The study of compressed hydrogen release from high-pressure storage systems has practical application for hydrogen and fuel cell technologies. Such releases may occur either due to accidental damage to a storage tank or connecting piping, or due to failure of a pressure release device (PRD). Understanding hydrogen behavior during and after the unintended release from a high pressure storage device is important for development of appropriate hydrogen safety codes and standards and for the evaluation of risk mitigation requirements and technologies. In this paper, the natural and forced mixing and dispersion of hydrogen released from a high pressure tank in a partially enclosed compartment is investigated using analytical models. Simple models are developed to estimate the volumetric flow rate through a choked nozzle of a high pressure tank. The hydrogen released in the compartment is vented through buoyancy induced flow, or through forced ventilation. The model is useful in understanding the important physical processes involved during the release and dispersion of hydrogen from a high pressure tank, into a compartment with vents at multiple levels. Parametric studies are presented to identify the relative importance of various parameters such as diameter of the release port and air changes per hour (ACH) characteristic of the enclosure. The model is used to predict the compartment over-pressure as a function of the size of the release port. Conditions that can lead to major damage of the compartment due to over-pressure are identified. Results of the analytical model indicate that the fastest way to reduce flammable levels of hydrogen concentration in a compartment is accomplished by blowing through the vents. Model predictions for forced ventilation are presented to effectively and rapidly reduce the flammable concentration of hydrogen in the compartment following the release of hydrogen from a high pressure tank.
Citation: Technical Note (NIST TN) -
NIST Pub Series: Technical Note (NIST TN)
Pub Type: NIST Pubs
Hydrogen, High Pressure Release, Dispersion