Small Leakage Rate Research Articles

Effects of sand size on spread and heat transfer of continuous spill fires with small leakage rates

Effects of sand size on spread and heat transfer of continuous spill fires with small leakage rates

Leakage and diffusion of high-pressure gas pipeline in soil and atmosphere: experimental and numerical study

ABSTRACT Personal safety and environmental issues, such as fires and explosions, have climbed to the top of the list of concerns due to the rupture of a high-pressure gas pipeline. Analysis of the diffusion characteristics of methane leaks in soil and air is essential for engineering maintenance and the prevention of secondary mishaps. The primary contribution of this paper is the design and establishment of a full-scale experimental system to simulate small-hole leakage of high-pressure gas pipeline in order to observe the leakage and diffusion behavior of methane in soil and atmosphere under various leakage pore sizes and pressures. The results show that, near the leakage hole, the high-pressure jet dominates the action, whereas near the surface, lateral diffusion and accumulation dominate for an extended period of time. When the diffusion reaches a stable state, the vertical and horizontal diffusion distances are 0.76 m and 1.05 m, respectively, and the maximum temperature difference at the leakage hole is 8.7°C; Under the conditions of leakage holes of 0.5 mm, 1.0 mm, and 1.5 mm, the surface leakage radii are 0.4 m, 0.8 m, and 1.4 m, respectively. The leakage aperture is the main factor affecting the diffusion of methane in soil; A small hole leakage rate model for high-pressure gas pipelines was established based on experimental data, with an average error of 9%; The response time and steady time in the process of methane concentration growth have an exponential relationship with horizontal distance from the leakage hole and a power function relationship with vertical distance and leakage rate. The average relative errors of the calculation formula are 16% and 12%, respectively. This work can provide a basis for the hazard assessment of small hole leakage and diffusion in buried gas pipelines, and also provide data support for the theoretical and numerical models of high-pressure gas flow in soil and atmosphere.

Characterization of carbon dioxide leakage process along faults in the laboratory

It is important to understand the process of multiphase carbon dioxide (CO 2 ) leakage in faults for the risk assessment of carbon capture and storage (CCS). To quantitatively characterize the CO 2 leakage process in the fault, pressure sensors, fiber Bragg grating (FBG) temperature and strain sensors were simultaneously used to monitor CO 2 leakage in the fault. Ten experiments were carried out, including five groups of gaseous CO 2 leakage tests with initial pressures of 1–5 MPa and five groups of liquid CO 2 leakage tests with initial pressures of 6–10 MPa. The results indicate that when liquid CO 2 leaked with an initial pressure of 7–10 MPa, the pressure and temperature of CO 2 dropped rapidly in the first few seconds and then remained unchanged. The behavior that CO 2 continues to leak while maintaining temperature and pressure unchanged is defined as “temporary pseudo-sealing (TPS)” behavior, which continues for the first 1/3 of the leakage period. However, this TPS behavior did not occur in gaseous CO 2 leakage. If only the pressure and temperature data were used to evaluate whether CO 2 leakage occurred, we would misjudge the risk of leakage in CCS projects during the TPS period. The causes and conditions of TPS behavior were further studied experimentally. The results show that: (1) TPS behavior is caused by the phase transition energy generated when liquid CO 2 leaks. (2) The condition for TPS behavior is a small leak aperture (0.2 mm). Only a small leakage rate can make the phase transition energy and pressure change from a dynamic equilibrium, and (3) The compression zone caused by the Bernoulli effect and fault “barrier” could reduce the CO 2 leakage rate and further promote the occurrence of TPS behavior. This study provides technical and theoretical support for the quantitative characterization of the CO 2 leakage process in faults of CCS projects.

Graphene perfect absorber with loss adaptive Q-factor control function enabled by quasi-bound states in the continuum

Numerous device structures have been proposed for perfect absorption in monolayer graphene under single-sided illumination, all of which requires the critical coupling condition, i.e., the balance between the loss of graphene and the leakage rate of the device. However, due to the difficulty of the precise control of the quality of synthesized graphene and unwanted doping in graphene transferred to the substrate, the loss of graphene is rather unpredictable, so that the perfect absorption is quite difficult to achieve in practice. To solve this problem, we designed a novel perfect absorber structure with a loss adaptive leakage rate control function enabled by the quasi-bound states in the continuum (BIC) and numerically demonstrated its performance. Our designed device is based on a slab-waveguide grating supporting both the quasi-BIC and the guided-mode resonance (GMR); the quasi-BIC with an adjustable leakage rate controlled by an incident angle is responsible for absorption, while the GMR works as an internal mirror. Since the proposed device scheme can have an arbitrarily small leakage rate, it can be used to implement a perfect absorber for any kind of ultrathin absorbing media. Due to the simple structure avoiding an external reflector, the device is easy to fabricate.

Synergistic enhancement of thermal conductivity for expanded graphite and carbon fiber in paraffin/EVA form-stable phase change materials

Thermally conductive form-stable phase change materials (FSPCMs) were prepared by using ethylene-vinyl acetate (EVA), paraffin, expanded graphite (EG) and carbon fiber (CF) as row materials. Two-dimensional EG and one-dimensional CF were used as thermally conductive fillers. Paraffin and EVA were phase change material (PCM) and supporting material, respectively. Differential scanning calorimetry (DSC) and leakage rate testing results indicated that FSPCMs owned the melting temperature of 45.63°C and the latent heat of 167.4J/g. The prepared material had a small leakage rate which was less than 2%. Scanning electron microscope (SEM) results shown that EG and CF possessed excellent compatibility in FSPCMs. In-situ X-ray diffraction (XRD) tests demonstrated that the crystal behaviors of paraffin and EVA were changed with the phase transformation. Thermal conductivity results shown that thermal conductivity of FSPCMs in horizontal orientation was higher than that in longitudinal orientation. EG and CF have synergistic enhancement to thermal conductivity of FSPCMs.

Analysis of Activated Air Following High Yield Shots in the NIF

During the ignition experimental campaign, the National Ignition Facility (NIF) is expected to perform shots with varying fusion yield (up to 20 MJ or 7.1 x 1018 neutrons per shot) and a maximum annual yield of 1200 MJ. A detailed MCNP model of the Target Bay (TB) and the two switchyards (SY) has been developed to estimate the post-shot radiation environment inside the facility. During D-T shots, a pulse of 14.1 MeV neutrons streaming outside the Target Chamber (TC) will activate the air present inside the TB and the argon gas inside the laser tubes. Smaller levels of activity are also generated in the SY air and in the argon portion of the SY laser beam path. The activated TB air will be mixed with fresh air from the Operations Support Building (OSB) before release through the stack. Flow of activated air from the Target Bay is controlled by the heating, ventilating, and air conditioning (HVAC) system. 16N (T1/2 = 7.13 s) dominates the radiation levels during the first minute following the shot. It is expected that 16N will decay away during the confinement time before releasing the TB air through the stack. The other major contributors are 13N (T1/2 = 9.97 min) and 41Ar (T1/2 = 1.83 h). In general a low dose rate of < 1 μSv/h is expected near the stack during the first few hours following a 20 MJ shot. The amount of activated Target Bay air released through the stack is very small and does not pose significant hazard to personnel or the environment. In the mean time, due to a very small leakage rate out of the laser tubes, the activated argon gas decays within the tubes and any resulting release to the environment is insignificant.

Surface geochemical measurements applied to monitoring, verification, and accounting of leakage from sequestration projects

A detailed study of [Formula: see text] and [Formula: see text] surface fluxes, shallow soil gas composition, 10-m hole soil gas composition was made at Rangely, Colorado, Teapot Dome, Wyoming, USA, and the results of geochemical verification measurements at Weyburn, Saskatchewan, Canada. Summer and winter soil gas and gas flux measurements were made at Rangely, and winter only at Teapot Dome. The objectives were to determine if leakage of [Formula: see text] and/or [Formula: see text] could be detected in the overpressured Rangely and the underpressured Teapot Dome systems. At Weyburn, the objective was the determination of the presence or absence of an alleged leak. Seasonal surface [Formula: see text] fluxes at Rangely were similar at on-field locations and an off-field control area. Methane fluxes were much higher at on-field locations than in the control area, suggesting a reservoir source. Seasonal differences in [Formula: see text] fluxes suggested methanotrophic oxidation was occurring in the soils. Shallow soil gas concentration measurements of [Formula: see text] were similar at a 100-cm depth, on-field and in the control area. Methane soil gas concentrations were higher on-field than in the control area; summer and winter. These data were used to select locations with and without evidence for seepage allowing nested sampling up to a 10-m depth. More complex chemical and isotopic measurements were made in 10-m holes at Rangely and Teapot Dome. Methanotrophy was operational at the active Rangely and the passive Teapot Dome systems. A small methane leakage rate of 400–700 tonnes [Formula: see text] and [Formula: see text] of [Formula: see text] tonnes [Formula: see text] were determined at Rangely, and rates near zero at Teapot Dome. Inert gases, carbon-containing gases, as well as isotopic ratios supported the presence of pathways at geochemically anomalous locations at Teapot Dome. Measurements of soil gas and inert gas isotopes in shallow groundwater by other authors at Weyburn, Saskatchewan, found no evidence of leakage.

Effectiveness of subsurface pressure monitoring for brine leakage detection in an uncertain CO2 sequestration system

This work evaluates the detection sensitivity of deep subsurface pressure monitoring within an uncertain carbon dioxide sequestration system by linking the output of an analytical reduced-order model and first-order uncertainty analysis. A baseline (non-leaky) modeling run was compared against 10 different leakage scenarios, where the cap rock permeability was increased by factors of 2–100 (cap rock permeability from 10−3 to 10−1 millidarcy). The uncertainty variance outputs were used to develop percentile estimates and detection sensitivity for pressure throughout the deep subsurface as a function of space (lateral distance from the injection wells and vertical orientation within the reservoir) and time (years since injection), or P(x, z, t). Conditional probabilities were computed for combinations of x, z, and t, which were then used to generate power curves for detecting leakage scenarios. The results suggest that measurements of the absolute change in pressure within the target injection aquifer would not be able to distinguish small leakage rates (i.e., less than 50 × baseline) from baseline conditions, and that only large leakage rates (i.e., >100 × baseline) would be discriminated with sufficient statistical power (>99 %). Combining measurements, for example by taking the ratio of formation pressure in Aquifer 2/Aquifer 1, provides better statistical power for distinguishing smaller leakage rates at earlier times in the injection program. Detection sensitivity for pressure is a function of space and time. Therefore, design of an adequate monitoring network for subsurface pressure should account for this space–time variability to ensure that the monitoring system performs to the necessary design criteria, e.g., specific false-negative and false-positive rates.

Pervaporation studies of n-hexane, benzene, mesitylene and their mixtures on zeolitic imidazolate framework-8 membranes

The metal–organic framework (MOF) ZIF-8 (ZIF-8=zeolitic imidazolate framework-8) was evaluated as molecular sieve membrane in the pervaporation of the two liquid mixtures n-hexane/benzene and n-hexane/mesitylene. Though it is known from permeation studies of light gases that ZIF-8 membranes show no sharp separation cut-off at the estimated crystallographic pore size of 3.4Å, highly branched or aromatic hydrocarbons>C5 could be expected therefore to become rejected by the ZIF-8 pores thus remaining in the retentate. However, the ZIF-8 membrane shows for n-hexane and benzene remarkable fluxes. Under consideration of the leakage of the apparatus, we can state that n-hexane and benzene can pass the ZIF-8 membrane. Benzene had a lower flux than n-hexane, whereas for mesitylene we could only observe a very small leakage rate through the O-ring gasket. Correspondingly, medium mixture separation factors have been found for the pervaporation separation of a liquid n-hexane/benzene mixture. Additional mixed gas hydrogen/methane separations, adsorption experiments and leak rate measurements were carried out to evaluate the results.

Modeling brine leakage to shallow aquifer through an open wellbore using T2WELL/ECO2N

The efficiency and sustainability of CO2 storage in deep saline formations depends on the integrity of the overlying caprocks. Existing oil and gas wells, which penetrate the formations, are potential leakage pathways. In this paper, T2WELL/ECO2N, a coupled wellbore–reservoir flow simulator of carbon dioxide and brine, is employed to analyze the effects of salinity and excess pore pressure (EPP) on brine leakage from an injection reservoir to a shallow fresh aquifer. The effectiveness of the Equivalent Porous Media (EPM) approach, a widely used approximation of wellbore flow in wellbore–reservoir simulations, is also evaluated. A hypothetical model is built to create test cases with EPP of 0.1MPa, 0.5MPa and 1.5MPa under low-, middle-, and high-salinity. The results show that a quasi-steady-state leakage rate will be quickly established if the EPP caused by CO2 injection is higher than the threshold EPP. However, the brine salinity has an important impact on the brine leakage rate including the threshold EPP below which no leakage occurs. The leakage rate decreases with the increase of the salinity whereas the threshold EPP increases with the increase of the salinity. For the same brine salinity, the quasi-steady-state leakage rate increases with the EPP nonlinearly. The leakage rate calculated by the EPM approach is very sensitive to the equivalent permeability of the wellbore, which however, is not an intrinsic parameter of a given wellbore–aquifer system. Although the EPM approach could reproduce the dynamic leakage rate reasonably well with a fitted permeability, it could over- or underestimates the leakage rate by orders in magnitude for the same system depending on whether the true leakage rate itself is smaller or larger than that of the fitting case due to changes in the salinity and/or the EPP through an abandoned well. The dependence of the equivalent permeability on the flow rate makes the EPM approach not to be a viable method for predicting wellbore leakage except for the cases with very small leakage rates.

Wastage and Self-Plugging by a Potential CO2 Ingress in a Supercritical CO2 Power Conversion System of an SFR

For a CO2 ingress accident into liquid sodium in a supercritical CO2 power conversion system coupled with a sodium-cooled fast reactor, we investigated two major design issues: i) a wastage phenomenon in regard to structural damage adjacent to the leaking position, and ii) potential channel plugging due to the formation of a particulate reaction product. In order to understand the factors affecting the occurrence of these issues, two kinds of experiments were carried out: a wastage effect test and a self-plugging test. All experimental conditions were chosen to reasonably represent the normal operating conditions and realistic design parameters of the reference plant. The test results indicate the absence of wastage, which will not lead to additional tube ruptures and damage propagation. In the current experiment, the self-plugging of PCHE channels only took place under two limited conditions: i) the sodium temperature is over 500°C and ii) the equivalent diameter of the crack opening is less than 1.5mm with a small leakage rate of far less than 1 g/s of CO2 ingress.

Atmospheric monitoring and verification technologies for CO 2 geosequestration

The paper describes various techniques for measuring emissions to the atmosphere from geologically stored carbon dioxide, from point, line and area sources at scales of metres to several kilometres. Flux chambers are suitable for measuring small leakage rates from sources at known locations but many samples are required because of large spatial heterogeneity in the fluxes. Micrometeorological eddy covariance, relaxed eddy accumulation and flux-gradient techniques are suitable for measuring leakage from large area sources, while integrated horizontal mass balance, tracer methods and plume dispersion approaches are applicable for line and point sources. Distinguishing between leakage signals and natural fluctuations in CO 2 concentrations due to biogenic sources pose significant challenges and the use of naturally occurring tracers such as CO 2 isotopologues or introduced tracers such as SF 6 added to the sequestered CO 2 will assist with this problem. Forward Lagrangian dispersion calculations showed that CO 2 concentrations 0–80 m downwind of a point source would be readily detectable above all natural variations for point sources >0.3 g CO 2 s −1 (about 10 tonnes of CO 2 per year). The inverse problem involves solving for the unknown emission rate from measured wind fields and down wind concentration perturbations. An optimum monitoring strategy for inverse analysis will require continuous measurements of CO 2 and tracer compounds upwind and downwind of the possible leak location, coupled with transport modelling to determine leakage fluxes, and to differentiate them from other sources. Computations using The air pollution model (TAPM) showed that expected perturbations in CO 2 concentrations at distances of several hundred metres from a leak of 32 g CO 2 s −1 (about 1000 tonnes CO 2 per year, or about 0.01% per year of a typical amount to be stored) will be detectable, but this anomaly will be very small compared to natural variations, thereby complicating the inverse analysis. While the techniques canvassed here have proven successful for measuring fluxes in other applications, none has yet been demonstrated for geosequestration. The next step is to test them in the field.

A micro-machined safety valve for power applications with improved sealing

A novel micro-safety valve for portable hydrogen fuel cells has been designed, fabricated and characterized. This device is intended to prevent over-pressure on the hydrogen side of the fuel cell. A careful study of its sealing properties has been conducted under conditions at which it is nearly open. The leakage rate depending on the size of the sealing surface and on the material of the gasket (fluorocarbon and parylene films) has been investigated using hydrogen gas. The experimental results show that small sealing surfaces lead to small leakage rates and that the parylene films are easily damaged, leading to important leakage rates. Moreover, it is shown that the resistance to flow of the device is diminished by reducing the width of the valve nozzle.

Investigation of leak detection method by means of measuring the pressure increment in vacuum

Leak detection by measuring the pressure increment in a vacuum has found wide application on pressure vessels, pipes and accessories. However, the reproducibility of the method and the effect of some secondary factors on the results of leak detection have not yet been satisfactorily studied and explained. In this paper, the leak detection method is discussed and the possibility of measuring small leakage rates outlined. Some factors influencing the results, especially the virtual leakage rate and test temperature, which may affect the accurate measurement of small leakage rates, are investigated in detail. In order to improve measurement accuracy, it is suggested that the evacuation time is prolonged and, if possible, the testing system is pre-heated, to eliminate the influence of the virtual leakage rate as far as possible. The research results indicate that both the variation of the ambient temperature and the inconsistency of the temperature of the testing system with that of the gas leaking into the system will introduce errors. Methods for correcting measured results are proposed.

Metrics to assess the mitigation of global warming by carbon capture and storage in the ocean and in geological reservoirs

Different metrics to assess mitigation of global warming by carbon capture and storage are discussed. The climatic impact of capturing 30% of the anthropogenic carbon emission and its storage in the ocean or in geological reservoir are evaluated for different stabilization scenarios using a reduced‐form carbon cycle‐climate model. The accumulated Global Warming Avoided (GWA) remains, after a ramp‐up during the first ∼50 years, in the range of 15 to 30% over the next millennium for deep ocean injection and for geological storage with annual leakage rates of up to about 0.001. For longer time scales, the GWA may approach zero or become negative for storage in a reservoir with even small leakage rates, accounting for the CO2 associated with the energy penalty for carbon capture. For an annual leakage rate of 0.01, surface air temperature becomes higher than in the absence of storage after three centuries only.

Sustainability of fission energy in future equilibrium society

The system of a fast reactor fed with natural uranium is discussed as a future sustainable energy producing system, concentrating especially on the waste problem. The following conclusions have been derived: 1. 1.|When the reprocessing with very small leakage rate can be employed, the conventional fast reactor has a potential to confine all actinides in the core. 2. 2.|The total toxicity of LLFPs is smaller but comparable to the toxicity of burned natural uranium with its daughters. 3. 3.|When the isotope separation is employed for each LLFP, whole LLFPs can be incinerated using the conventional fast reactor system with natural uranium. 4. 4.|When only the element separation is employed, the incineration of 107Pd should be given up even by employing several design changes, but its toxicity is only 0.0002 of the incinerated uranium toxicity.

Small Gas Leakage Rate Measuring and Monitoring System for Spent Fuel Transport/Storage Cask

A containment function of transport and/or storage casks of radioactive materials is essential to prevent the materials from being released excessively into the environment. It is not practical for containment tests to measure directly the radioactivity release so that gas volumetric leakage rates are usually assessed and gas pressure decrease or increase method is usually applied. As gas flow model for evaluation, the ISO standards has deleted the concept of choked flow which is adopted by ANSI N14.5. Provided that the choked flow is not adopted to the leakage rate evaluation, the criteria of the test should be severer, and a new leakage rate measuring system with high accuracy and reasonable measuring time is required. Transport casks are often inspected in a temporary cask-storage facility where simultaneous measurement of many casks is required. In a storage cask system, multiple casks are monitored on their containment function during a storage period, and the method for simultaneous monitoring at many points for long term is required. In this study, two kinds of small gas leakage rate measuring systems are developed. One is to measure gas leakage rates directly and is called “flow measuring system”, which can measure gas leakage rate of 10−4 to 10−2 cm3/s with high accuracy and short measuring time. The other is to measure the pressure decreasing rate and is called “pressure decreasing rate measuring system”, which can monitor the pressure change at many points simultaneously.

Small Gas Leakage Rate Measuring and Monitoring System for Spent Fuel Transport/Storage Cask.

A containment function of transport and/or storage casks of radioactive materials is essential to prevent the materials from being released excessively into the environment. It is not practical for containment tests to measure directly the radioactivity release so that gas volumetric leakage rates are usually assessed and gas pressure decrease or increase method is usually applied. As gas flow model for evaluation, the ISO standards has deleted the concept of choked flow which is adopted by ANSI N14.5. Provided that the choked flow is not adopted to the leakage rate evaluation, the criteria of the test should be severer, and a new leakage rate measuring system with high accuracy and reasonable measuring time is required. Transport casks are often inspected in a temporary cask-storage facility where simultaneous measurement of many casks is required. In a storage cask system, multiple casks are monitored on their containment function during a storage period, and the method for simultaneous monitoring at many points for long term is required. In this study, two kinds of small gas leakage rate measuring systems are developed. One is to measure gas leakage rates directly and is called “flow measuring system”, which can measure gas leakage rate of 10−4 to 10−2 cm3/s with high accuracy and short measuring time. The other is to measure the pressure decreasing rate and is called “pressure decreasing rate measuring system”, which can monitor the pressure change at many points simultaneously.

Double-disk structure for output coupling in microdisk lasers

We report our experiment on the use of a double-disk structure to couple light output from a microdisk laser which allows us to maintain a high Q value of the microdisk resonator. The small photon leakage rate from the lower lasing disk to the top waveguiding disk can be carefully controlled by choosing the distance between the two disks. Various structures can be fabricated on the top disk to couple the light out. In this letter, a simple opening in the top disk is used for output coupling.

Leakage of gas through concrete cracks

This paper aims at formulating the gas leakage rate through cracks in concrete walls. Leakage tests were carried out using eighteen specimens. Five specimens with a reinforcing bar and thirteen without were tested. The kind of fine aggregate and the size of the coarse aggregate were varied. Crushed gravel was used as the coarse aggregate. In order to examine the dispersion of the experimental results, four or five specimens with the same dimensions and of the same type of concrete were tested. The experimental results were formulated accurately by an isothermal compressible-flow equation for each identified crack. The two-dimensional Poiseuille-flow equation was also applied successfully for a small leakage rate. The dispersion of the test data from the same specimens, the influence of the aggregate and the effect of the reinforcing bar are discussed. It is concluded that the influence of the aggregate can be neglected and that the reinforcing bar reduces the leakage rate. Finally, the gas leakage rate through a concrete crack is presented.