 %

6. SPATIAL ALLOCATION of the GAUGES (HYDROGEN SENSORS + THERMOCOUPLE)in the EXPERIMENTAL VESSEL The adjusting device for gauges allocation (to measure hydrogen concentration and temperature) consists of seven vertical metal rods with 0,006 m diameter, which allows to fix gauge position in rectangular coordinates: Y – along the horizontal chamber axis, X in the meridional cross-section of vessel

7. SENSORS USED in the EXPERIMENTS Thermal Conductivity Gauge TCG-3880 for gas measurement (with open cap) by Xensor Integration (Netherlands) Acoustic sensors with electronic scheme of data process and transmission by RRC ”Kurchatov Institute” The accuracy of absolute concentration measurement is varying from 2 to 5%. The relative measurement accuracy (resolution) of concentration measurements by calibrated sensors at stationary regimes (the absence of convective gas flows) was 0,03% vol.

8. EXPERIMENTAL SYSTEM (GAS CONTROLSYSTEM) The main part of gas mixture conditioning and transport system is the gas mixture preparation device (GMPD), which allows to mix complex gas mixtures (up to 8 components) at the concentration range for every component from 0 to 100% with the step of 1/256 and relative accuracy 0,5%, and to establish and control steady gas flow rate from 5*10-6 to 7*10-4 m3/s (from 20 to 2560 l/h). The gas mixture from the gas mixture preparing device is supplied into experimental chamber through pipe and is released into its internal space trough a letting device. The letting device determines the regime of gas release (diffusion or jet-mixing) and gas velocity at fixed gas flow rate.

9. EXPERIMENTS Formation of hydrogen-air gas mixture cloud was studied for a transient (10 min), upward hydrogen leakage, which was followed by subsequent evolution (15 min) of explosive cloud. Low-intensity ( m3/sec) hydrogen release was performed via circular (diameter 0.014 m) orifice located in the bottom part of a horizontal cylindrical vessel (4 m3).

10. RESULTS of the EXPERIMENTS Time histories for the hydrogen concentrations (% vol.) for the 24 gauges (time duration 0 - 25 min)

11. RESULTS of the EXPERIMENTS HYDROGEN CLOUD EXPANSION and PROPAGATION 10,05 min 1 min 15 min 5 min 25 min 10 min hydrogen concentration in % vol.

12. RESULTS of the EXPERIMENTS The basic flow patterns and stages of hydrogen subsonic release in closed vessel Analysis of the time histories of hydrogen concentration at different spatial points permits to delineate the following basic stages in formation and evolution of hydrogen-air mixture cloud: Step 1 – upward propagation of emerging jet, Step 2 – impinging of jet with ceiling and outward expansion of cloud, Step 3 – downward expansion of cloud from ceiling to floor. The numerical data, received in the current and future test runs, can be used as a basis for empirical correlation, which defines a time dependence of volume of flammable cloud.

13. RESULTS of the EXPERIMENTS Averaged speed of critical concentration (2 % vol.) front propagation For UNVENT 1 run, the numerical values of reactive cloud propagation in upward vertical direction is 0,33 m/sec, in horizontal direction (outward) - 0,055 m/sec. Definition of the averaged speed of critical concentration front movement (between sensor 4 and sensor 21; time duration 0 - 0,5 min)

14. RESULTS of the EXPERIMENTS ( REPRODUCIBILITY ) Reproducibility of the time histories for the three different test runs (sensor 10). For the points, where strong jet-sensors interaction was absent, the experimental data were coincident with the accuracy 0,2 % vol.

15. RESULTS of the EXPERIMENTS Coincident changes of hydrogen concentrations at points of sensors 18 and 24 The proof of symmetrical character of hydrogen flow in the experimental vessel

16. CONCLUSIONS • The experimental set-up for investigating the processes of hydrogen release and mixing at atmospheric pressure in a medium-scale (4 m3), closed horizontal cylindrical vessel was prepared and adjusted. • The first accurate measurements (3 test runs) of the time evolution of explosive hydrogen cloud after hydrogen injection under the well-controlled boundary/initial conditions have been carried out with the help of 24 hydrogen sensors and 24 temperature sensors. • Analysis of the simultaneous experimental records for the different spatial points permits to delineate the basic flow patterns and stages of hydrogen subsonic release in closed vessel in contrast to hydrogen jet release in open environment. The quantitative data were obtained for the averaged speeds of explosive cloud envelop (50% fraction of the Lower Flammability Limit (LFL) – 2 vol.%) propagation in the vertical and horizontal directions. ACKNOWLEDGMENTS This work was supported by the grant (“Codes and Systems for Hydrogen Safety”) from the Russian Ministry of Science and Education and by the EU HYPER project (contract no. 039028).

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