This paper presents a series of experiments on the effectiveness of existing mechanical ventilation systems during accidental hydrogen releases in confined spaces, such as underground garages. The purpose was to find the mass flow rate limit, hence the TPRD diameter limit, that will not require a change in the ventilation system. The experiments were performed in a 40 ft ISO container in Norway, and hydrogen gas was used in all experiments. The forced ventilation system was installed with a standard 315 mm diameter outlet. The ventilation parameters during the investigation were British Standard with 10 ACH and British Standard with 6 ACH. The hydrogen releases were obtained through 0.5 mm and 1 mm nozzles from different hydrogen reservoir pressures. Both types of mass flow, constant and blowdown, were included in the experimental matrix. The analysis of the hydrogen concentration of the created hydrogen cloud in the container shows the influence of the forced ventilation on hydrogen releases, together with TPRD diameter and reservoir pressure. The generated experimental data will be used to validate a CFD model in the next step.

This work focuses on the experimental and numerical investigation of maximum overpressure and pressure dynamics during ignited hydrogen releases in a storage enclosure, e.g., in marine vessel or rail carriage, with limited vent size area, i.e., the pressure peaking phenomenon (PPP) revealed theoretically at Ulster University in 2010. The CFD model previously validated against small scale experiments in a 1 m³ enclosure is employed here to simulate real-scale tests performed by the University of South-Eastern Norway (USN) in a chamber with a volume of 15 m³. The numerical study compares two approaches on how to model the ignited hydrogen release conditions for under-expanded jets: (1) notional nozzle concept model with inflow boundary condition, and (2) volumetric source model in the governing conservation equations. For the test with storage pressure of 11.78 MPa, both approaches reproduce the experimental pressure dynamics and the pressure peak with a maximum 3% deviation. However, the volumetric source approach reduces significantly the computational time by approximately 3 times (CFL = 0.75). The sensitivity analysis is performed to study the effect of CFL number, the size of the volumetric source and number of iterations per time step. An approach based on the use of a larger size volumetric source and uniform coarser grid with a mesh size of a vent of square size is demonstrated to reduce the duration of simulations by a factor of 7.5 compared to the approach with inflow boundary at the notional nozzle exit. The volumetric source model demonstrates good engineering accuracy in predicting experimental pressure peaks with deviation from −14% to +11% for various release and ventilation scenarios as well as different volumetric source sizes. After validation against experiments, the CFD model is employed to investigate the effect of cryogenic temperature in the storage on the overpressure dynamics in the enclosure. For a storage pressure equal to 11.78 MPa, it is found that a decrease of storage temperature from 277 K to 100 K causes a twice larger pressure peak in the enclosure due to the pressure peaking phenomenon.

This paper presents experimental results of the rapid phase transition of liquid CO₂released from the bottom of a small rectangular duct (BR). The aim is to consider the factors influencing the phase transitions and the release rate if the rupture area is below the liquid level. The tests are initiated by rupturing the diaphragm separating the test section from an atmospheric chamber. Pressure and temperature measurements are used to analyze the phase transition. Also, a high-speed shadowgraph technique is used to visualize the waves. The results are compared with previous top-release tests (TR), where the rupture area is sited above the liquid level. Test results show that the duct’s outlet flow behavior for the BR differs from the TR tests, wherein the gas/two-phase flow is choking. In the BR tests, the shadowgraph images demonstrate that when the liquid/two-phase flows out, the liquid/vapor interface remains nearly fixed until it breaks up. This behavior indicates that the headspace vapor has little influence on the initial evaporation in the BR tests. The results from the current BR tests indicate a lower degree of superheating than in the TR tests (it decreases by 34% for LVF = 66.0%), and the evaporation rate is 1.2–1.8 times faster.Graphical abstract

This article investigates doctorateness in Norway by evaluating the juridical regulations for doctoral studies at all PhD-awarding universities and university colleges according to the following categories: admission, compulsory training, the PhD dissertation, supervision and evaluation, and completion. Descriptive qualitative document analyses were applied. As such, the article contributes to the growing field of knowledge on the assessment of PhD education. The findings indicate that the majority of the PhD regulations align on several descriptors of doctorateness. However, the article suggests improving the reliability of doctorateness by standardizing and unifying some areas in the regulations.