In the present study, a systematic experimental investigation on the effect of a circular disk obstacle placed axi-symmetrically in the line of a vertical helium jet is presented. The obstacle is placed within the 2 m3 enclosure of AIHMS facility. The location of the obstacle and volume Richardson number have been varied parametrically and the results are compared with those of the free jet with obstacle. The experimental data shows that the obstacle enhances mixing near the obstacle, decreases transport of helium to upper regions of the enclosure and increases transport to lower regions of the enclosure. This effect decreases with increase in the distance between the obstacle and the jet exit. The effect is more pronounced at higher jet velocities i.e. at lower values of volume Richardson number. The experimental database presented can be used for validation of CFD models, grid independence studies, and gaining user experiences before complex problems on helium/hydrogen distribution in confined spaces are taken up. © 2018 Elsevier Ltd

Vasudevan Raghavan

Department of Mechanical Engineering

Sarit Kumar Das

Aneesh Prabhakar

Nilesh Agrawal

Enclosures

Thermal stratification

AIHMS

BUOYANT JETS

COMPLEX PROBLEMS

Experimental database

Experimental investigations

OBSTACLE

Richardson number

User experience

Helium

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Annals of Nuclear Energy

An experimental facility called the AIHMS facility has been installed and commissioned within the IIT Madras premises, to study the phenomenology of hydrogen distribution in confined spaces and generate experimental data for validation of CFD codes before further studies on hydrogen distribution and mitigation in nuclear reactor systems can be carried out. In the present article, experimental studies have been performed on the evolution of the helium stratified layer due to wall temperature induced natural convection. The base case is an isothermal release of helium within the test chamber. Subsequently, two cases are considered in which the wall temperature is above or below the gas temperature in the enclosure. Experimental data has been obtained for gas concentration at seven locations and temperatures at twenty locations within the enclosure. The results show that recirculation regions are formed near the walls. Cooler walls lead to favourable natural convection currents and promote rapid mixing of the stratified layer with lean gas mixture below. On the other hand, warmer walls lead to unfavourable natural convection currents that initially promote stratification and later on promote mixing at a slower rate. In either situation, the rate of mixing is faster than the isothermal case. Repeatability studies have been performed. © 2017 Elsevier B.V.

Nuclear Engineering and Design

Experimental investigations on the evolution of stratified layer of helium in the unventilated vertical cylindrical enclosure of AIHMS facility under wall temperature induced natural convection

Hydrogen is a highly flammable gas and accidental release in confined space can pose serious combustion hazards. Numerical studies are required to assess the formation of flammable hydrogen cloud within confined spaces. In the present study, numerical investigations on the release of helium and hydrogen gases as high-velocity jets and their subsequent distribution inside an unventilated cylindrical enclosure (AIHMS facility) has been carried out as a first step towards numerical studies on hydrogen distribution in confined spaces for safety assessments. Experimental data for jet release of helium at volume Richardson number 0.1 and subsequent distribution has been used as benchmark data. Sensitivity studies on the influence of grid sizes, time-steps and turbulence models are performed. The performance of the validated numerical model is evaluated using statistical performance parameters. Similarity relations are used to determine input parameters for hydrogen jet for corresponding experimental data with helium jets. Finally, the mixing and flammability aspects of hydrogen distribution inside the enclosure are studied using four numerical indices that quantify mixing and deflagration potential of a distribution. It is concluded that the helium experiments can be used for validation of numerical models for hydrogen safety studies and any one of the similarity relationships, viz., equal buoyancy, equal volumetric flow, or equal concentration can be used for assessing the behaviour of hydrogen release and distribution within confined spaces. © 2017 Hydrogen Energy Publications LLC

International Journal of Hydrogen Energy

Numerical modelling of isothermal release and distribution of helium and hydrogen gases inside the AIHMS cylindrical enclosure

Hydrogen leakages into enclosed spaces may occur in hydrogen storage and usage facilities and in nuclear power plants (NPP) following a severe accident. In the absence of either mitigation or combustion processes, hydrogen leaked into the enclosed space may accumulate and form large cloud of explosive mixture with air. This, when gets ignited, can lead to a strong deflagration or even detonation and cause huge threat to both life and property. In NPP, such events can cause over-pressurization of the containment, causing problems in the structural integrity of the containment and consequently result in the leakage of radioactivity into the environment. The present study reports the experimental investigation of the phenomenology of hydrogen distribution inside a cylindrical test enclosure (AIHMS). Different hydrogen leak scenarios are experimentally simulated using helium gas, which is its inert surrogate. The effect of helium release velocities on mixing and distribution of helium within the enclosure, for different quantities of helium released has been experimentally investigated. The experimental studies are conducted in a test enclosure having a volume of around 2 cubic-meters, specifically designed for the purpose and the results have been presented systematically. © 2016 Hydrogen Energy Publications LLC

Experimental investigation on helium distribution and stratification in unventilated vertical cylindrical enclosure – Effect of jet release rates and total release volume

Hydrogen generation during the progression of an accident in a nuclear reactor and its release into the containment comprise an important safety concern in the management of severe accidents in nuclear power plants. The distribution of hydrogen within the containment has important bearing on possibility, mode, and consequence of combustion in the containment. Hence, several small-and large-scale facilities have been built to study the distribution of released hydrogen. Further, several numerical studies and intercomparison exercises on hydrogen distribution have been carried out. The present review summarizes the experimental and numerical studies on hydrogen distribution and suggests opportunities for further studies. © 2015 Taylor and Francis Group, LLC.

Heat Transfer Engineering

Hydrogen distribution in nuclear reactor containment during accidents and associated heat and mass transfer issues-A review

Development of a model evaluation protocol for CFD analysis of hydrogen safety issues the SUSANA project

An experimental study on the effect of coaxial circular disk obstacle on helium jet distribution inside the unventilated enclosure of AIHMS facility

Journal	Data powered by TypesetAnnals of Nuclear Energy
Publisher	Data powered by TypesetElsevier Ltd
ISSN	03064549
Open Access	No