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Currently, there is limited research on the in situ forming process of thermoplastic prepreg tape winding, and the unclear impact of process parameters on mechanical properties during manufacturing is becoming increasingly prominent. The study aimed to investigate the influence of process parameters on the mechanical properties of thermoplastic composite materials (CFRP) using laser-assisted CF/PPS winding forming technology. The melting point and decomposition temperature of CF/PPS materials were determined using DSC and TGA instruments, and based on the operating parameters of the laser-assisted winding equipment, the process parameter range for this fabrication technology was designed. A numerical model for the temperature of laser-heated CF/PPS prepreg was established, and based on the filament winding process setup, the heating temperature and tensile strength were simulated and tested. The effects of process parameters on the heating temperature of the prepreg and the tensile strength of NOL rings were then analyzed. The non-dominated sorting genetic algorithm (NSGA-II) was employed to globally optimize the process parameters, aiming to maximize winding rate and tensile strength. The results indicated that core mold temperature, winding rate, laser power, and their interactions significantly affected mechanical properties. The optimal settings were 90 °C, 418.6 mm/s, and 525 W, achieving a maximum tensile strength of 2571.51 MPa. This study provides valuable insights into enhancing the forming efficiency of CF/PPS-reinforced high-performance engineering thermoplastic composites.

Abstract Durable superhydrophobic anti‐erosion/anticorrosion coatings are highly demanded across various applications. However, achieving coatings with exceptional superhydrophobicity, mechanical strength, and corrosion resistance remains a grand challenge. Herein, a robust microstructure coating, inspired by the cylindrical structures situated on the surface of conch shell, for mitigating erosion and corrosion damages in gas transportation pipelines is reported. Specifically, citric acid monohydrate as a pore‐forming agent is leveraged to create a porous structure between layers, effectively buffering the impact on the surface. As a result, the coating demonstrates remarkable wear resistance and water repellency. Importantly, even after abrasion by sandpaper and an erosion loop test, the resulting superhydrophobic surfaces retain the water repellency. The design strategy offers a promising route to manufacturing multifunctional materials with desired features and structural complexities, thereby enabling effective self‐cleaning and antifouling abilities in harsh operating environments for an array of applications, including self‐cleaning windows, antifouling coatings for medical devices, and anti‐erosion/anticorrosion protection, among other areas.

The use of a supersonic separator presents a novel approach for separating ammonia (NH3) from hydrogen (H2). Even trace amounts of water (H2O) can significantly influence the condensation characteristics of NH3. This study presents mathematical models for homogeneous NH3 and H2O condensation and heterogeneous NH3–H2O condensation. Through computational analysis, we revealed that the droplet radius and liquid mass fraction of a single condensable gas condensation increased accordingly with increasing inlet condensable gas content. Interactions between the condensation processes of NH3 and H2O were also captured in the simulation. Notably, at 100 ppm H2O content, H2O spontaneously condensed before NH3, serving as a condensation nucleus for NH3, and the heterogeneous condensation of NH3 decreased the rate of its spontaneous condensation. At an inlet H2O content of 50 ppm, the onset of spontaneous NH3 condensation coincided with that of H2O, with H2O having a negligible effect on NH3 condensation. The impact of H2O on NH3 condensation transitioned from minimal to inhibitory and then to facilitative as the content of H2O increased from 25 ppm to 250 ppm. At the nozzle outlet, the liquid mass fraction of NH3 initially decreased from 0.0414 to 0.0352 and then increased to 0.0446.

Recent investigations into the erosion of elbow junctions predominantly focus on identifying and predicting peak erosion points. Notably, these studies rely heavily on computational fluid dynamics methods, a valid approach but limited by its lack of empirical physical data. Additionally, the majority of these studies concentrate on the extrados, or outer curve of the elbow, neglecting the intrados or the inner curve. To provide a more comprehensive understanding of particle movements and the micro-mechanics of erosion on the elbow intrados, this study utilizes advanced observational technologies. High-speed camera technology, coupled with scanning electron microscopy, is employed to capture and record particle motion and micro-erosion patterns. The erosion rate is then estimated via the weight-loss method. The findings suggest that in low-speed liquid–solid flows (2.5 m/s), particles released from the intrados side of the elbow inlet exhibit a significant trajectory deviation from the centreline at an elbow angle of 60° from the inlet. Particles released from the extrados deviate towards the intrados side at an elbow angle of 30°. Secondary flow contributes to particle acceleration, unexpected trajectory deviation within the elbow, and an upward inclination in erosion on the intrados. The presence of partially overlapping scratches and cracks suggests that continuous ploughing and material fracturing are significant contributors to the micro-mechanics of erosion. When comparing the intrados and extrados, the extrados exhibits longer and shallower scratches, indicating a smaller impact angle. This research provides a more comprehensive understanding of particle trajectories and erosion patterns within elbow junctions during liquid–solid flows, offering new insights into the mechanisms underpinning these processes.

Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering.

During the coal mining process in soft rock mines with abundant water, the rock mass undergoes cyclic loading and unloading at low frequencies due to factors such as excavation. To investigate the mechanical characteristics and energy evolution laws of different water-containing rock masses under cyclic disturbance loading, a creep dynamic disturbance impact loading system was employed to conduct cyclic disturbance experiments on various water-containing soft rocks (0.00%, 1.74%, 3.48%, 5.21%, 6.95%, and 8.69%). A comparative analysis was conducted on the patterns of input energy density, elastic energy density, dissipated energy density, and damage variables of different water-containing soft rocks during the disturbance process. The results indicate that under the influence of disturbance loading, the peak strength of specimens, except for fully saturated samples, is generally increased to varying degrees. Weakness effects on the elastic modulus were observed in samples with 6.95% water content and saturated samples, while strengthening effects were observed in others. The input energy density of samples is mostly stored in the form of elastic strain energy within the samples, and different water-containing samples adapt to external loads within the first 100 cycles, with almost identical trends in energy indicators. Damage variables during the disturbance process were calculated using the maximum strain method, revealing the evolution of damage in the samples. From an energy evolution perspective, these experimental results elucidate the fatigue damage characteristics of water-containing rock masses under the influence of disturbance loading.

The extensive usage of fossil fuels has caused significant environmental pollution, climate change and energy crises. The significant advantages of hydrogen, such as cleanliness, high efficiency, and a wide range of sources, make it quite promising. Hydrogen is prone to material damage, which may lead to leakage. High-pressure leaking hydrogen is highly susceptible to spontaneous combustion due to its combustion characteristics, which may cause jet fire or explosion accidents, resulting in serious casualties and property damage. This paper presents a detailed review of the research progress on hydrogen leak diffusion characteristics, leak spontaneous combustion mechanisms and material hydrogen damage mechanisms from the perspectives of theoretical analysis, experiments and numerical simulations. This review points out that although a large number of research results have been obtained on the safety characteristics of hydrogen, there are still some deficiencies and limitations. Further research topics are clarified, such as further optimizing the kinetic mechanism of the high-pressure hydrogen leakage reaction and turbulence model, exploring the expansion and dilution law of hydrogen clouds after liquid hydrogen flooding, further studying the spontaneous combustion mechanism of leaked hydrogen and the interaction between mechanisms, and investigating the synergistic damage effect of hydrogen and other components on materials. The leakage spontaneous combustion process in open space, the development process of the bidirectional effect of hydrogen jet fuel and crack growth under the impact of high-pressure hydrogen jet fuel on the material may need to be explored next.

The back pressure at the outlet of supersonic cyclone separator usually causes aerodynamic shock wave in Laval nozzle, and the interaction of supersonic flow, shock wave and phase transition is very complicated. In order to explore the supersonic flow properties of wet gas under the action of shock wave, study was performed on the methane-water vapor mixtures. Then, a mathematical model for the supersonic condensation and flow of wet natural gas was established. Meanwhile, the effect of the outlet back pressure and inlet pressure on the supersonic condensation property of wet natural gas was analyzed to evaluate the performance of the supersonic cyclone separator under the action of shock waves. The simulation results show that the shock waves can cause the rapid increase in pressure and temperature of water vapor in a short time, leading to the condensed droplets re-evaporate and the liquid mass fraction at outlet reduces sharply. Besides, as the inlet pressure increases, the location of nucleation approaches the throat of Laval nozzle gradually, and the limit nucleation rate and the droplet number decrease accordingly. However, the liquid mass fraction increases due to the increasing of growth rate and sizes of droplets. Moreover, the nozzle loses its function of liquefaction when the back pressure is higher than 25 kPa (i.e., the pressure ratio is higher than 0.58), and then the nozzle cannot operate normally. Therefore, it is necessary to control the reasonable pressure ratio to ensure the dehydration efficiency of the supersonic separator with back pressure.

Falling film evaporation is the core heat transfer mode of spiral-wound heat exchangers used in the liquefaction process of natural gas. In order to study the impact of different Reynolds numbers, outer diameters and spacings of pipeline on the parameters of the falling film flow of alkane media, such as the flow pattern and liquid film thickness, numerical simulation study of falling film flow was performed with the coupling model based on the VOF and Level Set two-phase flow models. Meanwhile, the numerical simulation model was verified by setting a visual experimental device. In addition, the calculating equation of liquid film thickness applicable to the alkane media was obtained by fitting based on the numerical simulation results. According to the results, the Reynolds number and the outer diameter of pipeline have great influence on the distribution of liquid film thickness. In the case that the outer diameter of pipeline is 4 mm, the liquid film thickness of falling film flow is uniform with poor stability at great Reynolds number (340–1 700). In general, the research results could provide theoretical guidance to the design and the safe and efficient operation of spiral-wound heat exchangers during the liquefaction of natural gas.

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%.

ABSTRACT: Elbow is one of the most accident-prone locations in multiphase flow lines, and understanding the flow field is the key to manage the risk. In the meantime, the flow characteristics of slug flow are most complicated in the flow field. To clarify the flow characteristics of slug flow at the elbow, the influence and mechanism of the elbow on the flow characteristics of slug flow under different superficial gas-liquid velocities were studied with experiments and numerical simulations. A set of transparent loops with gas-liquid two phase flow was built. High-speed camera, pressure sensor, Doppler velocimeter and wire mesh sensor were used to collect flow pattern, pressure, slug velocity and gas-liquid distribution characteristics. In the meantime, the multi-fluid volume of fluid (VOF) model was used in the CFD simulations, and the simulation results were compared against the experimental results for verification. The results showed that the void fraction is highest at the inlet and lowest at the middle position, and the pressure and flow velocity at the extrados were higher than those at the intrados of the elbow. With the increase of the superficial liquid velocity and gas velocity, the number of bubbles accumulated inside the horizontal elbow increased, the slug flow liquid film velocity of the horizontal elbow increased, and the secondary flow phenomenon weakened.

Erosion in multiphase flow is very common to the industrial piping systems and it will increase the safety risk of the piping systems. Once accidents occur, it will bring about serious economic loss and environment pollution.By investigating the research on the erosion of multiphase pipelines, the progress of research at home and abroad was presented in terms of the theoretical model, the erosion test, the numerical simulation and the microscopic mechanism. Meanwhile, the existing problems in current research on erosion of multiphase pipelines were pointed out and discussed, and the development direction in future was also clarified. In general, the research results could provide reference for the deep understanding and mastering of the erosion mechanism of multiphase pipelines, as well as the safe and efficient development and transportation of oil and gas resources.

The crystallization behavior of wax molecules is the root cause of wax deposition. In this study, molecular dynamics simulations were used to investigate the aggregational crystallization behavior of wax molecules in a crude oil system. The results show that wax molecules produce ordered wax crystal structures from the disordered liquid phase crude oil system under van der Waals forces at low temperatures. The crystallization of wax molecules consists of three main processes: carbon chain extension, nucleation of wax molecules and wax crystal growth. The lower the temperature of the crude oil system and the lower the cooling rate, the higher the degree of aggregation of wax molecules, the smaller the number of wax crystals and the larger the crystal size. In addition, asphaltene molecules are found to aggregate by face-to-face stacking and T-shaped stacking at low temperatures. Based on the spatial steric hindrance effect, the asphaltene aggregates prevent further aggregation between wax crystal clusters. Asphaltenes lead to an increase in the liquid content of the wax deposit layer, causing the yield stress of the deposit to decrease and the structural strength to weaken.

In order to study the influence of collision between solid particles in gas-solid two-phase flow on erosion, an erosion prediction method based on the Direct Simulation Monte Carlo (DSMC) method for calculation of particle collision and computational fluid dynamics was proposed. Herein, the Eulerian-Lagrangian method was adopted, the gas was taken as the continuous phase, the Navier-Stokes equations were solved, and the particle translation motion was solved by the Discrete Phase Model (DPM). For calculation of particle collision motion, the DSMC method was used to replace the real particles with a small number of sampled particles, and the collision conditions were judged by the corrected Nanbu method. Additionally, the effect of particle collision on elbow erosion rate and particle distribution in gas-solid two-phase flow was studied. The results show that the model error can be significantly reduced by calculating the particle collision with DSMC method, and the average percentage error of Oka model is reduced from 39.2% to 27.4%. For calculation of particle collision, the non-particle area on the inner arch side of the elbow becomes smaller, and the maximum erosion position moves backward 5° along the outer arch axis. Meanwhile, the flanks of the "V-shaped" erosion trace expand outward. Calculating the particle collision with DSMC method could significantly reduce the model error, and due to the small deviation from the experimental results, the Oka model considering particle collision is the best model for erosion prediction.

The existence of back pressure at outlet has a direct impact on the separation performance of the separation separator. However, the influence of back pressure is not understood well due to the complicated interaction of the supersonic flow, condensation and shock waves. In this study, the condensation flow models of water vapor were established, the influence of back pressure on supersonic condensation properties of water vapor was investigated. The results show that when the back pressure exists, the position of the shock wave is more forward than that without condensation, and the strength of shock wave is weaker. The nucleation rate is generated around the position of x = 115 mm and increases sharply from 0 to 1025 m−3 s−1. The shock wave is generated at x = 145 mm and x = 122 mm when the outlet back pressure is 20 kPa and 30 kPa, respectively. The condensed droplets evaporate again with the effect of shock wave, and then the secondary condensation of droplets occurs owing to the cooling effect of nozzle. When the back pressure is higher than a certain value, the refrigeration environment in the nozzle is completely destroyed with the effect of shock wave, and the condensed droplets evaporate again.

In view of the characteristics of strong penetration and extremely sensitive to delamination of materials, ultrasonic wave has unique advantages in coating defect detection. In order to quickly and accurately detect the defects of the outer coating of submarine oil and gas pipelines, and make up for the weakness of the existing coating detection technologies for oil and gas pipeline, such as low reliability, vulnerable to external interference, inaccurate positioning, etc., a pipeline coating defect detection method using ultrasonic pulse echo was proposed. Through ANSYS modeling and simulation calculation, the attenuation characteristics of reflected echo between intact coating interface and defective coating interface were compared, and obvious differences can be seen in the amplitude of echo after multiple reflections. The fifth echo signal was selected as the basis for determining the coating defects, and the reliability of simulation results was verified by designed test. This study shows that the method has high sensitivity to accurately detect coating defects. The operation is simple and reliable, not affected by the submarine complex environment, and meets the needs of continuous detection, so it can guarantee the safe and efficient operation of submarine oil and gas pipelines.

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.

Laval nozzle is the critical part of supersonic separator to provide refrigeration environment. Due to the back pressure at the outlet of supersonic separator in dehydration process, the condensation characteristics of water vapor and the refrigeration performances of the nozzles are affected by the shock wave. Herein, mathematical models for the supersonic condensation and flow of the methane-water two-phase flow model were established, which were verified by the experimental data. The effects of different divergent angles on the refrigeration and condensation behavior in the Laval nozzle were studied considering shock wave. The results show that the refrigeration performance of the nozzle will be worsen under the presence of shock waves. With the divergent angle of the nozzle increased from 2° to 8°, the lowest temperature was decreased from 304.4 K to 291.8 K, the liquid mass fraction at the nozzle outlet was decreased from 0.84% to 0.133%, the maximum droplet radius that can be obtained was reduced from 2.54 × 10−7 m to 1.69 × 10−7 m due to the forward movements of the shock waves. The divergent angle of the nozzle is recommended to be designed to 4°–6° in consideration of the refrigeration performance.

Rapid corrosion of steel bars in marine and complex saline environments has become a serious concern, and corrosion inhibitor for steel bar has proved to be one of the main protective measures to prevent the corrosion. In this paper, a new organic composite anti-corrosion agent (HTCI) was synthesised by hydrazine hydrate and tartaric acid for the preventing reinforced concrete from corrosion in marine engineering. The inhibition behaviors of HTCI for Q235 steel in saturated Ca(OH)2 solution with 3.0 wt.% NaCl were studied by weight loss, electrochemical measurement and surface analysis. All these techniques revealed that inhibition efficiency increased with increasing HTCI concentration and the inhibitor showed 84.37% inhibition efficiency at a concentration of 500 mg·L-1. Potentiodynamic polarization studies indicated the HTCI with mixed-type inhibitor properties. Scan analysis demonstrated that the depth of the pitting crater decreased with increasing HTCI concentration. Kinetically and thermodynamically simulated that the adsorption of HTCI on mild steel obeys Langmuir adsorption isotherm, and the mechanisms of this corrosion inhibitor were based on physical and chemical adsorption. [ABSTRACT FROM AUTHOR]