Boundary layer theory approach to the concentration layer adjacent to the ceiling wall of a hydrogen leakage: Axisymmetric impinging and far regions

As hydrogen leaks into a partially open space with a ceiling wall, a boundary layer of hydrogen can be constructed under that wall due to the impingement on the wall and the buoyancy force. The resulting boundary layer can be divided into two regions, namely the stagnation-point region and the far region. When the geometry of the source of the hydrogen leak is circular, such as a pinhole or an o-ring, the behavior of leakage flow will be axisymmetric due to the resulting radial jet. In contrast, when the geometry of the source of the hydrogen leak is planar, such as a crack, the behavior of leakage flow will be planar due to the resulting planar jet. Previously, we studied the planar case in the context of both the stagnation-point flow region [El-Amin MF, Kanayama H. Boundary layer theory approach to the concentration layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy 2008; 33(21): 6393–00] and the far region [El-Amin MF, Inoue M, Kanayama H. Boundary layer theory approach to the concentration layer adjacent to a ceiling wall of a hydrogen leakage: far region. Int J Hydrogen Energy 2008; 33(24):7642–7]. This paper is concerned with both the stagnation-point flow region and the far region of the axisymmetric concentration boundary layer adjacent to a ceiling wall. Flow in the stagnation-point region is treated as Hiemenz flow, while it is treated as Blasius flow in the far region. The current results are compared with the planar cases [El-Amin MF, Kanayama H. Boundary layer theory approach to the concentration layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy 2008; 33(21): 6393–00; El-Amin MF, Inoue M, Kanayama H. Boundary layer theory approach to the concentration layer adjacent to a ceiling wall of a hydrogen leakage: far region. Int J Hydrogen Energy 2008; 33(24):7642–7] for both stagnation-point flow and far regions. Both momentum and concentration boundary layer thicknesses are estimated, as well as the local friction factor.     

Investigation of concentration measurement for hydrogen leakage with a new calibration visual approach

Hydrogen leakage concentration rapid measurement is the key issue for hydrogen application as hydrogen leakage is easy to cause hydrogen safety issues such as hydrogen explosions. Non-invasive visual measurement method such as the schlieren measurement technique is the prospective solution. However, the specific relationship between the hydrogen leakage concentration and schlieren image gray remains unclear, which leads that the schlieren technique procedure is developed for visualization and acquiring qualitative information only. This paper aims to decouple the hydrogen leakage concentration from the complicated schlieren image information, and find the mapping relationship between the hydrogen leakage concentration and schlieren image gray, hence realizing a quantitative hydrogen leakage concentration analysis. Therefore, a hydrogen leakage visualization experimental bench is established to simulate and measure hydrogen leakage by a series of experiments under different leakage concentrations. The mapping relationship between the hydrogen leakage concentration and schlieren image gray is obtained by the experiments using the schlieren technique. Then, a new calibration schlieren technique with the function of visually measuring hydrogen leakage concentration is developed and verified under 80% hydrogen leakage concentration. Results of the trials demonstrated the ability of the proposed technique successfully measure concentration distributions with satisfactory accuracy.     

Analytical and numerical predictions of hydrogen gas flow induced by wall and corner leakages in confined space

This contribution addresses a newly developed semi-analytical model coupling the zone model, virtual point source buoyancy plume theory and mirror theory to predict the gas flow behaviors of leaked hydrogen restricted by a wall or a corner in confined space with an opening. The effects of leaked hydrogen mass flux, opening geometry and the leakage location on interface height, outflow velocity and hydrogen molar fraction in upper layer, were thoroughly investigated at steady stage. A computational fluid dynamics tool, FLACS, was employed to simulate the dispersion process in different leakage scenarios and validate the capability of the derived analytical model. The results show that in all center, wall and corner leakage circumstances, the interface height declines with larger leakage mass flux, whereas the outflow velocity and hydrogen molar fraction change inversely. The interface height, outflow velocity and hydrogen molar fraction are positively, negatively and negatively correlated with the opening dimension, respectively. The opening height plays a more important role in determining the interface height and hydrogen molar fraction but hardly affects the outflow velocity. The interface height keeps unchanged with varying leakage locations when other parameters remain constants. However, according to the mirror theory the outflow velocities in corner and wall leakage conditions are 0.63 and 0.4 times of those in center leakage case. Meanwhile, the hydrogen molar fractions of corner and wall leakages are 1.59 and 2.52 times of the ones in center leakage. All these ratios are validated by the corresponding analytical and numerical predictions. The credibility of the analytical model is verified by the good agreement with the numerical estimations.     

A CFD simulation of hydrogen dispersion for the hydrogen leakage from a fuel cell vehicle in an underground parking garage

In the present study, the dispersion process of hydrogen leaking from an FCV (Fuel Cell Vehicle) in an underground parking garage is analyzed with numerical simulations in order to assess hazards and associated risks of a leakage accident. The temporal and spatial evolution of the hydrogen concentration as well as the flammable region in the parking garage was predicted numerically. The volume of the flammable region shows a non-linear growth in time with a latency period. The effects of the leakage flow rate and an additional ventilation fan were investigated to evaluate the ventilation performance to relieve accumulation of the hydrogen gas. It is found that expansion of the flammable region is delayed by the fan via enhanced mixing near the boundary of the flammable region. The present numerical results can be useful to analyze safety issues in automotive applications of hydrogen.     

A new approach to optimize the performance of a hydrogen reservoir using activated carbon as the storing material

We have developed a new approach in order to compute the optimal way of filling as efficiently as possible an hydrogen reservoir using activated carbon as the storing material. Our approach combines finite element computation with multi objective optimization techniques based on the Fast Pareto Genetic Algorithm (FPGA) to find an ensemble of optimal solutions known as the Pareto front. We have illustrated our method by studying a small cylindrical reservoir. We were able to find a 7-point filling function (i.e. the input flow as a function of time) giving the shortest filling time to reach a stored hydrogen mass for a given heat transfer coefficient while keeping the reservoir internal temperature and pressure under their maximal safe values.     

Research on the hydrogen injection strategy of a direct injection natural gas/hydrogen rotary engine considering apex seal leakage

The purpose of the present paper is to investigate the hydrogen injection strategy on the combustion performance of a natural gas/hydrogen rotary engine. Considering that apex seal leakage (ASL) is an inevitable problem in the actual working process of a rotary engine, the action of ASL cannot be ignored for an in-depth study of its combustion performance. Therefore, in this paper, a 3D dynamic simulation model that put the effect of ASL into consideration was established. Furthermore, based on the established 3D model, the combustion process of a natural gas/hydrogen rotary engine under various hydrogen injection angle (HIA) and hydrogen injection timing (HIT) was investigated. The results indicated that the hydrogen jet flow first impacted on the rotor wall after entering the cylinder, and then diffused under the action of the vortexes in the cylinder. Therefore, the HIA and HIT could change the hydrogen distribution by changing the hydrogen impact location and the intensities of the vortexes in the cylinder. In addition, the ideal hydrogen distribution at the ignition timing which could improve the combustion efficiency was given. That is, under the premise of ensuring minimized hydrogen leakage, the hydrogen should mainly distribute in the middle and the front of the cylinder, and a high hydrogen concentration is maintained near the spark plug.     

An experimental investigation of the dissipation mechanisms in the suction side boundary layer of a turbine blade

The present work is part of an extensive experimental activity carried out by the authors in recent years aimed at investigating the boundary layer transition phenomenon in turbine blades. The large scale of the cascade and the use of advanced LDV instrumentation and precision probe traversing mechanism resulted in high degree of spatial resolution and high accuracy of measurements. The main dissipation mechanism determining the profile losses in turbomachinery blades is the work of deformation of the mean motion within the boundary layer operated by both viscous and turbulent shear stresses. In the present paper, the local viscous and turbulent deformation works have been directly evaluated from the detailed measurements of boundary layer mean velocity and Reynolds shear stress. The results show the distributions and the relative importance of the viscous and turbulent contributions to the loss production, in relation with the boundary layer states occurring along the turbine profile.     

Analysis of convective momentum and wall heat transfer: application to vortex boundary layer interaction

The main topic of this paper is the analysis of momentum and heat transfer mechanisms occurring inside a disturbed boundary layer. This analysis is carried out based on a phenomenological decomposition using von Karman’s integral equations, in which appear terms that account for several contributions: the flat plate term, and the unsteady and external gradient terms.This method is applied to the interaction between a single transverse vortex and a boundary layer developing on a flat plate. Based on numerical simulations, we present a qualitative and quantitative study of the behavior of momentum and heat wall transfer described by the terms resulting from the phenomenological decomposition. Finally, the time-dependent behavior of the analogy factor is investigated.     

Effect of the position and the area of the vent on the hydrogen dispersion in a naturally ventilated cubiod space with one vent on the side wall

The design of ventilation system has implications for the safety of life and property, and the development of regulations and standards in the space with the hydrogen storage equipment. The impact of both the position and the area of a single vent on the dispersion of hydrogen in a cuboid space (with dimensions L x W x H = 2.90 × 0.74 × 1.22 m) is investigated with Computational Fluid Dynamics (CFD) in this study. Nine positions of the vent were compared for the leakage taking place at the floor to understand the gas dispersion. It was shown a cloud of 1% mole fraction has been formed near the ceiling of the space in less than 40 s for different positions of the vent, which can activate hydrogen sensors. The models show that the hydrogen is removed more effectively when the vent is closer to the leakage position in the horizontal direction. The study demonstrates that the vent height of 1.00 m is safer for the particular scenario considered. The area of the vent has little effect on the hydrogen concentration for all vent positions when the area of the vent is less than 0.045 m² and the height of the vent is less than 0.61 m.     

Effects of Fe0 and Ni0 nanoparticles on hydrogen production from cotton stalk hydrolysate using Klebsiella sp. WL1316: Evaluation of size and concentration of the nanoparticles

Fe⁰ and Ni⁰ nanoparticles (NPs) of certain size were synthesized and added to the hydrogen production system from cotton stalk hydrolysate using Klebsiella sp. WL1316. Fe⁰ and Ni⁰ NPs with a size of 50 nm at all concentrations effectively improve hydrogen production during mid to late fermentation stages; particularly, the highest daily hydrogen production obtained following treatment with 50 nm Fe⁰ NPs at 30 mg/L fermented for 96 h significantly increased by 61% comparing to the control treatment. The reducing sugar consumption in cotton stalk hydrolysate and ΔOD₆₀₀ could be improved to some extent by Fe⁰ and Ni⁰ NPs supplementation. Addition of Fe⁰ or Ni⁰ NPs of 50 nm at a concentration of 30 mg/L resulted in enhanced cumulative hydrogen production with improvement of hydrogen yield reached higher than 20%, and the values of Y(H₂/S) were all higher than 90 mL/g _substrate, reflecting good hydrogen production and substrate consumption. The analysis of the main soluble metabolites profile revealed that supplementation with Fe⁰ and Ni⁰ NPs of suitable size and concentration may decrease the metabolic flux in the competitive branch of hydrogen production and increase the metabolic flux of the key node that leads to hydrogen generation, thus promoting biohydrogen synthesis.     

Sustainability of hydrogen supply chain. Part II: Prioritizing and classifying the sustainability of hydrogen supply chains based on the combination of extension theory and AHP

The purpose of this study is to develop a method for prioritizing and classifying the sustainability of hydrogen supply chains and assist decision-making for the stakeholders/decision-makers. Multiple criteria for sustainability assessment of hydrogen supply chains are considered and multiple decision-makers are allowed to participate in the decision-making using linguistic terms. In this study, extension theory and analytic hierarchy process are combined to rate the sustainability of hydrogen supply chains. The sustainability of hydrogen supply chains could be identified according to the synthesis correlation degrees to each classical domain. Finally, an illustrative case is studied by the proposed method, and the results show that the proposed method is feasible for prioritizing and classifying the sustainability of hydrogen supply chains.     

Investigation on the decarbonization of shipping: An approach to hydrogen and ammonia

Global warming and greenhouse gas emissions are today's major challenges for sustainable industrial developments, and shipping is an important key element of the industrial chain. However, maritime transportation is responsible for 3.1% of total CO₂ emissions worldwide, and International Maritime Organization estimates that it will continue to increase if no measure is taken. In this perspective, alternative fuels are promising solutions to reach the zero-carbon shipping aim. This paper investigates zero-carbon fuels and their power generation solutions to eliminate ship-sourced CO₂ emissions. Hydrogen and ammonia are analyzed to use in a fuel cell according to five different criteria: safety, cost, storage, sustainability, and environmental impact. Criteria weightings are found according to expert points by using the analytic hierarchy process. While the safety and environmental impacts have a major effect on the results, sustainability, storage, and cost are lined up, respectively. A final comparison table is formed by changing weightings for each criterion regarding maritime industry conditions. Sensitivity analysis of the results is carried out with different scenarios to show the reliability of the handled analysis. As a result, ammonia is marginally showed better performance against hydrogen for shipping with applied criteria in this work. This study highlights that shipping has strong options such as ammonia and hydrogen on the road of decarbonization and ammonia can play an important role in the transition to zero-carbon shipping.     

Dehydrogenation of a liquid organic hydrogen carrier compound 1-(3-cyclohexylpropyl)-3-ethylcyclohexane: A density functional theory study

As a compound for liquid organic hydrogen carrier (LOHC) applications, 1-(3-cyclohexylpropyl)-3-ethylcyclohexane was designed and its dehydrogenation reaction was investigated using density functional theory calculations. To check how this compound could be stable, vibrational frequency analysis and formation energy calculations were conducted. Our findings revealed that this LOHC compound was dynamically and chemically stable. Using Mulliken population analysis, the dehydrogenation process was clearly explained. To reduce the dehydrogenation energy, different substituents, such as N, Cl, and Br were used. Our results suggested that N-substitution could be potentially suitable to lower the dehydrogenation energy. Reaction barriers of pristine and N-substituted systems for dehydrogenation reactions were investigated through nudged elastic band methods. In addition, the gap between HOMO and LUMO was calculated to check chemical reactivity.     

Influence of the type of siliceous material used as intermediate layer in the preparation of hydrogen selective palladium composite membranes over a porous stainless steel support

In this work, several composite membranes were prepared by Pd electroless plating over modified porous stainless steel tubes (PSS). The influence of different siliceous materials used as intermediate layers was analyzed in their hydrogen permeation properties. The addition of three intermediate siliceous layers over the external surface of PSS (amorphous silica, silicalite-1 and HMS) was employed to reduce both roughness and pore size of the commercial PSS supports. These modifications allow the deposition of a thinner and continuous layer of palladium by electroless plating deposition. The technique used to prepare these silica layers on the porous stainless steel tubes is based on a controlled dip-coating process starting from the precursor gel of each silica material. The composite membranes were characterized by SEM, AFM, XRD and FT-IR. Moreover they were tested in a gas permeation set-up to determine the hydrogen and nitrogen permeability and selectivity. Roughness and porosity of original PSS supports were reduced after the incorporation of all types of silica layers, mainly for silicalite-1. As a consequence, the palladium deposition by electroless plating was clearly influenced by the feature of the intermediate layer incorporated. A defect free thin palladium layer with a thickness of ca. 5 μm over the support modified with silicalite-1 was obtained, showing a permeance of 1.423·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 and a complete ideal permselectivity of hydrogen.     

High hydrogen storage ability of a decorated g-C3N4 monolayer decorated with both Mg and Li: A density functional theory (DFT) study

In this work, the hydrogen storage properties of a g-C₃N₄ monolayer decorated with both Mg and Li were thoroughly investigated by performing density functional theory (DFT) calculations. Along these lines, the projected densities of states (PDOS) and the Bader Charge analysis showed that both Mg and Li atoms can transfer their electronic charges to the g-C₃N₄ monolayer. Interestingly, the latter is transformed from a semiconductor material to a metallic conductor configuration, while a local electric field is formed around it. On top of that, the formed local electric field polarized hydrogen molecules and as a result, led to an enhanced hydrogen adsorption ability. Mg atoms have more outmost electrons, and more charges can be transferred to the monolayer, which leads to the creation of a stronger local electric field to adsorb an elevated number of hydrogen molecules than Li atoms. On the other hand, Li atoms are lighter, more active and easier to lose outmost electrons than Mg atoms. By considering these advantages, a g-C₃N₄ monolayer decorated with one unit of both Mg and Li was investigated, which has the ability to adsorb 10 hydrogen molecules, leading thus to a high hydrogen storage capacity of 10.01 wt %. Our work paves the way for the development of novel material configurations for improved hydrogen storage applications.     

The effect of mixture gas on hydrogen permeation through a palladium membrane: Experimental study and theoretical approach

Hydrogen permeation through a palladium membrane has been measured in the presence of several gases, such as CO, _N2${\mathrm{N}}_2$, _CO2${\mathrm{CO}}_2$, and Ar, both in the feed side and in the shell side of the (membrane) module. It has been found that CO molecules, remarkably inhibit hydrogen permeation. In particular, in the presence of carbon monoxide the permeation decreases with two different slopes: (I) for low CO concentrations, the hydrogen permeation decreases quickly (surface effects), whereas (II) for higher ones it decreases smoothly (dilute effect). Permeation of hydrogen, in the presence of the other gases, i.e. _N2${\mathrm{N}}_2$, _CO2${\mathrm{CO}}_2$ and Ar, always decreases with the same slope (dilute effect). In order to describe the CO inhibition, a theoretical investigation has been proposed. In particular, the framework of the Density Functional Theory has been used. CO and _N2${\mathrm{N}}_2$ Density Functional full optimisations on palladium clusters show that CO and _N2${\mathrm{N}}_2$ molecules present two minima on the cluster surfaces with bond lengths of 2.0 and 3.8 Å, respectively. The CO minima are much stable than _N2${\mathrm{N}}_2$ minima, resulting in a surface effect on the hydrogen permeation through the membrane.     

Some approach to possible atmospheric impacts of a hydrogen energy system in the light of the geological past and present-day

Hydrogen has a considerable potential for becoming a major factor in speeding the transition of our carbon-based global energy economy ultimately to a clean, renewable and sustainable economy. The development of hydrogen production, transportation-storage and utilization technologies can play a central role in addressing growing concerns over carbon emissions and climate change, as well as the future availability and security of energy supply. However the widespread use of hydrogen may have unknown environmental effect due to increased anthropogenic emissions of molecular hydrogen and other gases to the atmosphere, through production, transportation-storage and utilization processes. It is recognized that hydrogen participates in stratospheric chemical cycles of H₂O and various greenhouse gases, and a substantial increase in its concentration might lead to changes in equilibrium concentration of constituent components of the stratosphere. More accurate modeling of the stratospheric processes as well as better understanding of several other factors such as hydrogen uptake in soil and its effect on microbial communities is required to assess potential adverse effects of hydrogen economy. It is critical for us to understand the potential adverse effect of widespread use of hydrogen and take necessary actions to understand and prevent its possible environmental impacts.     

Efficient hydrogen production from aqueous methanol in a PEM electrolyzer with porous metal flow field: Influence of PTFE treatment of the anode gas diffusion layer

In a proton exchange membrane (PEM) methanol electrolyzer, the even supply of reactant to and the smooth removal of carbon dioxide from the anode are very important in order to achieve a high hydrogen production performance. An appropriate design of flow field and gas diffusion layer (GDL) is a key factor in satisfying the above requirements. Previous research has shown that hydrogen production performance of the PEM methanol electrolyzer cell was largely improved with a porous flow field made of sintered spherical metal powder compared with a conventional groove type flow field. Based on this improvement, the current study investigated the influence of polytetrafluoroethylene (PTFE) treatment of the anode GDL on hydrogen production performance of the PEM methanol electrolyzer with porous metal flow fields. Influences of operating conditions such as methanol concentration and cell temperature with the flow field were also investigated.