Guidelines and recommendations for indoor use of fuel cells and hydrogen systems

Highlights  Study on pressure peaking for ignited hydrogen releases in enclosures  Description and validation of CFD model for ignited pressure peaking phenomena  Focuses on a small-scale validation case and a real scale residential garage  Heat transfer, vent size and release rate impact on the pressure peak  Pressure peak for ignited release 2 orders of magnitude greater than unignited case *Highlights (for review)

Section: Introductionmentioning

confidence: 99%

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

Hussein

Brennan

Shentsov

et al. 2018

“…We present in here a preliminary comparison of the helium concentration distribution versus the theoretical model of Linden et al [8]. This model is generally used in hydrogen safety precalculations of two vented idealized fuel cell configurations [26], similar to the geometry studied 21 in this paper. In situations where a bi-layer distribution takes place inside the two vented cavity, the model can be correctly served to predict the height of the separating interface, in addition to the homogeneous concentration at the top.…”

Section: Les Predictions Versus Linden's Pre-safety Calculation Modelmentioning

confidence: 98%

Highly resolved large eddy simulations of a binary mixture flow in a cavity with two vents: Influence of the computational domain

Saikali

Bernard-Michel

Sergent

et al. 2019

In this article, numerical results from a highly resolved large eddy simulations (LES) of an airhelium buoyant jet developing in a two vented cavity are presented. The simulated configuration mimics the helium-release experiment carried out at CEA Saclay in the framework of security assessment of indoor used hydrogen-based systems. The height of the enclosure was chosen so that a laminar-turbulent transition occurs approximately at the middle of the upstream direction. An exterior region, of different spatial dimensions, has been modelled in the computational domain in order to move the boundary conditions away from the vent surface and to approach the natural inlet/outlet conditions. A sensitivity analysis regarding the size of the exterior region is presented to define the minimum horizontal extension so that the flow inside the cavity is not furthermore influenced by bigger computational domains. We observe mainly that applying an ambient equilibrium-hydrostatic pressure outlet condition directly on the surface of the vent reduces the volume of the air inflow, and thus predicts larger helium mass inside the cavity, in contrary with the cases where an exterior region is considered. A qualification analysis shows that the sub-grid scale model plays a small role in the calculations and thus implies that the LES predictions approach the direct numerical simulation (DNS) solution. Analysis carried out on the time-averaged helium field depict a stratified regime not situated in the framework of the theoretical model used in safety pre-calculations.

“…As previously mentioned, indoor use of hydrogen and fuel cell systems covers a wide range of potential scenarios; a fuel cell in a 1 m 3 cabinet and a forklift in a 1000 m 3 warehouse are just two of many possible cases. The potential leak rates encountered may range from fractions of a gram per second (g/s) for partial ruptures of low pressure pipes, close to 0.5 kg/s when considering a constant release following full bore rupture of a PRD with a diameter about 5 mm on a 70 MPa storage tank, or indeed larger rates if releases from higher pressures or pipe diameters are taken into account.…”

Section: Problem Descriptionmentioning

confidence: 99%

“…Overpressure versus time for a constant mass flow rate release of 390 g/s into enclosure volumes of 10 m 3, 30 m3 and 100 m 3 with a 20x20 cm vent.…”

mentioning

confidence: 99%

Pressure peaking phenomenon for indoor hydrogen releases

Brennan

Molkov

2018

Self Cite

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)