Pressure peaking phenomenon for indoor hydrogen releases

Abstract

The pressure peaking phenomenon can be observed when hydrogen is released in enclosures with vent(s). The unforeseen physical phenomena of pressure peaking has been described and explained. This phenomenon occurs for hydrogen releases in enclosures where the vent(s), volume, and leak rate are such that there will be no air ingress to the enclosure. Pressure peaking describes the physical phenomenon of a peak in the pressure transient during such a release for some release conditions in a vented enclosure. This phenomenon is pronounced only for gases lighter than air, e.g. hydrogen and helium. For particular release flow rates and vent sizes the peak can be an order of magnitude higher compared to the steady-state overpressure that is reached when the enclosure is fully filled with hydrogen over time. This finding is relevant to all hydrogen applications indoors from a fuel cell in an enclosure or laboratory scale storage up to a forklift in a warehouse. The peak magnitude depends on the release flow rate, hydrogen inventory, enclosure volume and the ventilation area, and potentially can exceed the maximum pressure which the enclosure can withstand. A look up nomogram for applicability of the developed theory that is based on vent area and leak rate has been created for sustained releases. Experimental evidence of the phenomena is described. Reduced analytical equations are presented for the case of a constant flow rate release, and the associated nomogram is presented for use by hydrogen safety engineers and regulators. Highlights  Describes and explains the pressure peaking phenomena for indoor hydrogen releases  Occurs when leak and geometry configuration lead to no air ingress to the enclosure  Nomogram to calculate peak overpressure for constant leak rate in an enclosure  Reduced analytical equations are given  Tools presented for use by hydrogen safety engineers and regulators *Highlights (for review)

Numerical validation of pressure peaking from an ignited hydrogen release in a laboratory-scale enclosure and application to a garage scenario

“…This pressure peaking phenomenon for the unignited release of hydrogen in an enclosure has been well studied analytically [4] and recently validated against experimental data [5]. A detailed explanation of the pressure peaking phenomena for unignited jets, and a simple nomogram can be found in recent work by Brennan et al [36]. The pressure peaking phenomenon for unignited hydrogen releases was validated against experiment results performed by KIT within the HyIndoor project [6].…”

Dispersion of hydrogen release in a naturally ventilated covered car park

“…Previous studies by the authors have focused on unignited [32] and ignited [10] hydrogen release in enclosures where the aim has been to avoid the hazard and associated risk due to the pressure peaking phenomena. Whereas in this work the larger vents mean that overpressure is not the most significant hazard.…”

Effect of Mechanical Ventilation on Accidental Hydrogen Releases—Large-Scale Experiments

“…The release source was located under the car, between the back wheels. TPRDs with diameters larger than 0.5 mm resulted in a flammable cloud, filling the major part of the enclosure in less than 20 s. The author outlined the unacceptable large diameters of TPRD, which lead to high concentrations in a short time, and may result in pressure peaking phenomena described in previous studies, also by authors of this article [18][19][20][21]. Forced ventilation as a mitigation method in the semiclosed space was investigated by Malakhov et al [22].…”