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To improve the accuracy of erosion prediction, the effect of subsequent particles impacting the same area while the first single particle rebounds from the substrate must be considered. This issue has rarely been considered in studies pertaining to erosion damage. In the present study, the ABAQUS software is used to investigate the erosion crater morphology and stress distribution on a target material subjected to overlapping impacts of spherical particles. Subsequently, the validated model is applied to investigate the effect of the overlapping impacts of particles on the target. Accordingly, the correlation between erosion severity and the impact locations of the two incident particles is quantified. The results show that the horizontal distance between two solid particle impact locations can significantly affect the erosion magnitude and pattern. The interactions of the resulting craters diminish when the horizontal distance exceeds 0.6 times the particle diameter. When the horizontal distance is approximately 0.06 times the particle diameter, the energy loss originating from collisions reaches the maximum, which modifies the crater morphology. The present study is expected to provide in-depth insights into erosion mechanisms and erosion modeling.

Background: Capacitive micromachined ultrasonic transducers (CMUTs) is a promising component of mechanical-electrical-acoustical conversion, which shows valuable applications in non-distructive testing and obstacle detection fields. In order to study the influence of dimension parameters on the directivity of CMUTs, the three-dimensional multi-physics coupling model is proposed for CMUTs in this paper. Method: The model combines multiple physical fields through finite element method (FEM), which is more efficient and accurate. The influence of dimension parameters on the transducer is studied from two aspects: the pitch between adjacent cells and cell number, respectively. Results: When increasing the pitch, the directivity becomes better if the pitch is less than half of the wavelength, the grating lobe and side lobe are aroused. However, the bandwidth at -3dB is reduced by up to 71.1% at the same time. When increasing the cell number, the better the direcitvity, while the change of the cell number has little effect on the bandwidth of the array. However, 5.4% frequency shift was caused due to the effective mass change of the transducer. Conclusion: In this study, a 3D model based on FEM is proposed for the influence of dimension parameter on CMUTs. The simulation results indicate that the directivity can be enhanced by changing the dimension. At the same time, it also introduces other performance issues, such as bandwidth decrease and frequency shift through this approach. Therefore, the simulation proposed the guidance of CMUTs performance optimization work in the future.

Applying CO2 hydrate (referred to as hydrate) to CO2 storage and sequestration can alleviate global greenhouse effect, which is currently a hot spot of hydrate research. In order to explore the dissociation mechanism and rate, this paper carries out hydrate dissociation experiments under different working conditions of depressurization stage, temperature and initial hydrate volume fraction by using the reactor. Then, based on the experimental results, the influences of pressure, temperature, hydrate volume fraction, mass exchange and energy exchange on the dissociation rate are analyzed. Finally, a hydrate dissociation rate model considering the influences of intrinsic dissociation dynamics, mass transfer and other comprehensive mechanisms is established. And the following research results are obtained. First, two dissociation phenomena appear in the process of hydrate dissociation, including adsorption of gas bubble and shedding of flaky hydrate from the edge. Second, hydrate dissociation is a process of intrinsic dissociation dynamic driving, mass and heat transfer. According to the dissociation rate variation, it can be divided into two stages, i.e., stable dissociation stage and dissociation weakening stage. In the stable dissociation stage, the dissociation rate is maintained constant. And in the dissociation weakening stage, the dissociation rate decreases gradually with the increase of dissociation resistance (mass exchange). Third, both pressure and temperature drive the dissociation by influencing the difference between the actual hydrate surface fugacity and the phase equilibrium fugacity. The increase of depressurization range can lead to the increase of dissociation rate while the duration of stable dissociation is extending. The increase of temperature can also lead to the increase of the dissociation rate, but its influence is less than that of depressurization. In conclusion, this newly established dissociation rate model can well predict the value and variation trend of hydrate dissociation rate. And under the working condition of 2.0 MPa, the maximum relative error of the experimental results is 5.1%.

The coexistence of nanoparticles (NPs) and environmental pollutants has become a new type of pollution, and the co-adsorption behaviors of coexisting NPs and pollutants on the coconut shell porous biochar is important to explore the environmental fate of both pollutants and NPs in complex environments. In this study, the interaction between nano-titanium dioxide (n-TiO2) and tetracycline (TC) during the adsorption process on the coconut shell biochar (CBC) was explored by adsorption experiment, the co-adsorption mechanisms of TC and n-TiO2 onto CBC were discussed by morphology and characteristics of Scanning electron microscopy, Brunauer-Emmett-Teller specific surface area, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The results showed that the n-TiO2 in the TC + TiO2 binary system leads to the TC adsorption decrease by 54.60% averagely. The TC in the TC + TiO2 binary system increased the n-TiO2 adsorption by 31.97% averagely but weakened the adsorption affinity of n-TiO2. Characterization analysis confirmed that, the hydrogen bonding, π-π/n-π interaction and pore filling between TC and CBC were suppressed in the TC + TiO2 binary system. The TC in the binary system enhances the n-TiO2 adsorption on the outer surface and the inner surface of CBC by surface bridging and reducing the agglomeration of n-TiO2.

Erosion occurs in many industrial processes which results in economic losses and environmental issues. Having a more confident prediction method has always been the goal of the erosion community. Numerous studies have investigated erosion prediction utilizing Computational Fluid Dynamics (CFD) and many have obtained seemingly good agreement with experimental data. However, the uncertainties resulting from the grid size on erosion representation has not been investigated thoroughly. In this paper, one-way coupled discrete phase and Eulerian flow models are utilized to examine the effect of cell size on erosion calculated by CFD. It is found that both erosion pattern and magnitude can be easily affected by the grid size. Thus, an appropriate cell size range used to represent local erosion magnitude and the full erosion profile is proposed. The study provides guidelines for engineers to predict erosion in gas pipelines and quantify the uncertainties in a more deterministic fashion.

CO2 capture and storage technology is an effective method to mitigate the greenhouse effect and hydrate slurry is a high-efficiency way of CO2 transportation. In this study, in order to further reduce the cost and improve the transportability, a new CO2 hydrate slurry transport mode which allows a small part of hydrate particles to dissociate during flow process is proposed. To investigate the CO2 hydrate slurry flow characteristics and particle micro behaviors, a multiphase flow model coupled with hydrate dissociation kinetic model and population balance model is established. Experimental results are used to verify this integrated model. Furthermore, the effects of hydrate dissociation on CO2 transportability are also analyzed. The results indicate that the dissociation rate of hydrate during flow process can be divided into rapid dissociation stage and weakened dissociation rate stage. The agglomeration of hydrate particle can reduce the total surface area, further resisting the dissociation rate. The hydrate particle size experiences a process of growing to dynamic balance. The hydrate dissociation can decrease the mean viscosity of CO2 hydrate slurry flow, which can reduce the pressure drop and energy loss compared with the flow without hydrate dissociation. The generated bubbles can accelerate the CO2 hydrate slurry flow, increasing the transportability and reducing the risk of hydrate blockage in pipe induced by agglomeration.

Energy shortages and environment pollution are among the most important problems all over the world. As a clean and renewable energy carrier, hydrogen is expected to be one of the most promising alternative solutions to the energy and environmental problems in the near future. However, the safety issues in hydrogen production, transport and storage have to be thoroughly addressed before commercialization of hydrogen energy to give authorities confidence and to eliminate the public fear of using hydrogen. Accurate knowledge of the dispersion characteristics of unintended hydrogen releases in the atmosphere is essential to developing good standards and codes for hydrogen safety. This paper presents a numerical study on the indoor hydrogen leakage risk assessment and numerical simulation. The physical and mathematical model of hydrogen leakage and diffusion process are established. Based on computational fluid dynamics, the numerical simulation of hydrogen leakage process is studied. The effects of leakage source height and direction on hydrogen leakage and diffusion in indoor space are analyzed. The results show that the hydrogen leakage in the laboratory space is initially diffused by jet. With the development of time, the leaked hydrogen with different height and direction of leakage source forms different forms of vortex in the space, which affects the speed and amount of hydrogen accumulation in the space. When the hydrogen leakage source is low, the leakage direction is downward and back to the vent, the safety risk is greater.

The widespread presence of microplastics (MPs) in the Yangtze River, the third longest river in the world, has drawn increasing attention. Although numerous studies have been conducted recently to investigate and analyze the MPs exposure to the surface water of the river, most merely focus on a certain part of the Yangtze River, and knowledge of MPs based on the basin-wide is still scattered. This article reveals the spatial distribution characteristics of MPs in the Yangtze River from the whole watershed scale. Among the five areas in the basin, the upstream and the midstream were demonstrated to contain more MPs (3598.6 particles/m

In order to further understand the effect of solid impurities on pipeline wall during erosion, the particle impact process without fluid was extracted for specific study. The effect of multi-impact particles on the wall of pipeline was studied experimentally and simulated. In this experiment, an improved ejection apparatus was implemented to carry out multi-impacts non-overlapping impingement by rhombic particles made of high speed steel(W18Cr4V) on the AA6061 aluminum alloy plate through changing particle angle, incident angle, orientation angle and impact velocity. As a result, each particle's penetration depth was investigated and particles' rebound trajectory can be described through this experiment as well as surface morphology of the target material after impingement. The ductile damage criterion, shear damage criterion and MSFLD damage criterion were jointly implemented in ABAQUS/CAE software to simulate the whole process of collision which proved to be effective by getting consistent result compared with experimental data. It is found that under the condition of continuous non-overlapping impact, the target material produces a small work hardening effect in the impact area by converting kinetic energy of moving particles into internal energy of plate so as to reduce the penetration depth of each impact particle.

Many petroleum products like oil and gas are transported from one place to another through pipelines, although they can undergo leakage due to pipeline leaks and cause risks to industries, the environment, and people. In this review work, we have presented a comprehensive overview of acoustic emission technology for gas pipeline leak detection. Essential gas leak detection system requirements, principles, terminologies, and risks due to failure of the natural gas pipeline system have been discussed while proposing a surface acoustic wave sensor with a combination of the Hilbert–Huang transforms (HHTs) as the best method for real-time leak detection system in the gas pipeline network. The variation of wave energy causes propagation of elastic waves that can be detected by sensors mounted on the pipeline. Natural gas pipeline networks require a continuous real-time monitoring system to ensure that the pipelines are delivering the products from one station to another at optimum conditions.

Energy waste, environmental pollution, loss of human life and property can be caused once underwater gas leakage occurs. It is of great significance to establish an emergency response mechanism for underwater gas leakage and diffusion. A 3D model based on coupled Eulerian-Lagrangian approach is carried out to investigate the underwater release characteristics and diffusion law of gas leakage. The model is validated by the experimental data from literature and the results are accord with the experimental values. Influencing factors such as marine environment, leaking rate, current speed, and water depth are analyzed by numerical simulation. The calculation results indicate that ocean condition mainly affects underwater gas migration behaviors and gas plume consumes the longest rise time under wave and current. Water depth, current speed and leaking rate significantly influence the underwater gas migration but have limited effect on gas diffusion in atmosphere. The investigation will give some advice for emergency response formulation.

During the development of oil and gas fields, it is common for elbow suffering from sand wear. In this study, the erosion performance of 316 L stainless steel at the elbow was analyzed using the slug flow erosion experiment loop. The experiment was conducted under slug flow with different superficial air and water velocities using a detachable elbow. After weighing the mass loss and analyzing the sample surface, the erosion rates in different parts of the elbow were quantified and the erosion regularity was analyzed. The results indicate that the increase in superficial air velocity has a greater impact on the erosion rate than that in the superficial water velocity. The maximum erosion damage occurs at the outer wall in the 67.5° position. With the increase in superficial air and water velocity, the number of scratches on the maximum erosion position reduces.

To improve the accuracy of the erosion prediction, it is necessary to consider the influences of adjacent particles in the calculations. Therefore, in the present work Johnson-Cook hardening criterion and Johnson-Cook damage criterion are used in ABAQUS software to study erosion crater morphology and stress distribution on target materials subjected to overlapping impacts of spherical particles. The results show that the impact location of the adjacent particles, which is defined as the horizontal distance between the solid particle impacting spot, can significantly affect the erosion magnitude and pattern. As the horizontal distance between two impacts increases from 0 to 0.6 times the particle diameter, the interaction of the craters gradually decreases. When the horizontal distance is beyond 0.6 times the particle diameter, the interaction between two craters is disappeared. Furthermore, the depth difference between two craters is increased under the impact of adjacent particles. As the impact velocity increases from 14 m/s to 22 m/s, the difference between the depth of two craters is increased from 3.23 μm to 14.7 μm. When the impact angle increases from 25° to 85°, the depth difference between the two craters is increased from 0.11 μm to 14.40 μm. The numerical simulation of erosion process can provide a scientific basis for more elaborate erosion modeling.

The existence of back pressure will cause shock wave in the Laval nozzle of the supersonic separator, which will lead to the condensed droplets to evaporate and reduce the separation efficiency of the separator. It is of great significance to determine the shock position and avoid the secondary evaporation of droplets for improving the separation efficiency. In this paper, one-dimensional isentropic flow function method was used to calculate the shock position in nozzle. A mathematical model of methane-water vapor was established. The results show that the pressure energy recovery leads to the shock wave. With the increase of energy recovery efficiency, the position of shock wave moves to the throat, which shortens the droplet growth space and reduces the liquefaction of Laval nozzle. When the pressure energy recovery efficiency is 56.25%, the liquid mass fraction is 1.63% at the outlet. The shock wave position error of theoretical calculation and numerical simulation increases with the enlargement of divergent angle when considering condensation. The average error between numerical simulation and theoretical calculation results was less than 5%, thus the one-dimensional isentropic flow function method can provide a theoretical basis for predicting the shock position.

Gas hydrates can form in gas-liquid flow in the submarine natural gas production process, enormously challenging the flow safety. In this paper, a mathematical model is developed to describe the turbulent gas-liquid-hydrate multiphase flow system in horizontal and upward inclined pipeline. The population balance model is coupled for predicting the birth and death of hydrate particles, mainly concerning the collision, agglomeration and breakage mechanisms. Then, the effects of gas flow velocity, slurry flow velocity, hydrate volume fraction and pipeline inclination on the flow pattern and particle size distribution are analyzed. Moreover, considering the flow pattern transferred from stratified flow to slug flow, particle behaviors at slug body are also discussed. The results indicate that hydrate particles incline to agglomerate and locate at the bottom layer of pipe. Increase of hydrate volume fraction and hydrate slurry flow velocity will induce the flow pattern transition and intensification of particle agglomeration. Hydrate particle size distribution is more symmetrical at upward inclined part and eventually achieving a balanced state of agglomeration and breakage. The results can provide suggestions for avoiding gas hydrate blockage induced by agglomeration of hydrate particle in practical gas production.

A new method was proposed for hydrogen sulfide removal from natural gas through the utilization of supersonic flow in a Laval nozzle. For this purpose, a mathematical model was established for the supersonic non-equilibrium condensation flow of the binary methane-hydrogen sulfide mixture. The condensation parameters were numerically calculated and described in detail, and a sensitivity analysis was carried out to investigate the influence of the inlet parameters on the supersonic condensation flow. The results show that when the inlet temperature and pressure were 290 K and 5 MPa respectively, and the mole fraction of hydrogen sulfide was 15%, the removal efficiency of hydrogen sulfide was 64.83%, which indicates that the use of supersonic separation technology for this application is indeed feasible. It was also found that with the decrease of inlet temperature or the increase of inlet pressure, the nucleation site moved forward (i.e. closer to the throat), and the maximum droplet radius and liquid mass fraction of hydrogen sulfide increased. When the mole fraction of hydrogen sulfide was less than 5%, however, the liquid mass fraction of hydrogen sulfide was almost zero. Therefore, it appears that using a reasonable hydrogen sulfide fraction, a lower inlet temperature, and a higher inlet pressure can promote the supersonic condensation of hydrogen sulfide in the Laval nozzle and improve the efficiency of the removal process. These results suggest that supersonic separation technology can provide an efficient and environment-friendly way to remove hydrogen sulfide from natural gas, thereby reducing emissions.

Great threats and damages to natural ecosystem and marine environment will be caused once oil and gas leakage occurs. It is crucial to develop a quick response strategy, including the accurate prediction of oil and gas migration path, oil droplet size distribution and other parameters. Volume of fluid (VOF) model and realizable k-e turbulence model are employed to investigate the underwater spreading characteristics and migration law of oil leakage. Influencing factors such as wave length, leakage direction, current speed, wind speed, oil density, and leaking rate are analyzed by numerical simulation. The calculation results indicates that wave length affects both the underwater spread and drift process, while current speed and wind speed mainly influence the drift process. Leakage direction, oil density and leaking rate have significant influence on underwater spread process but limited effect on drift process. A formula is proposed to predict the oil diffusion distance at certain time. The results of investigation can offer a valuable guidance for formulation of emergency response.