Experimental investigation on helium distribution and stratification in unventilated vertical cylindrical enclosure e Effect of jet release rates and total release volume Aneesh Prabhakar a , Nilesh Agrawal b , Vasudevan Raghavan a , Sarit K. Das a,* a Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, 600036, Tamil Nadu, India b Safety Research Institute, Atomic Energy Regulatory Board, Government of India, Kalpakkam, 603102, Tamil Nadu, India article info Article history: Received 21 April 2016 Received in revised form 15 October 2016 Accepted 18 October 2016 Available online xxx Keywords: AIHMS Transient helium injection Hydrogen leak Diffusion Stratification Buoyant jets abstract 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 accu- mulate 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. Published by Elsevier Ltd. All rights reserved. Introduction Hydrogen is expected to be introduced on a wide scale as a clean energy carrier and as a promising replacement for the traditional carbonized fuels in the drive towards future low carbon society [1e3]. Hydrogen in air has a flammability range between 4 and 75 vol % and detonability range between 18 and 59 vol % and very low ignition energy of 0.02 mJ [4]. As a result, * Corresponding author. E-mail addresses: prabhakaraneesh@gmail.com (A. Prabhakar), nilesh_agrawal@igcar.gov.in (N. Agrawal), raghavan@iitm.ac.in (V. Raghavan), skdas@iitm.ac.in (S.K. Das). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2016) 1 e16 http://dx.doi.org/10.1016/j.ijhydene.2016.10.098 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Prabhakar A, et al., Experimental investigation on helium distribution and stratification in unven- tilated vertical cylindrical enclosure e Effect of jet release rates and total release volume, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.10.098