Leakage Mechanism Research Articles

Molecular mechanisms of hydrogen leakage and blockage in kaolinite nano-cracks for underground hydrogen storage

Underground H2 storage in saline aquifers is critical for advancing the global energy transition through large-scale H2 utilization. However, cyclic stress-induced nano-cracks in caprocks may lead to leakage due to the small size and high diffusivity of H2. This study employed molecular dynamics simulations exploring the occurrence states of H2 and H2O near kaolinite surfaces, particularly focusing on H2 leakage when a nano-crack formed. We examined the effects of basal surfaces (gibbsite and siloxane), water content, and cushion gases (CH4 and CO2). In gibbsite aquifers, H2O formed adsorption layers; while in siloxane aquifers, it appeared as droplets or bridges. Upon nano-crack formation, initial H2 leakage occurred but halted once a critical number of H2O blocked the crack. H2 leakage was generally higher in siloxane than in gibbsite aquifers, except at low water content. Increased water content significantly reduced H2 leakage in gibbsite aquifers by rapidly achieving the critical H2O number, whereas the effect in siloxane aquifers depended on H2O distribution. Cushion gases effectively mitigated H2 leakage. CO2 outperformed CH4 in gibbsite aquifers, while their effects in siloxane aquifers varied based on H2O distribution. CH4 reduced leakage by hindering initial H2 entry into the crack, while CO2 not only impeded initial H2 entry but also assisted H2O in blocking the crack. Our analysis of density distributions, leakage dynamics, molecular configurations, and excess chemical potentials provides insights into H2 leakage and blockage mechanisms in aqueous environments near caprock minerals, facilitating the evaluation of H2 storage feasibility in saline aquifers.

Investigation of the effects of temperature cycling on the leakage mechanism of Through-Silicon Via (TSV) insulation layer

Investigation of the effects of temperature cycling on the leakage mechanism of Through-Silicon Via (TSV) insulation layer

Research on the mechanism and prediction model of gas leakage and diffusion from shallow-buried natural gas pipelines

As a crucial component of urban lifeline projects, shallow-buried gas pipelines pose a significant threat to society and people's lives, as well as property in the event of a leakage accident. To investigate the diffusion mechanism of gas leakage out of pipelines, the CFD method is employed to establish a validated numerical model for gas diffusion in backfilled soil. The effects of operating pressure, burial depth, leakage direction of pipelines, and soil resistance coefficient were discussed. The calculated results indicate that the numerical model can accurately predicte the diffusion process and the resistance coefficient of methane in soil-sand, loam, and clay-based. It was found that the burial depth affects the speed of gas diffusion to the soil surface but has little impacts on the concentration distribution range. The diffusion process in the same type of backfilled soil was found very similar under varying pipeline operating pressures, though the pipeline pressure significantly impacts the diffusion range. The shape of the leaked gas cloud in the soil is affected by soil resistance, leak direction, and air buoyancy. A new diffusion model for methane leaking in soil was proposed by introducing two time-related concentration adjustment parameters to the existing natural gas diffusion model. The average error between the calculated results of the proposed diffusion model and the established numerical model was found to be within 10%.

Modeling and Analysis of Internal Leakage Characteristics of the Internal Curve Motor by a CFD-Based Method

Internal curve motors (ICMs) are used in construction and port machinery owing to their low speed and strong torque. The internal leakage of an ICM has a direct impact on its working performance; however, research on the internal leakage of ICMs is unclear. A method, based on the Computational Fluid Dynamics (CFD) transient simulation of an ICM, for obtaining the transient pressure in the plunger chamber and combining the mathematical model of internal leakage is calculated, and the internal leakage is proposed. We one-factor analyzed the internal leakage of the ICM and the effect of the valve pair and plunger pair leakage, and conducted multifactor analysis on the effect of the interaction between those two factors on the internal leakage of the ICM. The results show that the internal leakage mechanisms affecting the ICM were, in descending order of impact, the inlet pressure, oil temperature, and rotational speed, and a significant interaction existed between the inlet pressure and oil temperature, whereas the influence of rotational speed was not significant.

Triple extended coprime array for single‐snapshot DoA estimation

AbstractThe direction‐of‐arrival (DoA) estimation methods based on coprime array (CA) largely rely on having a sufficient number of snapshots. However, under single‐snapshot conditions typical of vehicle‐mounted imaging radar, CA‐based DoA estimation often suffers from ambiguity leakage, resulting in significant degradation in performance. This paper thoroughly analyses the mechanism of ambiguity leakage in CA by re‐deriving the covariance matrix model under single‐snapshot conditions. To suppress the ambiguity leakage, a triple extended coprime array composed of three pairwise coprime sub‐arrays enhanced coprime constraint is designed. Building on this design, a DoA estimation algorithm based on an iterative adaptive approach is proposed. By leveraging the power spectrum distribution from iterative adaptive approach, a reduced‐noise signal is constructed by retaining only the high‐energy components. Next, the noise subspace using a multi‐stage Wiener filter, and finally, achieve super‐resolution DoA estimation through multiple signal classification spectrum analysis.

Study on the leakage mechanism of sealing with hyperelastic rough surfaces based on iterative algorithm

Abstract The sealing structures, found in various equipment used in daily life, industry, and the military, play roles in preventing leaks, contamination, and toxic gases. This study focuses on the sealing interface of hyperelastic rough surface, employing an iterative algorithm to calculate the leakage process under fluid action and determine the critical leakage pressure. By substituting the fluid load on the sealing interface before leakage with a uniformly distributed pressure, this algorithm accurately identifies the boundaries of fluid and sealing contact regions through continuous iteration. Consequently, it solves the sealing interface state under a certain pressure and incrementally increases the hydrostatic pressure to obtain the critical leakage pressure. This research visualizes the sealing leakage process and determines the critical leakage pressure of the sealing interface, offering practical value for engineering applications and providing guidance for the design and manufacturing methods of sealing components.

Air leakage mechanism and hole sealing technology in directional long-drilled perimeter rock-borehole composite fissures: for gas enrichment in varying coal-seam thickness change areas

The issue of gas enrichment in the tectonic zone of coal seams, which poses significant threats to coal mine safety and leads to gas disasters, is primarily addressed through borehole extraction. The quality of this extraction is notably influenced by air leakage and sealing technologies used during drilling. To tackle the problem of gas leakage in directional long boreholes within the floor, a composite fissure leakage model for the surrounding rock and borehole is developed. This model inverts the characteristics of coal seam thickness variations and abnormal gas enrichment through heterogeneous geostatistical modeling. It enables the quantitative characterization of the air leakage mechanism in directional long boreholes of the bottom plate and proposes an effective sealing process. Due to damage and disturbance, fissures and irregular plastic zones form around the excavated roadway, which are major contributors to air leakage. Over time, the air content in the coal and rock seams gradually increases while the gas content and concentration decrease continuously. Compared to the polyurethane "two plugs and one injection" sealing process, the multi-stage grouting and sealing process provides a more stable gas extraction concentration and flow rate in the sealed drill holes. This process effectively seals the fissure zones of the roadway, reduces air leakage from the boreholes, and improves gas extraction concentration.

Research on Natural Gas Leakage and Explosion Mechanisms in a Container House

As unconventional building structures, container houses are now widely used in urban tourism to create characteristic buildings. Nowadays, natural gas accidents occur frequently in cities and towns; however, the development of laws and influencing factors of natural gas accidents in container buildings have rarely been studied. In this paper, a natural gas explosion test was carried out in an ordinary container house, and a numerical simulation was carried out according to the test results. The influence of methane proportion, ignition position, pressure-relief area, and pressure-relief intensity on the explosion load was analyzed. Research shows that natural gas will gather from top to bottom during the process of leakage and diffusion, and vertical stratification will occur. The most unfavorable working condition is 9.5% methane. Using the roof of the container house as a pressure-relief panel can effectively control the influence range of natural gas explosion accidents and help reduce accident losses. It is suggested that the stacking of container buildings should be reduced as much as possible, and the roof strength should be weakened to ensure structural safety. The research results have certain reference values for the disaster prevention and reduction design of urban characteristic buildings.

Experimental investigation of natural gas leakage and dispersion characteristics in utility tunnels under the effects of real facility layout and forced ventilation

Natural gas leakage occurring in underground utility tunnels usually poses a significant threat to public safety. In order to prevent unexpected fires and explosions, the evolution mechanism of natural gas leakage and dispersion in utility tunnels is urgently needed. In this study, an experimental apparatus was built to facilitate the understanding of leakage and dispersion dynamics in utility tunnels. Methane with a purity of 99.9% is used as a surrogate for natural gas. A schlieren imaging system with a Z-shaped optical path was designed to visualize the high-speed gas jet. The concentration distribution, alarm time, dilution efficiency, and gas jet image were analyzed under the effect of various facility layouts, ventilation, and leakage rates. The results show that the gas leakage and dispersion process can be divided into three zones: upwind zone, leak zone, and downwind zone, characterized by complicated airflow collision, high-speed get jets, and stable dilution dispersion respectively. Scenario analysis highlights the significance of key facilities, such as cable brackets, in experimental and numerical modeling due to their impact on dispersion trajectories. Higher ventilation rates prove beneficial in reducing peak concentration, hazardous areas, and enhancing purge efficiency. Conversely, higher leakage rates exacerbate the likelihood and severity of gas explosions. Alarm time exhibits a V-shaped distribution relative to the leak point, while purge time correlates positively with sensor positions. These findings are of practical importance in enhancing quantitative risk assessment and designing mitigation strategies for gas leakage accidents, which helps to improve the safety-risk-control capabilities of utility tunnels.

Improved p-GaN/AlGaN/GaN HEMTs with magnetronsputtered AlN cap layer

In this paper, a low temperature sputtered AlN cap-layer p-GaN HEMT with high gate breakdown and improved reliability is realized. XPS test shows that the valence band offset of p-GaN and low-temperature magnetron sputtered AlN is 1.2 eV, which successfully suppresses the gate leakage current and greatly improves the gate reliability. Low capacitance–voltage hysteresis and small pulsed threshold voltage shift predict good AlN/p-GaN interface quality. The threshold voltage of the AlN/p-GaN HEMT is improved from 0.61 V to 0.82 V compared to the conventional p-GaN HEMT with tungsten Schottky gate (W/p-GaN HEMT), the DIBL decrease from 34.4 mV/V in W/p-GaN HEMT to 1.1 mV/V in AlN/p-GaN HEMT. The gate forward and reverse leakage is significantly suppressed, and the gate forward breakdown voltage is improved to 17 V. The gate operating range is improved from 7 V to 12 V, and the ID/IG under saturation state is improved from 104 to 107. In addition, a smaller on-resistance of 67.5 Ω·mm was obtained, which is 15.3 % lower than that of the W/p-GaN HEMT, minimizing on-state loss. The gate leakage mechanism of the AlN/p-GaN HEMT is mainly dominated by the PF emission in the medium gate voltage range. Based on this leakage mechanism, the maximum forward VG for a ten-year lifetime was extracted as 6.8 V at room temperature at a failure level of 63.2 % for the AlN/p-GaN HEMT, while this value for W/p-GaN HEMT is 5.4 V. In addition, the AlN cap layer attenuates the depletion region of metal/p-GaN by the gate Schottky metal, which keeps the GaN channel better depleted, thus keeping a higher off-state breakdown voltage. These results demonstrate the good potential of magnetron sputtering AlN as a low-cost, methodologically simple growth method for the commercial use of p-GaN HEMTs.

Modeling and Validation of the Sealing Performance of High-Pressure Vane Rotary Actuator

The EHRA (Electro-Hydraulic Rotary Actuator), using a vane rotary actuator, has the advantages of a high torque density and integration and is expected to become a joint actuator for robots. This research focuses on the sealing characteristics of various parts of a vane rotary actuator. The average Reynolds equation was used to analyze the leakage characteristics at the gap. A detailed theoretical analysis was conducted on the internal leakage mechanism of a vane rotary actuator using an X-ring as the dynamic seal for the rotor vane. According to the path of internal leakage, different sealing forms are considered as a series or parallel, and the Newton iteration method is used to obtain the total internal leakage characteristics of a vane rotary actuator. It was also considered that the deformation of the vane rotary actuator caused a thicker gap, leading to an increase in internal leakage. The calculation results are consistent with the experimental data. The analysis results indicate that when estimating the internal leakage of a vane rotary actuator, it is necessary to take the pressure of the high-pressure chamber and output shaft position as inputs. This research provides a reference for an analysis of the method of internal leakage for vane rotary actuators. It provides theoretical support for designing a vane rotary actuator with more minor internal leakage and a higher volumetric efficiency.

Investigation of the leakage mechanism in solar-blind AlGaN p-i-n photodetector at high reverse bias

The leakage mechanism of solar-blind AlGaN p-i-n photodetectors has been investigated. By studying the temperature-dependent I–V curves, we determined that Poole–Frenkel emission is the main source of the leakage current, and the corresponding trap energy level is 0.61 eV. Cathodoluminescence measurement demonstrates that the leakage current of the device may be related to the deep-level traps in the p-AlGaN layer. An analysis of deep-level transient spectroscopy testing results for p-AlGaN suggests that nitrogen vacancies formed during the epitaxial growth of high Al-content p-AlGaN act as electron traps. The trap potential energy decreases at high reverse bias voltage, making trapped electrons easier to escape, which increases the leakage current.

Adaptive Robust Autonomous Vehicle Driving Strategy in Transportation Systems: Gated Leakage Mechanism Designs

Adaptive Robust Autonomous Vehicle Driving Strategy in Transportation Systems: Gated Leakage Mechanism Designs

An innovative sludge-derived capsule for self-healing cementitious materials

An innovative eco-efficient capsule utilizing drinking water treatment sludge (DWTS) as a healing agent for concrete crack sealing was developed. In this study, the core materials comprised a mix of DWTS and calcium hydroxide, granulated by poly (ethylene glycol). A non-toxic polymer, Ethyl cellulose (EC), is applied as the protective shell material. The morphology, internal structure, and leakage mechanism of capsules, self-healing performance of cracked mortars and the composition of resulting healing products were assessed. Obtained results indicated that EC uniformly covered the spherical core material following the designed coating procedures. The main elements released from the capsules were Ca, Al and Si after dissolution of polyethylene glycol (PEG), which would contribute to pozzolanic reactions inside the matrix. Cracks with an initial width of 400 μm were completely healed after 7 days of curing. Such a healing process also led to an 73% enhancement in compressive strength at a healing age of 28 days. The water tightness of capsule-based samples improved by more than 90% in the first 7 days, compared to only 10% in control samples. The predominant healing products were calcium carbonate in the form of calcite, and some content of aluminium-bearing phases derived from the pozzolanic reaction of DWTS.

Fast switching Ga2O3 Schottky barrier power diode with beveled-mesa and BaTiO3 field plate edge termination

Power devices rely on ideal edge termination to suppress the electric field crowding and avoid premature breakdown before the material's critical field is reached. In this work, a hybrid electric field management configuration, featuring the combination of beveled-mesa (BM) termination and high-k oxide BaTiO3 field plate (FP), was implemented in Ga2O3 Schottky barrier diodes (SBDs). This BMFP-SBD realizes a breakdown voltage (BV) of 1.7 kV with extremely low reverse leakage current, outperforming the BM terminated SBD with BV of 0.64 kV and bare SBD with BV of 0.22 kV. Based on the temperature-dependent reverse characteristics, the dominant leakage mechanism transforms from Poole–Frenkel (P–F) emission in BM-SBD to variable-range-hopping (VRH) in BMFP-SBD at high bias. In particular, under switching conditions of di/dt up to 420 A/μs, the BMFP-SBD exhibits superior dynamic switching characteristics with a short reverse recovery time of 10.1 ns, which are comparable with those in advanced commercial SiC SBDs. These findings underscore the potential of Ga2O3 SBD enabled by BM and high-k FP edge termination for high-speed and high-voltage power electronics applications.

Dynamic Models of Mechanical Seals for Turbomachinery Application

One of the primary causes of mechanical face seal failure is rotor vibration. Traditional dynamic seal models often cannot fully explain failure mechanisms. The dynamic models of seals proposed in this paper, including those developed by the authors, are valuable for predicting seal dynamics during operation in specific turbomachinery and for explaining the causes of seal failure. The single-mass dynamic model is suitable for analyzing the dynamics of contact mechanical face seals and simply designed dry gas seals. The two-mass dynamic model is used to investigate the operational dynamics processes of classical dry gas seals under complex loading conditions. The three-mass dynamic model is used to study various complex types of mechanical face seals. This model can determine the normal operating condition range and explain leakage mechanisms in the presence of excessive rotor vibrations.

Tangential contact modeling to seal considering elastic-plastic for lubrication transition mechanism

Researches on the reciprocating seals lubrication under elastic-hydrodynamic lubrication (EHL) are mature, and leakage of failure criterion has been described with Couette flow for more than 30 years, which could not reflect to leakage mechanism in multiscale. Thus, it is necessary to explore seal leakage failure to focus on micro convex bodies of asperities model under contact pressure and cycle tangential friction stress in mixed lubrication. This is because convex bodies behaviors determine sealing effect and lubrication behaviors in microscale with subjecting to the dominant pressure. Interaction between convex bodies fatigue hysteresis curve and elastic-plastic strain are also calculated to explore sealing effect with leakage rate mechanism. We then design water seal at high pressure of 100 MPa with the speed of 0.1–1 m/s and medium temperature from 5 ℃ to 40 ℃. IWAN model of the convex bodies are calculated. Probability density function and Jenkin’s elements critical slip displacement are obtained. Convex bodies of radial and tangential deformation are also calculated through loading of contact pressure and friction stress with cycle strength coefficient to obtain seal fatigue lifespan. Ratio to seal stick and slip friction is calculated for evaluating the loading boundary. Seal leakage failure mechanism with fatigue characteristics is illustrated with macro lubrication parameters and micro convex bodies mechanics performance.

An review of research on liquid hydrogen leakage: regarding China’s hydrogen refueling stations

Hydrogen is regarded as the premier energy source for future sustainability and renewability. However, its distinct physicochemical properties render it prone to explosions in the event of a leak. Therefore, there is a need for more comprehensive research dealing with hydrogen leakage, explosion scenarios, and risk assessment. This paper provides an overview of the current hydrogen policies adopted in China. It reviews the processes of hydrogen refueling station construction and the thermophysical mechanisms of liquid hydrogen leakage. In this regard, the effects of various factors, including leakage rate, leakage time, leakage hole size, wind direction and speed, and building location, on the hydrogen leakage rate are analyzed and evaluated. Additionally, the impacts of different factors on hydrogen explosion overpressure are reported, including hydrogen concentration, wind speed, obstacles, and ignition position, in addition to the current applications of quantitative risk assessment methods in hydrogen refueling stations. Finally, the limitations of current research on liquid hydrogen leakage and explosion accidents are highlighted, along with the shortcomings of current risk assessment methods for liquid hydrogen refueling stations.

Leakage current in GaN-on-GaN vertical GaN SBDs grown by HVPE on native GaN substrates

This study investigates leakage mechanisms in vertical GaN-on-GaN Schottky barrier diodes (SBDs) and demonstrates effective mitigation strategies. The fabricated devices exhibit low reverse leakage current (1 × 10−5 A/cm2 at −200 V) and a high Ion/Ioff ratio (∼1010), surpassing the performance of GaN SBDs on foreign substrates. We elucidate dominant leakage mechanisms—thermionic emission, Poole–Frenkel emission, and variable-range hopping—and their evolution with temperature and bias. Optimized fabrication processes, including defect etching and a novel dual-layer passivation technique, achieve over a 1000-fold reduction in leakage current.

CH4 hydrate dissociation and CH4 leakage characteristics: Insights from laboratory investigation based on stratified environment reconstruction of natural gas hydrate reservoir

Submarine natural gas hydrates (NGHs) are one of the largest methane reservoirs on Earth, offering huge potential as an alternative energy source and serving as a crucial global carbon sink. However, the substantial risk of methane leakage during NGH development seriously threatens marine and global ecological and environmental safety, presenting a major challenge for commercial NGH exploitation. Focusing on the unknown leakage mechanisms, this study employed a new simulation device to construct a stratified environment and to investigate the characteristics of hydrate dissociation and methane leakage during depressurization production, under conditions of varied fracturing in overlying sediment. A movable module was used to dynamically isolate and connect the hydrate reservoir with the overlying layer. The results showed that the intrusion of overlying water decelerated the reservoir depressurization rate, leading to a mass of hydrate reformation. The invasion locations and flow paths of the overlying water were influenced by the fracture scale of the overlying sediment. Benefiting from the additional sensible heat and reservoir space occupation of the overlying water in the later production stages, the methane recovery ratio in the fracture-containing systems were not significantly affected. However, the leakage methane increased as fracture channels enlarged, reaching up to 9.90 % of the total methane content in the hydrate reservoir. The leakage mechanism primarily involved local overpressure, buoyancy effects, and diffusion. The research, for the first time, experimentally revealed the response relationship between methane leakage and hydrate dissociation, providing foundational data and theoretical support for the safe and efficient NGH development.