To investigate the leakage characteristics of pure hydrogen and hydrogen-blended natural gas in medium- and low-pressure buried pipelines, this study establishes a three-dimensional leakage model based on Computational Fluid Dynamics (CFD). The leakage characteristics in terms of pressure, velocity, and concentration distribution are obtained, and the effects of operational parameters, ground hardening degree, and leakage parameters on hydrogen diffusion characteristics are analyzed. The results show that the first dangerous time (FDT) for hydrogen leakage is substantially shorter than for natural gas, emphasizing the need for timely leak detection and response. Increasing the hydrogen blending ratio accelerates the diffusion process and decreases the FDT, posing greater risks for pipeline safety. The influence of soil hardening on gas diffusion is also examined, revealing that harder soils can restrict gas dispersion, thereby increasing localized concentrations. Additionally, the relationship between gas leakage time and distance is determined, aiding in the optimal placement of gas sensors and prediction of leakage timing. To ensure the safe operation of hydrogen-blended natural gas pipelines, practical recommendations include optimizing pipeline operating conditions, improving leak detection systems, increasing pipeline burial depth, and selecting materials with higher resistance to hydrogen embrittlement. These measures can mitigate risks associated with hydrogen leakage and enhance the overall safety of the pipeline infrastructure.

The formation of gas hydrates due to temperature and pressure changes during gas storage in the wellbore poses significant danger, necessitating the prediction of temperature and pressure distribution as well as of hydrate formation locations. We establish a temperature model that couples total thermal resistance and temperature in the wellbore-stratum composite medium system. Utilizing the two-phase pressure model alongside the temperature model, we conduct coupling calculations of temperature and pressure. Based on both temperature and pressure distribution within the wellbore and hydrate formation curve, we predict hydrate formation regions during production and analyze factors influencing temperature and pressure distribution. Results indicate that gas production rate and specific gravity of natural gas are major influencers on wellbore temperature and pressure distribution, while production time has minimal impact.

Nanoporous membranes offer significant advantages in direct contact membrane distillation applications due to their high flux and strong resistance to wetting. This study employs molecular dynamics simulations to explore the performance of membrane distillation in a single nanopore, mainly focusing on wetting behavior, liquid entry pressure, and membrane flux variations across different concentrations and types of salt solutions. The findings indicate that increasing the NaCl concentration enhances the wetting of membrane pores, thereby decreasing the entry pressure of the solution. However, at the same salt concentration, the differences in wetting and liquid entry pressure among various salts, including CaCl₂, KCl, NaCl, and LiCl, are minimal. The presence of hydrated ions significantly reduces membrane flux. As the concentration of NaCl solutions increases, the number of hydrated ions rises, thereby lowering the membrane flux of the salt solution. Furthermore, the type of salt has a pronounced effect on the structure of hydrated ions. Solutions with Ca²⁺ and Li⁺ exhibit the smallest first-layer radius of hydrated ions. Under the same salt concentration, KCl solutions demonstrate the highest membrane distillation flux, while CaCl₂ solutions show the lowest flux.

Hydrogen, as one of the most promising renewable clean energy sources, holds significant strategic importance and vast application potential. However, as a high-energy combustible gas, hydrogen poses risks of fire and explosion in the event of a leakage. Hydrogen production plants typically feature large spatial volumes and complex obstacles, which can significantly influence the diffusion pathways and localized accumulation of hydrogen during a short-term, high-volume release, further increasing the risk of accidents. Implementing effective hydrogen leakage monitoring measures can mitigate these risks, ensuring the safety of personnel and the environment to the greatest extent possible. Therefore, this paper uses CFD methods to simulate the hydrogen leakage process in a hydrogen production plant. The study examines the molar fraction distribution characteristics of hydrogen in the presence of obstacles by varying the ventilation speed of the plant and the directions of leakage. The main conclusions are as follows: enhancing ventilation can effectively prevent the rapid increase in hydrogen concentration, with higher ventilation speeds yielding better suppression. After a hydrogen leak in a confined space, hydrogen tends to diffuse along the walls and accumulate in corner areas, indicating that hydrogen monitoring equipment should be placed in corner locations.

Flashing flows of initially sub-cooled water in a converging–diverging nozzle is investigated numerically in the framework of the two-fluid model (TFM). The thermal non-equilibrium effect of phase change is considered by an interfacial heat transfer model, while the pressure jump across the interface is ignored. The bubble size distribution induced by nucleation, bubble growth/shrinkage, coalescence, and breakup is described based on the interfacial area transport equation (IATE) and constant bubble number density model (CBND), respectively. The results are compared with the experimental data. Satisfactory prediction of the axial pressure distribution along the nozzle as well as the flashing inception, is achieved by the TFM-IATE coupling method. It was also found that the vapor production in the diverging section was overpredicted, and the radial gas volume fraction distribution deviated from the experiment. The radial diameter profiles exhibit opposite patterns at the nozzle throat and near the outlet, and similar trends can be observed for the superheated degree. A poly-disperse method is suggested to be introduced to describe the evolution of interfacial area concentration.