Leakage Hole Research Articles

Numerical analysis of the diffusion and explosion characteristics of hydrogen-air clouds in a plateau hydrogen refuelling station

The investigation of hydrogen diffusion and explosion characteristics after accidental hydrogen leaks in hydrogen refuelling stations can provide the theoretical reference of the safe application of hydrogen refuelling stations. The numerical study analyses the effects of plateau environment on the dispersion and explosion characteristics of combustible clouds, visualises the diffusion and explosion process of hydrogen-air combustible clouds and quantifies the hydrogen concentration and explosion pressure at monitoring points. Results show that combustible clouds may appear upstream of the leak hole due to the presence of obstacles. The low atmospheric pressure conditions in the plateau areas result in high hydrogen concentration near the blast wall and large combustible cloud size. The hydrogen concentration near the blast wall and combustible cloud volume are also shown a positive correlation with air temperature, which will be detrimental to fire protection in hydrogen refuelling stations. After the explosion of the hydrogen clouds, the mortality zone (explosion overpressure ≥0.69 bar) is observed near the blast wall and at high leak volumes, the hazardous zone (0.07 bar ≤ explosion overpressure ≤0.69 bar) may spread over the blast wall into the crowded area. However, the blast wall blocks the development of the high-temperature zone, which has a positive effect on preventing the spread of the explosion flame. An examination of the pressure monitoring point data reveals that there appears to be an opposite effect of atmospheric pressure on the positive and reverse overpressure. The maximum peak blast overpressure in calculated domain indicates that both higher air temperatures and atmospheric pressures promote the growth of explosion overpressure.

Acoustic injection method based on weak echo signals for leak detection and localization in gas pipelines

Underground gas pipelines are facing health and safety issues due to the material corrosion and equipment aging. Conventional acoustic methods may fail to detect and localize leaks in low and medium pressure gas pipelines because the sound of gas escaping from a leak source is usually too weak to be detected. In this paper, an active acoustic injection method is presented to stimulate specific frequency sound waves into the pipeline for leak detection based on weak echoes from the leak location. Further analysis is conducted on the relationships between the reflection coefficient and the size of the leak hole, the pipe diameter, the wall thickness of the pipe and the sound frequency. A signal reconstruction method is subsequently proposed to effectively detect and localize the echo signals. Finally, some experiments are carried out in a specially constructed gas pipe. Field test results indicate that a leak localization accuracy of 0.1 m can be achieved by the proposed method, which may be beneficial to practical leakage detection in gas pipelines.

Study on multicomponent leakage and diffusion characteristics of hydrogen-blended natural gas in utility tunnels

With the rapid development of utility tunnels and hydrogen energy, hydrogen-blended natural gas (HBNG) enters gas compartments just around the corner. However, all safety requirements for gas compartments in current standards are designed for natural gas, and the applicability to HBNG is unclear. In addition, most of the existing diffusion models assume that the CH4/H2/Air mixture is single-component homogeneous gas, which cannot accurately describe the diffusion behavior differences between CH4 and H2. In this paper, an improved diffusion coefficient model for CH4/H2/Air non-ideal multi-component mixtures is proposed, which considers the interaction between CH4 and H2 components. After that, a 200 m long and narrow three-dimensional utility tunnel model is established to study the HBNG concentration distribution, alarm response time, and explosion hazardous area under different ventilation conditions. The effects of hydrogen blending ratio (HBR), leakage diameter, pipeline operating pressure, leakage location, and ventilation frequency on leakage and diffusion characteristics of utility tunnels are analyzed. The results show that under natural ventilation, the HBNG diffuses symmetrically to both sides with the leak hole as the center and covers the whole compartment after 1500 s. Normal mechanical ventilation reduces the distribution range and HBNG concentration, and the leaked gas covers the compartment downstream within 250 s. With the increase of HBR, the CH4/H2 mixture concentration increase at each monitoring point downstream of the leakage location, which causes the advance of the alarm response time. When the leakage reaches a steady state, the CH4/H2 mixture concentration for HBR of 5%, 10%, 15%, and 20% is 2.15%, 4.14%, 7.76%, and 10.97% higher than that of natural gas. The leakage location affects the hazardous area range, but little affects the CH4/H2 mixture concentration at the final steady state. The larger leakage diameter and the higher pipeline operating pressure can accelerate the HBNG diffusion rate in utility tunnels. When the pipeline operating pressure increases to 1.6 MPa, the current minimum accident ventilation frequency of 12 times/h is insufficient to reduce the CH4/H2 mixture concentration below the lower explosion limit (LEL). Increasing the ventilation frequency can effectively reduce the leaked gas concentration in utility tunnels, so it is recommended to increase the minimum accident ventilation frequency from 12 times/h to 15 times/h. The research results can guide the design and safety management of HBNG pipelines in utility tunnels.

Investigation of the leakage and diffusion characteristics of hydrogen-addition natural gas from indoor pipelines

The hydrogen-addition natural gas pipeline is a promising technology for large-scale civilian use, revealing the indoor diffusion behaviors of flammable gas in a leakage accident is of great importance for formulating a safety warning. A three-dimensional unsteady model is established, the distribution characteristics of CH4 and H2 are studied and the dynamic flammable regions are investigated. Case studies are performed to evaluate the effects of hydrogen-addition ratios and floor levels on average concentrations and flammable volumes of CH4 and H2. The results show that the high-concentration region of H2 is always near the leakage hole. The increase rate of flammable gas mixture volume is larger than that of the volume of high-concentration CH4. Under a higher hydrogen-addition ratio, the high-concentration region of CH4 and the flammable region of gas mixture both float up while the high-concentration region of H2 keeps horizontal, the flammable volume of gas mixture increases faster but the final volume is smaller. When the room is ventilated, a bigger wind speed leads to a smaller flammable volume of gas mixture. The flammable volume can be constrained at a quite low value from the beginning as the wind speed surpasses 1.5 m/s. When the leakage of hydrogen-addition natural gas occurs, floor 1 takes the most serious ignition risk with the largest flammable volume of 9.87 m3, occupying 44% of the room space. By contrast, the upper floors have quite smaller flammable volumes of gas mixture (under 0.05 m3) and the flammable region is near the leakage hole. The high-concentration region of H2 is affected slightly by the floor height.

Model Test of Surrounding Rock Temperature Field under Different Drainage Structures and Insulation Conditions in High Cold Tunnel

Improper layout of drainage structures and inadequate insulation measures in high-altitude cold areas have resulted in varying degrees of frost damage in numerous tunnels during operation. To address this issue and propose a viable drainage structure layout scheme, this paper analyzes and studies the temperature field distribution characteristics of the lower surrounding rock and drainage structure around high-altitude cold tunnels, as well as the layout of the central drainage ditch and anti-cold water leakage hole. Based on physical model test results of cold area tunnels, the distribution characteristics of the temperature field around the tunnel drainage structure under different insulation conditions are obtained, and a control equation of temperature change along the depth direction is proposed. By comparing and analyzing the differences in temperature field and water flow characteristics of drainage structures under different insulation methods, the setting conditions of different drainage structures are determined. Furthermore, the function relationship between the freezing depth of the lower surrounding rock of the tunnel arch and the air temperature inside the tunnel is established, and the curve of the on-site tunnel freezing depth change is predicted. This study provides valuable insights into the design and construction of drainage structures and insulation measures for high-altitude cold tunnels, ultimately contributing to the prevention of frost damage and ensuring safe and efficient tunnel operation.

Leakage and diffusion characteristics of underground hydrogen pipeline

Soil corrosion and hydrogen embrittlement are the main factors of hydrogen pipeline failure. The gas escapes, diffuses and accumulates in the soil and enters the atmosphere when leak occurs. The mechanism of gas diffusion in buried pipelines is very complicated. Mastering the evolution law of hydrogen leakage diffusion is conducive to quickly locating the leakage point and reducing the loss. The leakage model of the underground hydrogen pipeline is established in this paper. The effect of leakage hole, soil type, pipeline pressure, pipeline diameter on hydrogen leakage diffusion were investigated. The results show that when the hydrogen pipeline leaks, the hydrogen concentration increases with the increase of leakage time, showing a symmetrical distribution trend. With the pipeline pressure increase, hydrogen leakage speed is accelerated, and longitudinal diffusion gradually becomes the dominant direction. As the leakage diameter increases, hydrogen leakage per unit of time increases sharply. Hydrogen diffuses more easily in sandy soil, and its diffusion speed, concentration, and range are higher than that in clay soil. The research content provides a reference and basis for the detection and evaluation of buried hydrogen pipeline leakage.

Математическое моделирование натекания водорода в гермзоне реакторного здания АЭС с ВВЭР-1200

Introduction. The patterns of hydrogen-air mixtures formation during the flow of hydrogen into the upper part of a large volume room in the initial moments of time are insufficiently studied. Therefore, the determination of regularities of formation of local explosive and fire-hazardous hydrogen-air mixtures when hydrogen flows into the lower part of the dome space of the reactor building is important. Goals and objectives. The purpose of the article is a theoretical study of occurrence of local fire and explosive zones of the hydrogen-air mixture generated during hydrogen leakage in the containment area of the reactor building in order to substantiate parameters of concentration sensors of the hydrogen concentration control system. To achieve it, a zone mathematical model of hydrogen concentration calculation in a pressurized room has been developed. Numerical experiments on regularities of hydrogen-air mixtures formation have been carried out. Theoretical basis. The generalized three-dimensional non-stationary differential equation of the laws of conservation of mass, momentum and energy is used to calculate local hydrogen concentration fields. The developed zone model makes it possible to determine hydrogen concentrations in the convective column and in the ceiling layer. Results and discussion. The characteristic fields of hydrogen mass concentrations in the volume of the dome space are obtained. It has been shown that at the initial stage of hydrogen leakage, a zone of the ceiling layer is formed under the ceiling of the dome space, which confirms the validity of the usage of the zone model. The hydrogen concentrations obtained by the field and zone models are compared. The distributions of hydrogen mass concentration along the convective column height at different Reynolds numbers in the hydrogen leakage hole have been obtained. It has been shown that hydrogen concentration sensors can detect a hydrogen leakage mode in the dome space only in a narrow area of Reynolds Re = 900–5,000. There is a leakage mode (Re = 3,358), in which the maximum hydrogen volume concentration is generated at the location of the concentration sensors at the maximum size of the fire and explosive hydrogen-air mixture zones in the room. Conclusions. The hydrogen concentration sensors used in the dome space of the NPP reactor building with water-­water reactors may not detect hydrogen at the top point of the dome at a sensitivity threshold of 2 % vol. In this case, in terms of the height of the convective column, hydrogen-air mixtures are formed within the fire and explosive concentration limits.

Multi-Factor Coupling Analysis of Porous Leakage in Underwater Gas Pipelines

Natural gas pipeline leaks under the sea will have a significant negative effect on the marine ecosystem, result in significant financial losses, and possibly even harm marine floating objects. The VOF (Volume of Fluid) multi-phase flow model is used to numerically simulate and study the diffusion process of porous leakage in submarine gas pipelines. Experiments confirmed the model’s correctness and dependability. Based on this, the coupling effect and the porous effect of the leakage velocity, the size of the leaked pore, and water velocity of the natural gas pipelines on the diffusion of porous leakage in the submarine gas pipelines are analyzed with the test scheme designed by the orthogonal test method. The similarity principle is used to connect the leakage model with the actual application. The results show that three factors, namely, the leakage velocity, the size of leaked pore, and the water velocity, influence the shape of the air mass, the time when the gas reaches the sea surface, and the diffusion range. The size of the leakage hole and the leakage velocity have a substantial impact on the form of the air mass and the amount of time it takes for the gas to reach the sea surface, while the water velocity has no effect. Additionally, while there is essentially little impact from the leakage velocity, the size of the leaky pore and the water velocity have a significant impact on the diffusion range. Furthermore, the porous effect between leaky pores has a significant impact on the gas diffusion range. This study can serve as a guide for risk assessment and emergency decision-making regarding a submarine gas pipeline leak.

Numerical simulation of hydrogen leakage diffusion in seaport hydrogen refueling station

Ningbo's seaport hydrogen refueling station was used as the research object. The effects of different leakage angles, wind direction, roof shape, leakage hole diameters, temperature, and humidity on the diffusion of hydrogen leakage were studied by numerical simulation. The influence of leakage angle on hydrogen leakage is mainly reflected in the presence or absence of obstacles. The volume of the flammable hydrogen cloud was reduced by 31.16%, and the volume of the hazardous hydrogen cloud was reduced by 63.22% when there was no obstacle. The wind direction can significantly impact hydrogen leakage, with downwind and sidewind accelerating hydrogen discharge and reducing the risk. At the same time, headwind significantly increases the volume of the flammable hydrogen cloud. Compared with no wind, the volume of the flammable hydrogen cloud increased by 71.73% when headwind, but the volume of the hazardous hydrogen cloud decreased by 24.00%. If hydrogen shows signs of accumulation under the roof, the sloping roof can effectively reduce the hydrogen concentration under the roof and accelerate the hydrogen discharge. When the leakage angle θ = 90°, the sloping roof reduced the volume of the flammable hydrogen cloud by 11.74%. The leakage process was similar for different leak hole diameters in the no wind condition. The inverse of the molar fraction of hydrogen on the jet centerline was linearly related to the dimensionless axial distance of the jet in different cases. Using a least squares fit, the decay rate was obtained as 0.0039. In contrast, temperature and humidity have almost no effect on hydrogen diffusion. Hydrogen tends to accumulate on the lower surface of the roof, near the roof pillars and the hydrogen dispenser. In this paper, a set of hydrogen detector layout schemes was developed, and the alarm success rate was verified to be 83.33%.

Explosion risk analysis of R290 leakage into a limited external space

R290 is considered as a promising alternative refrigerant to be used in household air conditioners. To promote the safety application of R290 in air conditioners, a numerical model of refrigerant leakage and diffusion in a limited space was developed, and the reliability of the model was verified by the experimental results on the concentration field of refrigerant leakage from a split air conditioner indoor unit. On this basis, the field strength characteristics of R290 leaking from holes with different diameters and shapes to the external space were investigated, and the explosion risk caused by R290 leakage was further analyzed. The results showed that when R290 leaked from circular leakage holes with different diameters or leakage holes with different shapes to the external space, respectively, Mach disks were formed in the flow area, and the location and size of the Mach disks had certain differences. For circular leakage holes, with the increase of the leakage diameter, the diameter of the Mach disk inside the flow area and the distance from the Mach disk to the leakage hole increased, and the range of the flammable area formed by the leaked R290 in the external space did not change significantly in the horizontal direction, but increased significantly in the vertical direction, which were 0.42 m, 0.84 m, 1.26 m, and 1.7 m, respectively. For leakage holes with the same area but different shapes, the diameter of the Mach disk formed by the gas leaking from the circular hole was larger, and the gas was distributed symmetrically in the horizontal direction with the jet axis as the center in the external space. The gas leaking from the triangular hole was approximately distributed in a triangular shape, and then it diffused along the three centerlines of the triangle. The gas leaking from the square hole diffused along the diagonal of the square in the horizontal direction, and finally the flow area gradually changed from a square to a circle. The gas leaking from the rectangular slit was elliptically distributed in the external space, and the gas mainly diffused along the long axis direction of the ellipse, and the diffusion of the short axis direction was not significant. The range of the flammable area formed by the gas leaking from holes of different shapes did not change significantly in the external space.

Experimental Study of External Pipe Wall Erosion due to Water Pipe Leakage

Burst pipes can cause severe pressure drops and water pollution in water distribution networks. Small leaks can develop into pipe bursts over time due to interactions between pipes, water, and soil. This paper presents preliminary experimental results on the erosion of the outer wall of a pipe by solid particles when a leak occurs in a pressurized pipe and causes soil fluidization. A series of experiments were carried out with 50-mm-diameter and 3-mm-wall-thickness polyethylene (PE) pipes with various leak holes buried in silica sand bedding. The experiments investigated the effects of the leak size, shape, and direction on the erosion process. The findings indicated that the size of the leaks had the greatest impact on erosion rate, and erosion rate was nearly completely unaffected by the geometry of the leak hole or leak orientation.

Multi-leakage source localization of safety valve based on improved KDE algorithm

The safety valve is the core component of the safety pressure relief protection device of the pressure-bearing special equipment. When the safety valve leaks, the medium of the pressure vessel will be lost and wasted, which may lead to safety accidents. Aiming at the problem that it is difficult to accurately locate multiple tiny leak holes in safety valves, multi-leakage source localization of safety valve combining the acoustic emission (AE) test with improved approximate kernel density estimation (KDE) algorithm is proposed. The algorithm first introduces the improved wavelet threshold function denoising method to extract the time-frequency support domain which is less affected by environmental noise and the energy of the leaked sound source is dominant, which makes the premise of the application of the KDE algorithm established. In the aspect of improving the wavelet threshold function, an improved adaptive wavelet threshold noise reduction method is proposed by using the decay characteristics of the exponential function. On this basis, the high-frequency aliasing is suppressed by frequency division fusion processing, the approximate kernel density function is calculated, and the three-dimensional spectral base of the approximate kernel density function is reduced. Through numerical calculation, the location coordinates of the leakage source of the safety valve are obtained according to the peak value of the improved KDE spectrum. The results show that the relative errors of the leakage location results of safety valves with working pressures of 0.72 MPa, 0.75 MPa and 0.77 MPa are all within 10%. The method of combining the acoustic emission test with the improved KDE algorithm can accurately locate the leakage source of the safety valve, and with the increase of the working pressure of the safety valve, the positioning accuracy is also improved accordingly.

Analysis of the Influencing Factors of the Leak Detection Method Based on the Disturbance-Reflected Signal

Leak detection technology, based on the disturbance-reflected signal, can realize pipeline state inspection without relying on the transient characteristics of leakage. However, the lack of research on the factors affecting the detection effect of this method greatly restricts its popularization and application. Therefore, this paper realizes the valve opening and closing through dynamic mesh technology and further establishes a 2D pipeline disturbance and reflection signal detection model. The correctness of the computational fluid dynamics (CFD) model detection mechanism was verified by theoretical analysis and indoor pipe flow experiments. In this process, it was found that reflections from boundaries, such as the pipe end, could also be identified and did not interfere with leak-related signals. In addition, the positioning errors of the leakage hole and the pipe end were 4.447% and 0.121%, respectively, and accurate positioning with zero error was able to be achieved in the calculation results of the CFD model. Finally, the influence factors of the detection effect of this method were analyzed by inputting the determined disturbance signal. Both the disturbance signal characteristics and the leakage hole characteristics affected the reflected signal, and the former played a more prominent role. Surprisingly, the results showed that pipeline flow and pressure had very limited influence on this method.

Cause Analysis of Economizer Tube Leakage in a Biomass Power Plant

Aiming at the leakage of economizer tube in a biomass power plant, the leakage mechanism of economizer tube was studied by means of macro analysis, chemical composition analysis, metallographic structure, micro Vickers hardness test and scanning electron microscope. The results show that there is no misuse of materials or unqualified chemical composition in the leaked economizer tube; The metallographic microstructure is ferrite + pearlite, and the spheroidization level is between 2.0 and 2.5, indicating that there is no obvious spheroidization in the pipe section submitted for inspection; At the same time, the micro Vickers hardness value did not decrease significantly; The outer wall of the pipe is yellowish brown and there is delamination and peeling of attachments. A leakage hole can be seen in the middle of the pipe section, and there is obvious thinning at the edge of the hole, indicating that there is corrosion thinning. The chemical components of the corrosion products are mainly Fe and O, and contain a certain amount of Cl, s, P, Si, K, Ca and other alkali metal elements. Therefore, it can be inferred that the main cause of economizer pipe leakage is corrosion thinning.

Modeling of Hydrogen Blending on the Leakage and Diffusion of Urban Buried Hydrogen-Enriched Natural Gas Pipeline

With the introduction of various carbon reduction policies around the world, hydrogen energy, as a kind of clean energy with zero carbon emission, has attracted much attention. The safe and economical transportation of hydrogen is of great significance to the development of hydrogen energy industries. Utilizing natural gas pipelines to transport hydrogen is considered to be an efficient and economical way. However, hydrogen has a higher risk of leakage due to its strong diffusion capacity and lower explosive limit than conventional natural gas. Therefore, it is of great significance to study the leakage and diffusion law of hydrogen-enriched natural gas (HENG) pipelines for the safe transportation of hydrogen energy. In this study, the leakage and diffusion characteristics of urban buried HENG pipelines are investigated numerically, and the dangerous degree of leakage is analyzed based on the time and area when the gas concentration reaches the lower explosive limit. The influences of hydrogen blending ratio (HBR), operating pressure, leakage hole size and direction, as well as soil type on the leakage and diffusion law of HENG are analyzed. Results show that the hydrogen mixing is not the key factor in increasing the degree of risk after gas leakage for urban buried HENG pipelines. When the HBR is 5%, 10%, 15% and 20%, the corresponding first dangerous time is 1053, 1041, 1019 and 998 s, respectively. This work is expected to provide a valuable reference for the safe operation and risk prevention of HENG pipelines in the future.

Numerical Study of Casing Microleakage Flow Field Sensitivity and Acoustic Field Characteristics

The casing leakage phenomenon seriously affects the safety and economic problems of oil and gas production and transportation. In this paper, the numerical simulation study of the casing's micro-leakage flow field and acoustic field is carried out by taking the oil and gas well casing as the research object. The CFD numerical model of the casing micro-leakage is established, and the influence of the size of the leakage hole, the shape of the leakage hole, and the pressure difference between the inside and outside the casing on the microleakage flow field is analyzed. An acoustic-vibroacoustic coupling calculation model based on Fluent and LMS Virtual LAB is established, and the sound pressure value and distribution at different frequencies are calculated. The results show that the flow rate of the leakage hole increases with the pressure difference between the inside and the outside leakage hole and the area of the leakage hole. Moreover, the flow rate of the circular leakage hole is higher for the same leakage hole area. The simulation model based on the equivalent sound source can be used to calculate and analyze the sound field in the tubing. By sound field computation based on the near-field equivalent sound source, when the frequency is 32,000 Hz, the amplitude of sound pressure is maximum. In addition, the sound pressure is greatly reduced once the sound wave passes through the tubing pipeline. Lastly, the sound pressure is higher at the position facing the leakage hole in the tubing, making detecting the leakage sound field signal easier. The results can provide a reference for further research on oil casing microleakage detection technology.

MATHEMATICAL MODEL OF PNEUMATIC CHANNEL OF GAS PRESSURE MEASURING TRANSDUCER

The paper is devoted to the study of the impact of operational factors, particularly gas leakage through the damages of pneumatic channels of measuring transducers of gas pressure and pressure drop, on the measuring result of these parameters and, therefore, on the measured value of gas flow rate and volume using pressure differential flowmeters. During the operation of gas metering units, connecting tubes, valve blocks, and averaging chambers of the standard primary device must be hermetic. However, they may become non-tight because of operational factors, and gas leakage may occur. Such leaks distort the measured pressure drop or pressure value, which can lead to a distortion of the measurement result of the gas flow rate by the metering unit.
 The authors developed a mathematical model of a pneumatic channel of gas pressure measuring transducer with existing damage. For this purpose, a mathematical model of the connecting tube, which connects the pressure averaging chamber with the pressure transducer chamber, has been developed for the stationary gas mode. A mathematical model of gas leakage through damage like "through-hole" was also developed. Based on the mathematical model of the connecting tube and the model of the process of gas leakage through the hole, a mathematical model of the pneumatic channel with a gas leakage hole was obtained.
 Modeling and investigating the impact of gas pressure, geometric characteristics of damage, and connecting line on the measuring result of pressure or pressure drop was performed. Particularly, the value of the negative systematic error of the gas pressure measurement, which occurs as a result of gas leakage through the hole in the connecting tube, is calculated for a set of fixed values of the geometric characteristics of the pneumatic channel.
 The paper shows that an increase in the pressure in the measuring tube leads to an increase in the modulus of pressure absolute error caused by the gas leakage through the hole in the connecting tube. The gas flow rate through the hole in the connecting tube and, accordingly, the pressure measurement error depends on the diameter of the through-hole and the location of the leakage. An increase in the hole diameter leads to an increase in the modulus of the absolute error of the pressure measurement.
 As the length of the connecting tube from the connection point with the measuring pipeline to the point of gas outflow increases, the pressure measurement error increases by the modulus.

A mathematical model of critical releasable charge for R290 indoor leakage of split-type household air conditioners

The leakage of hydrochlorofluorocarbons and hydrofluorocarbons used as refrigerants will not only cause ozone depletion and global warming, but also pollute indoor air. Propane (R290) not only does not damage the ozone layer and has a negligible greenhouse effect, but also its charge is about 20–50% of that of hydrochlorofluorocarbons and hydrofluorocarbons, and the releasable charge is lower. In the previous study, a refrigerant pump-down method was proposed to control the R290 releasable charge of split-type household air conditioners (STHACs) under off-mode below the critical releasable charge (CRC) to prevent fires. CRC varies with leakage conditions, such as leak hole sizes, the distance between the installation height of the indoor unit (IDU) and the ignition source (dispersion distance), and the construction of IDU, etc. In this study, a mathematical model is developed to predict the CRCs for STHACs with different capacities and constructions under various leak conditions. The model is verified to have a deviation within 10% for the vast majority of data-points by ignition experiment and CFD model. For safety, the CRC prediction formula is optimized to under-predict CRCs properly, therefore, CRCs for various STHACs and leak conditions are determined to prevent the formation of flammable mixtures even directly under IDU, and the indoor air quality will also be improved. For the used 1 HP STHAC, the predicted CRC is 6.6 g under a 0.5 mm2 leak hole and a 0.7 m dispersion distance.

Flame characteristics and heat flux profile of a tank surface caused by horizontal gas leak jet fire impingement

Jet fire accidents caused by leaks in gas pipelines or gas tanks often occur, which may trigger a domino effect. The present work experimentally investigated the characteristics and heat flux profile of flames on a tank surface, with different leak hole-tank spacing and fuel initial velocity. The results show that, for any given leak hole diameter, the height and width of the impingement flame increase with an increasing heat release rate, whereas they decrease with an increase in the leak hole-tank spacing. The impingement flame height correlated well with the characteristic length Lm, which was used in free jet fires. Based on the balance of the momentum flux to the buoyancy flux of the horizontal jet fire, a new characteristic length scale and a dimensionless heat release rate was proposed. Meanwhile, some of the numerical results were also analyzed and the non-dimensional functional correlation for the flame width of the impinging area was proposed with the fire heat release rate and flame Froude number Frf. Finally, considering the effect of the unburned portion of the fuel with jet fire impinging the tank, a new correlation was proposed to describe the heat flux and temperature profile of the tank surface.

Modeling and assessment of accidental subsea gas leakage using a coupled computational fluid dynamics and machine learning approaches

All over the world, the oil and gas industries are the most important source of energy. The likelihood of subsea gas and oil leakage is increasing, which can cause threats and harmful impacts on the marine environment and potentially catastrophic events such as fires, explosives, and the loss of structural integrity of subsea infrastructure. Also, Physical models have usually been used to predict sea currents, but they are unstable to disturbances and hence incorrect over long periods of time. Machine learning approaches are more resistant than the physical models that have usually been used to predict sea currents. Also, Physical models have usually been used to predict sea currents. Nonetheless, they are not stable to disturbances and thus are not correct for long periods of time. Machine learning approaches are more resistant than the physical models that have usually been used to predict sea currents. Machine learning approaches are more resistant to change and perturbation. Therefore, the goal of this research is to assess the potential of hazards of the gas plume from subsea pipeline rupture till reaching the sea surface by changing the influence parameters on gas plume to assist petroleum companies in developing risk assessment strategies by assessing and simulating subsea gas release in order to contain the leakage by developing coupling models one for machine learning code which can predict the upcoming water current speed by using Multiple Linear Regression algorithm and hooked it by UDF to a second model which implements Computational Fluid Dynamics (CFD) model to study subsea gas release under current effects. Engebretsen’s Rotvoll experiment data is being used to validate the numerical computational fluid dynamics model. The rising time and fountain height and horizontal migration for gas release are the essential factors to be considered while evaluating the gas dispersion through our study by changing the influencing parameters such as leakage hole sizes, water current speeds, gas velocity, and water depths in the presence of water current in all cases. Also, applied our simulation to real case parameters for one of the Egyptian Petroleum Companies. These findings might aid in evaluating the hazards and response planning in the event of subsea gas leakage.